Aviation Weather
University of Central Missouri Fall 2024 / Jupp / Aviation Weather Handbook FAA
Websites: Ventusky, Windy, Preduty briefing on weather.gov, awc, asrs on nasa.gov
Quizzes
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Quiz Chapter 8-9
Atmospheric pressure is the force per unit area exerted by the weight of the atmosphere
The aneroid barometer is the type most commonly used by meteorologists and the aviation community
Like most substances, air expands as it becomes warmer and contracts as it cools
Sea level pressure is typically displayed on surface weather charts
The density of an air parcel varies inversely with its volume
The density of an air parcel can be changed by changing its mass pressure, or temperature. Boyle’s Law says that the density of an ideal gas (rho) is given by: rho=MP/RT Where M is the molar mass, P is the pressure, R is the universal gas constant, and T is the absolute temperature
Density is inversely related to temperature
Density of an air parcel is inversely related to its quantity of water vapor
True altitude is the actual vertical distance above MSL
The altimeter setting is the value to which the scale of the pressure altimeter is set so the altimeter indicates true altitude at field elevation
If flying in cold weather over mountainous areas, however, pilot needs to take this difference between indicated and true altitude into account. The pilot needs to know that the true altitude assures clearance of terrain, and compute a correction to indicated altitude
Density altitude is the pressure altitude corrected for temperature deviations from the standard atmosphere
Density altitude is an index to aircraft performance. Higher density altitude decreases aircraft performance. Lower density altitude increases aircraft performance.
Hadley cell- Low-latitude air movement toward the Equator that, with heating, rises vertically with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and subtropical climates
Ferrel cell- A mid-latitude mean atmospheric circulation cell for weather, named by William Ferrel in the 19th century. In this cell, the air flows poleward and eastward near the surface, and equatorward and westward at higher levels
Polar cell- Air rises, diverges, and travels toward the poles. Once over the poles, the air sinks, forming polar highs. At the surface, air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies)
Jet streams follow the boundaries between hot and cold air. Since these hot and cold air boundaries are most pronounced in winter, jet streams are the strongest for both the Northern and Southern Hemisphere winters
Jet streams vary in height from around flight level (FL) 200 to FL450 and can reach speeds of more than 275 miles per hour (mph) 239 knots (kts)
Quiz Chapter 10
Wind is named according to the direction from which it is blowing.
Whenever a pressure difference develops over an area, the Pressure Gradient Force (PGF) makes the wind blow in an attempt to equalize pressure differences.
PGF is directed from higher height/pressure to lower height/pressure and is perpendicular to contours/isobars.
Coriolis force is an apparent force that affects all moving objects. The force deflects air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Friction between the wind and the terrain surface slows the wind.
When a PGF is first established, wind begins to blow from higher to lower heights directly across the height contours. However, the instant air begins moving,Coriolis force deflects it to the right. Soon the wind is deflected a full 90° and is parallel to the height contours. At this time, Coriolis force exactly balances PGF. With the forces in balance, wind will remain parallel to height contours. This is called the geostrophic wind.
In the Northern Hemisphere, the surface wind spirals clockwise and outward from high pressure, and counterclockwise and inward into low pressure.
A sea breeze is a coastal local wind that blows from sea to land and is caused by temperature differences when the sea surface is colder than the adjacent land.
A land breeze is a coastal breeze blowing from land to sea caused by the temperature difference when the sea surface is warmer than the adjacent land.
A valley breeze is a wind that ascends a mountain valley during the day. Air in contact with the sloping terrain becomes warmer (less dense) than air above the valley.
A mountain breeze is the nightly downslope winds commonly encountered in mountain valleys. Air in contact with the sloping terrain cools faster than air above the valley.
A gust is a fluctuation of wind speed with variations of 10 knots (kt) or more between peaks and lulls.
Quiz Chapter 11
Air masses are classified according to the temperature and moisture properties of their source regions.
Temperature Properties • Arctic (A)—An extremely deep, cold air mass that develops mostly in winter over arctic surfaces of ice and snow.
Temperature Properties • Polar (P)—A relatively shallow, cool to cold air mass that develops over high latitudes.
Temperature Properties • Tropical (T)—A warm to hot air mass that develops over low latitudes.
Moisture Properties • Continental (c)—A dry air mass that develops over land.
Moisture Properties • Maritime (m)—A moist air mass that develops over water
Continental Arctic (cA) - Cold, Dry. Continental Polar (cP) - Cold, dry. Continental Tropical (cT) - Hot, dry. Maritime Polar (mP) - Cool, moist. Maritime Tropical (mT) - Warm, moist.
Air Mass Modification - As these air masses move around the Earth, they can begin to acquire different attributes.
Lake effect is the effect of any lake in modifying the weather near its shore and for some distance downwind.
A front is a boundary or transition zone between two air masses. Fronts are classified by which type of air mass (cold or warm) is replacing the other.
A warm front occurs when a warm mass of air advances and replaces a body of colder air. Warm fronts move slowly, typically 10 to 25 mph. The slope of the advancing front slides over the top of the cooler air and gradually pushes it out of the area.
A cold front occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air. It is so dense, it stays close to the ground and acts like a snowplow, sliding under the warmer air and forcing the less dense air aloft. Cold fronts have a steep slope, and the warm air is forced upward abruptly.
A continuous line of thunderstorms, or squall line, may form along or ahead of the front. Squall lines present a serious hazard to pilots as squall-type thunderstorms are intense and move quickly.
When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. This front is called a stationary front. Stationary frontal slope can vary, but clouds and precipitation would still form in the warm rising air along the front.
Cold fronts typically move faster than warm fronts, so in time they catch up to warm fronts. As the two fronts merge, an occluded front forms. At the occluded front, the cold air undercuts the retreating cooler air mass associated with the warm front, further lifting the already rising warm air.
A wave cyclone is a low-pressure circulation that forms and moves along a front. The circulation about the cyclone center tends to produce a wavelike kink along the front.
A dryline is a low-level boundary hundreds of miles long separating moist and dry air masses.
Quiz Chapter 12-15
a bubble or parcel of air ascends (rises), it moves into an area of lower pressure (pressure decreases with height). As this occurs, the parcel expands. This requires energy (or work), which takes heat away from the parcel, so the air cools as it rises.
The lapse rate of a rising, unsaturated parcel (air with relative humidity less than 100 percent) is approximately 3 °C per 1,000 ft (9.8 °C per km). This is called the dry adiabatic lapse rate.
The Lifted Condensation Level (LCL) is the level at which a parcel of moist air lifted dry adiabatically becomes saturated. At this altitude, the temperature-dewpoint spread is zero and relative humidity is 100 percent. Further lifting of the saturated parcel results in condensation, cloud formation, and latent heat release.
Orographic Effects: Winds blowing across mountains and valleys cause the moving air to alternately ascend and descend. If relief is sufficiently great, the resulting expansional cooling and compressional warming of air affects the development and dissipation of clouds and precipitation.
Frontal lift occurs when the cold, denser air wedges under the warm, less dense air, plowing it upward, and/or the warmer air rides up and over the colder air in a process called overrunning. Clouds and precipitation will form given sufficient lift and moisture content of the warm air.
Cirri-form: High-level clouds that form above 20,000 ft (6,000 m) and are usually composed of ice crystals. High-level clouds are typically thin and white in appearance, but can create an array of colors when the Sun is low on the horizon. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.
Nimbo-form: Nimbus comes from the Latin word meaning “rain.” These clouds typically form between 7,000 and 15,000 ft (2,100 to 4,600 m) and bring steady precipitation. As the clouds thicken and precipitation begins to fall, the bases of the clouds tend to lower toward the ground.
Cumuli-form: Clouds that look like white, fluffy cotton balls or heaps and show the vertical motion or thermal uplift of air taking place in the atmosphere. The level at which condensation and cloud formation begins is indicated by a flat cloud base, and its height will depend upon the humidity of the rising air. The more humid the air, the lower the cloud base. The tops of these clouds can reach over 60,000 ft.
Strati-form: Stratus is Latin for “layer” or “blanket.” The clouds consist of a featureless low layer that can cover the entire sky like a blanket, bringing generally gray and dull weather. The cloud bases are usually only a few hundred feet above the ground. Over hills and mountains, they can reach ground level when they may be called fog. Also, as fog lifts off the ground due to daytime heating, the fog forms a layer of low stratus clouds.
Atmospheric stability is the property of the ambient air that either enhances or suppresses vertical motion of air parcels and determines which type of clouds and precipitation a pilot will encounter.
Absolute stability is the state of a column of air in the atmosphere when its lapse rate of temperature is less than the moist adiabatic lapse rate.
Neutral stability is the state of a column of air in the atmosphere in which an ascending (or descending) air parcel always has the same temperature (density) as the surrounding environmental air.
Conditional instability is the state of a column of unsaturated air in the atmosphere when its lapse rate of temperature is less than the dry adiabatic lapse rate, but greater than the moist adiabatic lapse rate. An air parcel lifted upward would be initially stable, but at some point above its Lifting Condensation Level (LCL) it would become unstable.
Daytime heating of the surface increases temperature lapse rates and decreases stability. Conversely, nighttime cooling of the surface decreases temperature lapse rates and increases stability.
The Lifted Index (LI) is the temperature difference between an air parcel (usually at the surface) lifted adiabatically and the temperature of the environment at a given pressure (usually 500 mb) in the atmosphere. A positive value indicates a stable column of air (at the respective pressure), a negative value indicates an unstable column of air, and a value of zero indicates a neutrally stable column of air.
Precipitation formation requires three ingredients: water vapor, sufficient lift to condense the water vapor into clouds, and a growth process that allows cloud droplets to grow large and heavy enough to fall as precipitation.
Two growth processes exist that allow cloud droplets (or ice crystals) to grow large enough to reach the ground as precipitation before they evaporate (or sublimate). One process is called the collision-coalescence, or warm rain process. The other process is called the ice crystal process.
Snow occurs when the temperature remains below freezing throughout the entire depth of the atmosphere.
Ice pellets (sleet) occur when there is a shallow layer aloft with above-freezing temperatures and with a deep layer of below-freezing air based at the surface.
Freezing rain occurs when there is a deep layer aloft with above-freezing temperatures and with a shallow layer of below-freezing air at the surface.
Hail forms when supercooled water droplets above the freezing level begin to freeze. Once a droplet has frozen, other droplets latch on and freeze to it, so the hailstone grows—sometimes into a huge iceball.
The most effective tool to detect precipitation is radar. Radar, which is an acronym that stands for “radio detection and ranging,” has been utilized to detect precipitation since the 1940s.
The radar antenna alternately emits and receives radio waves into the atmosphere. Pulses of energy from the radio waves may strike a target. If they do, part of that energy will return to the antenna.
Range attenuation is automatically compensated for by the WSR-88D. However, most airborne radars only compensate for range attenuation out to a distance of 50 to 75 NM. Targets beyond these ranges will appear less intense than they actually are.
Under normal conditions, the atmosphere’s density gradually decreases with increasing height. As a result, the upper portion of a radar beam travels faster than the lower portion of the beam. This causes the beam to bend downward.
Subrefraction may cause the radar beam to overshoot objects that would normally be detected. For example, distant thunderstorms may not be detected with subrefraction. Subrefraction may also cause radar to underestimate the true strength of a thunderstorm.
Sometimes the density of the atmosphere decreases with height at a less-than-normal rate (actual density is greater than normal) or even increases with height. When this occurs, the radar beam will bend more than normal toward the Earth’s surface. This phenomenon is called superrefraction.
If the atmospheric condition that causes superrefraction bends the beam equal to, or greater than, the Earth’s curvature, then a condition called ducting (or trapping) occurs. When ducting occurs, the radar beam will hit the surface of the Earth, causing some of the beam’s energy to backscatter.
Ground clutter is radar echoes’ returns from trees, buildings, or other objects on the ground. It appears as a roughly circular region of high reflectivity at ranges close to the radar.
Convective precipitation is distinguished by the following radar characteristics:
• Echoes tend to form as lines or cells;
• Reflectivity gradients are strong;
• Precipitation intensities generally vary from moderate to extreme;
• Occasionally, precipitation intensities can be light; and
• Echo patterns change rapidly when animating the image.
Stratiform precipitation has the following radar characteristics:
• Widespread in aerial coverage;
• Weak reflectivity gradients;
• Precipitation intensities are generally light or moderate (39 dBZ or less);
• Occasionally, precipitation intensities can be stronger; and
• Echo patterns change slowly when animating the image.
Bright band is a distinct feature observed by radar that denotes the freezing (melting) level. These particles reflect significantly more energy (appearing to the radar as large raindrops) than the portions of the cloud above and below the freezing layer.
Quiz Chapter 16-17
Strong winds flow over or around mountains or ridges. If the surrounding atmosphere is unstable, the vertical displacement of the air will (if sufficient moisture is present) lead to thunderstorm formation or at least the development of deep convective clouds. However, if the wind is sufficiently strong and the surrounding atmosphere is stable, a wave will develop.
In order for gravity waves to develop, the atmosphere must possess at least some degree of static stability.
Kelvin-Helmholtz (K-H) instability induced by the wind shear associated with strong winds aloft is likely the chief source of high-level turbulence away from mountain ranges (Clear Air Turbulence (CAT).
Mountain Waves are air that is moving nearly perpendicular to the barrier is deflected upward and accelerated as it passes over the crests and down the lee slopes of the terrain.
Trapped Lee Waves are a type of mountain wave that propagates a train of Altocumulus Standing Lenticular (lens- or airfoil-shaped clouds) extending far downwind of the mountain (although trapped lee waves frequently occur without clouds).
When mountain waves are present, it is quite common for a rotor zone to develop near or below ridge level on the downwind side of the mountain, under a wave crest and associated lenticular cloud (if sufficient moisture is present). This is an area of potentially severe-to-extreme wind shear and turbulence.
Occasionally, an extremely strong low-level temperature inversion can occur in mountainous areas, with the inversion top below ridge level (perhaps 900 to 1,000 ft AGL) and a pool of very cold air at the surface. If this phenomenon occurs with strong wind flow above the inversion layer, there will be a concentrated shear zone near the inversion, which can lead to both significant turbulence encounters and abrupt airspeed changes for aircraft that penetrate the inversion on climbout or during descent.
There are at least two primary causes of boras: 1) cold fronts aligned parallel to the mountain range and moving perpendicular to it, with the cold air eventually spilling over; and 2) cold outflow, from thunderstorms over or near a mountain range, that builds up to sufficient depth to spill over and down the opposite slope.
The trade winds converge in the vicinity of the equator where air rises. This convergence zone is referred to as the Intertropical Convergence Zone (ITCZ).
The subtropical highs shift southward during the Northern Hemisphere winter and northward during summer.
Continental Weather Along the west coasts of continents under a subtropical high, the air is stable. The inversion is strongest and lowest where the east side of the subtropical high-pressure area overlies the west side of a continent. The extreme southwestern United States, for example, is dominated in summer by a subtropical high
On eastern continental coasts the inversion is weakest and highest where the west side of the subtropical high-pressure area overlies the eastern coast of a continent. Convection can penetrate the inversion, and showers and thunderstorms often develop.
Trade winds blowing out of the subtropical highs over ocean areas are predominantly northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.
Many islands in the trade wind belt have lush vegetation and even rain forests on the windward side, while the leeward is semiarid.
Convection in the Intertropical Convergence Zone (ITCZ) carries huge quantities of moisture to great heights. Showers and thunderstorms frequent the ITCZ, and tops to 40,000 ft or higher are common.
Over the large land mass of Asia, an intense high during the winter and a well-developed low during the summer. The cold, high pressures in winter cause wind to blow from the deep interior outward and offshore. In summer, wind direction reverses, and warm moist air is carried far inland into the low-pressure area. This large-scale seasonal wind shift is the monsoon. The most notable monsoon is that of southern and southeastern Asia.
A shear line, results when a semipermanent high splits into two cells, inducing a trough. These shear lines are zones of convergence creating forced upward motion. Consequently, considerable thunderstorm and rain shower activity occurs along a shear line.
Tropical Upper Tropospheric Trough (TUTT) generally at or above 10,000 ft, move through the Tropics, especially along the poleward fringes. These are known as TUTTs. As a TUTT moves to the southeast or east, it spreads middle and high cloudiness over extensive areas to the east of the trough line.
On occasion, a line of convection similar to a squall line moves westward off the continent at tropical latitudes into the oceanic trade winds. In the North Atlantic, this is known as the West African Disturbance Line (WADL). A WADL can move faster than easterly waves at 20 to 40 mph. Some WADLs eventually develop into tropical storms or hurricanes.
“Tropical cyclone” is a general term for any low that originates over tropical oceans. Tropical cyclones are classified according to their intensity based on the average wind speeds.
Over the north Atlantic and northeast Pacific Oceans, tropical cyclone classifications are:
Tropical Depression —sustained winds up to 34 kt (64 km/h).
Tropical Storm—sustained winds of 35 to 64 kt (65 to 119 km/h).
Hurricane—sustained winds of at least 65 kt (120 km/h) or more.
Tropical cyclones are unlikely within 5° of the Equator because the coriolis force is so small near the Equator that it will not turn the winds enough for them to flow around a low-pressure area.
Most tropical cyclones that form eyes do so within 48 hours of the cyclone reaching tropical storm strength. In the eye, skies are free of turbulent cloudiness, and wind is comparatively light.
Level 3
Most newer mobile homes will sustain severe damage with potential for complete roof failure and wall collapse. Poorly constructed frame homes can be destroyed by the removal of the roof and exterior walls. Unprotected windows will be broken by flying debris. Well-built frame homes can experience major damage involving the removal of roof decking and gable ends.
Level 2
Poorly constructed frame homes have a high chance of having their roof structures removed, especially if they are not anchored properly. Unprotected windows will have a high probability of being broken by flying debris. Well-constructed frame homes could sustain major roof and siding damage. Failure of aluminum, screened-in, swimming pool enclosures will be common
Level 5
.A high percentage of frame homes will be destroyed, with total roof failure and wall collapse. Extensive damage to roof covers, windows, and doors will occur.
Level 4
Poorly constructed frame homes can sustain complete collapse of all walls as well as the loss of the roof structure. Well-built homes also can sustain severe damage with loss of most of the roof structure and/or some exterior walls.
Level 1
Newer mobile homes that are anchored properly can sustain damage involving the removal of shingle or metal roof coverings, and loss of vinyl siding, as well as damage to carports, sunrooms, or lanais. Some poorly constructed frame homes can experience major damage, involving loss of the roof covering and damage to gable ends, as well as the removal of porch coverings and awnings.
Quiz Chapter 18-21
Fog forms when the temperature and dewpoint of the air become identical (or nearly so). This may occur through cooling of the air to its dewpoint (producing radiation fog, advection fog, or upslope fog), or by adding moisture and thereby elevating the dewpoint (producing frontal fog or steam fog).
Fog types are named according to their formation mechanism.
Radiation fog is a common type of fog, produced over a land area when radiational cooling reduces the air temperature to or below its dewpoint.
Advection fog forms when moist air moves over a colder surface and the subsequent cooling of that air to below its dewpoint.
Upslope fog forms as a result of moist, stable air being adiabatically cooled to or below its dewpoint as it moves up sloping terrain
When warm, moist air is lifted over a front, clouds and precipitation may form. If the cold air below is near its dewpoint, evaporation (or sublimation) from the precipitation may saturate the cold air and form fog
Steam Fog When very cold air moves across relatively warm water, enough moisture may evaporate from the water surface to produce saturation.
Freezing fog occurs when the temperature falls to 32 °F (0 °C) or below. Tiny, supercooled liquid water droplets in fog can freeze instantly on exposed surfaces when surface temperatures are at or below freezing.
Mist is a visible aggregate of minute water droplets or ice crystals suspended in the atmosphere that reduces visibility to less than 7 sm (11 km), but greater than, or equal to, 5/8 sm (1 km).
Haze is a suspension in the air of extremely small particles invisible to the naked eye and sufficiently numerous to give the air an opalescent appearance. It reduces visibility by scattering the shorter wavelengths of light
Smoke is a suspension in the air of small particles produced by combustion due to fires, industrial burning, or other sources.
Blowing snow is snow lifted from the surface of the Earth by the wind to a height of 6ft (2 m) or more above the ground, and blown about in such quantities that the reported horizontal visibility is reduced to less than 7 sm
A dust storm is a severe weather condition characterized by strong winds and dust-filled air over an extensive area. Dust storms originate over regions when fine-grained soils, rich in clay and silt, are exposed to strong winds and lofted airborne.
A sandstorm is particles of sand carried aloft by a strong wind. The sand particles are mostly confined to the lowest 10 ft (3.5 m), and rarely rise more than 50 ft (15 m) above the ground. Sandstorms are similar to dust storms, but occur on a localized scale.
A haboob is a dust storm or sandstorm that forms as cold downdrafts from a thunderstorm turbulently lift dust and sand into the air. While haboobs are often short-lived, they can be quite intense. The dust wall may extend horizontally for more than 60 mi (100 km) and rise vertically to the base of the thunderstorm
Volcanic ash is made up of fine particles of rock powder that originate from a volcano and that may remain suspended in the atmosphere for long periods. Severe volcanic eruptions that send ash into the upper atmosphere occur somewhere around the world several times per year.
Stratus is the most frequent cloud associated with low ceilings. Stratus clouds, like fog, are composed of extremely small water droplets or ice crystals suspended in air.
Convective turbulence is turbulent vertical motions that result from convective currents and the subsequent rising and sinking of air. For every rising current, there is a compensating downward current.
When the air is too dry for cumuliform clouds to form, convective currents can still be active. This is called dry convection, or thermals. A pilot has little or no indication of their presence until encountering the turbulence.
Turbulence is present in all thunderstorms, and severe or extreme turbulence is common. A severe thunderstorm can destroy an aircraft. Gust loads can be severe enough to stall an aircraft at maneuvering speed or to cause structural damage at cruising speed. The strongest turbulence within the cloud occurs between updrafts and downdrafts.
Mechanical turbulence is turbulence caused by obstructions to the wind flow, such as trees, buildings, mountains, and so on
Strong wind shears often occur across temperature inversion layers, which can generate turbulence
One of the principal areas where Clear Air Turbulence (CAT) is found is in the vicinity of the jet streams.
Nonconvective LLWS is defined as a wind shear of 10 kt or more per 100 ft in a layer more than 200 ft thick that occurs within 2,000ft of the surface.
Pure water suspended in the air does not freeze until it reaches a temperature of -40 °C. This occurs because surface tension of the droplets inhibits freezing.
Rime ice is rough, milky, and opaque ice formed by the instantaneous freezing of small, supercooled water droplets after they strike the aircraft. It is the most frequently reported icing type.
Clear ice (or glaze ice) is a glossy, clear, or translucent ice formed by the relatively slow freezing of large, supercooled water droplets. Clear icing conditions exist more often in an environment with warmer temperatures, higher liquid water contents, and larger droplets.
Supercooled Large Drops (SLD) A type of clear icing that is especially dangerous to flight operations is ice formed from SLDs. These are water droplets in a subfreezing environment with diameters larger than 40 microns, such as freezing drizzle (40 to 200 microns) and freezing rain (>200 microns).
Mixed ice is a mixture of clear ice and rime ice
Supercooled Liquid Water Content (SLWC) is important in determining how much water is available for icing. The highest quantities can be found in cumuliform clouds, with the lowest quantities found in stratiform clouds. However, in most icing cases, SLWC is low.
The only physical cold limit to icing is at -40 °C because liquid droplets freeze without nuclei present.
Most icing reports occur in the vicinity of fronts.
Icing with mountains can be especially hazardous because a pilot may be unable to descend to above-freezing temperatures due to terrain elevation
Structural icing degrades an aircraft’s performance. It destroys the smooth flow of air, increasing drag while decreasing the ability of the airfoil to create lift. The actual weight of ice on an airplane is insignificant when compared to the airflow disruption it causes.
Any point north of the Arctic Circle has autumn and winter days when the Sun stays below the horizon all day and has spring and summer days with 24 hours of sunshine when the Sun stays above the horizon.
Quiz Chapter 22-23
A thunderstorm is a local storm, invariably produced by a cumulonimbus (CB) cloud, and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes hail.
Thunderstorm cell formation needs three ingredients: sufficient water vapor, unstable air, and a lifting mechanism.
A thunderstorm cell is the convective cell of a cumulonimbus cloud having lightning and thunder. It undergoes three distinct stages during its life cycle: towering cumulus, mature, and dissipating.
The distinguishing feature of the towering cumulus stage is a strong convective updraft.
The cell transitions to the mature stage when precipitation reaches the surface.
The dissipating stage is marked by a strong downdraft embedded within the area of precipitation. Subsiding air replaces the updraft throughout the cloud, effectively cutting off the supply of moisture provided by the updraft.
There are three principal thunderstorm types: single-cell, multicell (cluster and line), and supercell.
With an organized multicell cluster, as the first cell matures, it is carried downwind, and a new cell forms upwind to take its place. A multicell cluster may have a lifetime of several hours (or more). New cells will continue to form as long as the three necessary ingredients exist.
A supercell thunderstorm is an often dangerous, long-lived convective storm that consists primarily of a single, quasi-steady rotating updraft that persists for an extended period of time. It has a very organized internal structure that enables it to produce especially dangerous weather for pilots who encounter them. Updraft speeds may reach 9,000 fpm (100 kt).
Storm motion equals the combined effects of both advection and propagation.
Derecho is a widespread, long-lived, straight-line windstorm that is associated with a fast-moving band of severe thunderstorms.
While not every thunderstorm contains all hazards, it is not possible to visually determine which hazards a thunderstorm contains. Hazards include: low ceiling and visibility, lightning, adverse winds, downbursts, turbulence, icing, hail, rapid altimeter changes, static electricity, tornadoes, and engine water ingestion.
Every thunderstorm produces lightning and thunder by definition. Lightning is a visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between a cloud and air, between a cloud and the ground, or between the ground and a cloud.
Downbursts can create hazardous conditions for pilots and have been responsible for many LLWS accidents. Smaller, shorter-lived downbursts are called microbursts.
It is vital for pilots to recognize that some microbursts cannot be successfully escaped with any known techniques. Some wind shears that are within the performance capability of the aircraft have caused accidents.
Vertical winds exist in every microburst and increase in intensity with altitude. Such winds usually reach peak intensity at heights greater than 500 ft above the ground. Downdrafts with speeds greater than 3,000 fpm can exist in the center of a strong microburst.
Pressure usually falls rapidly with the approach of a thunderstorm. Pressure then usually rises sharply with the onset of the first gust and arrival of the cold downdraft and heavy rain, falling back to normal as the thunderstorm passes.
The corona discharge is weakly luminous and may be seen at night. Although it has a rather eerie appearance, it is harmless. It was named “St. Elmo’s Fire” by Mediterranean sailors, who saw the brushy discharge at the top of ship masts.
The most violent thunderstorms draw air into their cloud bases with great force. If the incoming air has any initial rotating motion, it often forms an extremely concentrated vortex from the surface well into the cloud.
Enhanced Fujita Scale
EF-0 (65-85mph),
EF-1 (86-110mph),
EF-2 (111-135mph),
EF-3 (135-165mph),
EF-4 (166-200mph),
EF-5 (>200mph)
Over 80 percent of all tornadoes in the United States are produced by supercell thunderstorms.
It is important to note that while hail always gives a radar echo, it may fall several miles from the nearest visible cloud, and hazardous turbulence may extend to as much as 20 mi from the echo edge.
Avoid by at least 20 miles any thunderstorm identified as severe or giving an intense, heavy, or extreme radar echo.
Do not turn back once in the thunderstorm. A straight course through the storm most likely will get the aircraft out of the hazards most quickly. In addition, turning maneuvers increase stress on the aircraft.
The Sun is the dominant source of the conditions commonly described as space weather. Emissions from the Sun are both continuous (e.g., solar luminescence and solar wind) and eruptive (e.g., coronal mass ejections (CME) and flares). These solar eruptions may cause radio blackouts, magnetic storms, ionospheric storms, and radiation storms at Earth.
The Sun is a variable star. That means the balance between the continuous emissions and the eruptive emissions changes with time. One metric that is commonly used to track this variability is the occurrence of sunspots.
Earth’s magnetic field extends outward in all directions. This forms a cocoon for the planet, protecting it from the flow of the solar wind. The cocoon is called the magnetosphere.
The most visible manifestation of the energy being absorbed from the solar wind into the magnetosphere is the aurora, both in the Northern and Southern Hemispheres. The aurora occurs when accelerated electrons from the Sun follow the magnetic field of Earth down to the polar regions, where they collide with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere.
The symptoms of an ionospheric storm include enhanced currents, turbulence and wave activity, and a nonhomogeneous distribution of free electrons. This clustering of electrons, which leads to scintillation of signals passing through the cluster, is particularly problematic for the Global Navigation Satellite System (GNSS), which includes the United States’ GPS.
Solar radiation storms occurring under particular circumstances cause an increase in radiation dose to flight crews and passengers. As high polar latitudes and high altitudes have the least shielding from the particles, the threat is the greatest for higher altitude polar flights.
Quiz Chapter 24.1-35
Observations are weather data collected automatically by sensor(s), manually by trained weather observers, or by a combination of both, and are the basic information upon which forecasts and advisories are made in support of a wide range of weather-sensitive activities within the public and private sectors, including aviation.
Manual surface weather observations are made by a human weather observer who is certified by the FAA.
Automated observations are derived from instruments and algorithms without human input or oversight.
Augmented Observation are the addition of human observers to report weather elements that are beyond the capabilities of the automated system and/or are deemed operationally significant.
AWOS generates a METAR at 20-minute intervals and does not report SPECIs. AWOS also provides OMOs available by phone or radio.
METARs are sometimes referred to as “hourly” reports since they are routinely produced near the top of the hour.
A SPECI is an unscheduled report taken when any of the criteria given in Table 24-2 are observed during the period between hourly reports. SPECIs contain all data elements found in a METAR. All SPECIs are issued as soon as possible when relevant criteria are observed.
The station identifier, in ICAO format, is included in all reports to identify the station to which the coded report applies. The ICAO airport code is a four-letter alphanumeric code designating each airport around the world.
The coded time of observations is the actual time of the report, or when the criteria for a SPECI is met or noted. The date and time group always ends with a Z, indicating Zulu time (or Coordinated Universal Time (UTC)).
In the wind group, the wind direction is coded as the first three digits and is determined by averaging the recorded wind direction over a 2-minute period. Immediately following the wind direction is the wind speed coded in two or three digits. Wind speed is determined by averaging the speed over a 2-minute period and is coded in whole knots using the units, tens digits, and, when appropriate, the hundreds digit.
The visibility group is coded as the surface visibility in statute miles. A space is coded between whole numbers and fractions of reportable visibility values. The visibility group ends with SM to indicate that the visibility is in statute miles. For example, a visibility of 1½ sm is coded 1 1/2SM. U.S. automated stations use an M to indicate “less than.” For example, M1/4SM means a visibility of less than ¼ sm
The Runway Visual Range (RVR) is an instrument-derived value representing the horizontal distance a pilot may see down the runway. RVR is reported whenever the station has RVR equipment and prevailing visibility is 1 sm or less, and/or the RVR for the designated instrument runway is 6,000 ft or less
Obscuration Reporting (METAR Codes)
Weather phenomena occurring beyond the point of observation (between 5 and 10 sm) are coded as in the vicinity (VC).
Precipitation Types (METAR Codes)
The sky condition group is based on the amount of cloud cover (the first three letters) followed by the height of the base of the cloud cover (final three digits). The height of the layer is recorded in feet AGL.
The altimeter group always starts with an A and is followed by the four-digit group representing the pressure in tens, units, tenths, and hundredths of inches of mercury
Type of Automated Station AO1 or AO2 is coded in all METARs/SPECIs from automated stations. Automated stations without a precipitation discriminator are identified as AO1; automated stations with a precipitation discriminator are identified as AO2.
When lightning is detected by an automated system: • Within 5 NM of the Airport Location Point (ALP), it is reported as TS in the body of the report with no remark.
Beginning and Ending of Precipitation At designated stations, the beginning and ending times of precipitation are coded in the following format: the type of precipitation, followed by either a B for beginning or an E for ending, and the time of occurrence.
If the pressure is rising or falling at a rate of at least 0.06 in per hour and the pressure change totals 0.02 in or more at the time of the observation, a pressure change remark is reported. When the pressure is rising or falling rapidly at the time of observation, the remark pressure rising rapidly (PRESRR) or pressure falling rapidly (PRESFR) is included in the remarks.
A maintenance indicator ($) is coded when an automated system detects that maintenance is needed on the system.
Pilot Weather Reports (PIREP) Pilots can report any observation, good or bad, to assist other pilots with flight planning and preparation. If conditions were forecasted to occur but not encountered, a pilot can also report the observed condition.
Urgent (UUA) PIREPs contain information about:
• Tornadoes, funnel clouds, or waterspouts;
• Severe or extreme turbulence (including CAT);
• Severe icing;
• Hail;
• LLWS within 2,000 ft of the surface (LLWS PIREPs are classified as UUA if the pilot reports air speed fluctuations of 10 kt or more; or if air speed fluctuations are not reported but LLWS is reported, the PIREP is classified as UUA);
• Volcanic ash clouds; and/or
• Any other weather phenomena reported that are considered by the air traffic controller or Flight Service specialist receiving the report as being hazardous, or potentially hazardous, to flight operations
Pilot Weather Reports: Turbulence intensity, type, and altitude are reported after wind direction and speed. Duration (intermittent (INTMT), occasional (OCNL), or continuous (CONS)) is coded first (if reported by the pilot), followed by the intensity (light (LGT), moderate (MOD), severe (SEV), or extreme (EXTRM)). Range or variation of intensity is separated with a hyphen (e.g., MOD-SEV). If turbulence was forecast, but not encountered, negative (NEG) is entered
Pilot Weather Reports: Icing intensity, type, and altitude are reported after turbulence. Intensity is coded first using contractions TRACE, light (LGT), moderate (MOD), or severe (SEV). Reports of a range or variation of intensity is separated with a hyphen. If icing was forecast but not encountered, negative (NEG) is coded. Icing type is reported second. Reportable types are RIME, clear (CLR), or mixed (MX).
AIREPs are messages from an aircraft to a ground station
Midterm
Chapter 24.36-60, 25 Quiz
Modern commercial aircraft are equipped with meteorological sensors and associated sophisticated data acquisition and processing systems. These systems continuously record meteorological information on the aircraft and send these observations at selected intervals to ground stations via satellite or radio links where they are processed and disseminated.
WSR-88D radars are continuously generating radar observations. Each radar observation, called a volume scan, consists of 5 to 14 separate elevation “tilts,” and takes between 4 and 11 minutes to generate, depending on the radar’s mode of operation.
The WSR-88D radar network consists of 160 radars operated by the NWS, FAA, and DOD.
The WSR-88D is operated in Precipitation Mode when precipitation is present, although some nonprecipitation echoes can still be detected in this operating mode. The NWS uses Precipitation Mode to see higher into the atmosphere when precipitation is occurring to analyze the vertical structure of the storms. The faster rotation of the WSR-88D in Precipitation Mode allows images to update at a faster rate, approximately every 4 to 6 minutes.
WSR-88D radar reflectivity is correlated to intensity of precipitation. For example, in Precipitation Mode, when the decibel value reaches 15, light precipitation is present. The higher the indicated reflectivity value, the higher the rainfall rate
A radar mosaic consists of multiple single-site radar images combined to produce a radar image on a regional or national scale
Composite Reflectivity is the maximum echo intensity (reflectivity) detected within a column of the atmosphere above a location. During its tilt sequence, the radar scans through all of the elevation slices to determine the highest decibel value in the vertical column, then displays that value on the product
The Base Reflectivity product is a display of both the location and intensity of reflectivity data from the lowest elevation angle scan, or 0.5º above the horizon. Base Reflectivity is also known as “Lowest Tilt” and “Reflectivity at Lowest Altitude,” depending on the website or weather data service provider
The terminal Doppler weather radar (TDWR) is a Doppler weather radar system operated by the FAA, which is used primarily for the detection of hazardous wind shear conditions, precipitation, and winds aloft on and near major airports situated in climates with great exposure to thunderstorms
GeoColor imagery is a multispectral product composed of true color (using a simulated green component) during the daytime, and an IR product at night. During the day, the imagery looks approximately as it would appear when viewed with human eyes from space.
Visible imagery displays reflected sunlight from the Earth’s surface, clouds, and particulate matter in the atmosphere. Visible satellite images, which look like black and white photographs, are derived from the satellite signals.
IR images display temperatures of the Earth’s surface, clouds, and particulate matter.
Water vapor imagery displays the quantity of water vapor generally located in the middle and upper troposphere within the layer between 700 mb (approximately 10,000 ft MSL) and 200 mb (approximately FL390). The most useful information to be gained from the water vapor images is the locations and movements of weather systems, jet streams, and thunderstorms.
“POES” stands for the Polar Operational Environment Satellites. Polar satellites are not stationary. They track along various orbits around the poles
The radiosonde is a small, expendable instrument package (weighing 100 to 500 g), which consists of radio gear and sensing elements, that is suspended below a large balloon inflated with hydrogen or helium gas.
Weather balloons with radiosondes are launched twice a day worldwide from designated locations at around 1100 UTC and 2300 UTC. It takes approximately 90 minutes for the balloon to reach an altitude of 100,000 ft.
Visual Weather Observation System (VWOS), which is available on the FAA’s Aviation Weather Camera Network, is an advanced camera system that is comprised of a suite of weather sensors and 360-degree camera images that collectively observe and report several critical data fields, including winds, cloud height, visibility, present weather, temperature, dewpoint, and pressure.
Surface weather charts depict weather on a constant-altitude (usually sea level) surface, while upper air charts depict weather on constant-pressure surfaces.
Analysis is the drawing and interpretation of the patterns of various elements on a weather chart. Computers cannot interpret what they analyze. Thus, many meteorologists still perform a subjective analysis of weather charts when needed.
Isobar Pressure A line connecting points of equal or constant pressure.
Isotherm Temperature A line connecting points of equal or constant temperature.
Isotach Wind Speed A line connecting points of equal wind speed.
Isohume Humidity A line drawn through points of equal humidity.
Isodrotherm Dewpoint A line connecting points of equal dewpoint.
A surface chart (also called surface map or sea level pressure chart) is an analyzed chart of surface weather observations. Essentially, a surface chart shows the distribution of sea level pressure (lines of equal pressure are isobars). Hence, the surface chart is an isobaric analysis showing identifiable, organized pressure patterns
The WPC issues surface analysis charts for North America eight times daily, valid at 00, 03, 06, 09, 12, 15, 18, and 21 UTC.
Know chart symbols
Know wind symbols
A freezing level analysis graphic shows the height of the 0°C constant-temperature surface. The initial analysis is updated hourly
Turbulence (Graphical Turbulence Guidance (GTG)) Analysis The NWS produces a turbulence product that is derived from NWS model data with no forecaster modifications. This product is the GTG.
Book
Class
Relative humidity is not amount of water in air, it is amount that temp of air can hold
Higher dew point=more water vapor in air
Surface temp-dew point spread is important in anticipation of fog but has little bearing on precip
Weather balloons at certain centers
Microsoft Flight Sim 2020 you can see updrafts
Lapse rate
Adiabatic
3 degree per 1000 feet
Orographic effects
Appendix A cloud pictures will be exact on midterm
Stable vs unstable air
Absolute, neutral, conditional stability
Virga rain
Bergeron rain
AIM has order of hot for the weather briefs, won’t have classes on those Fridays
Isobar pressure difference bad winds
Cumulus, mature, dissipating
Moisture, lifting force, unstable atmosphere
High: clockwise out, low: counterclockwise in
Dew point is temp where air is saturated
AIRMET in-flight every 6 hours, very important to low
Advection, radiation, upslope, precip fog
Remember different types of radar blockage
Bright band cause radar bad at picking up snow
Manual, automated, augmented
ASOS, AWOS, ATIS
Pirep, Airep,
You can report if forecast is different at all, if forecast not happen when expected, etc
Can say to ATC (critical now) or flight service (Routine)
Do SkySpotter AOPA Certificate for 2 points on Final
TDWR
GOES and POES
Aviation Weather
University of Central Missouri Fall 2024 / Jupp / Aviation Weather Handbook FAA
Websites: Ventusky, Windy, Preduty briefing on weather.gov, awc, asrs on nasa.gov
Quizzes
Book isn’t saving my highlights so we type for now:
Quiz Chapter 8-9
Atmospheric pressure is the force per unit area exerted by the weight of the atmosphere
The aneroid barometer is the type most commonly used by meteorologists and the aviation community
Like most substances, air expands as it becomes warmer and contracts as it cools
Sea level pressure is typically displayed on surface weather charts
The density of an air parcel varies inversely with its volume
The density of an air parcel can be changed by changing its mass pressure, or temperature. Boyle’s Law says that the density of an ideal gas (rho) is given by: rho=MP/RT Where M is the molar mass, P is the pressure, R is the universal gas constant, and T is the absolute temperature
Density is inversely related to temperature
Density of an air parcel is inversely related to its quantity of water vapor
True altitude is the actual vertical distance above MSL
The altimeter setting is the value to which the scale of the pressure altimeter is set so the altimeter indicates true altitude at field elevation
If flying in cold weather over mountainous areas, however, pilot needs to take this difference between indicated and true altitude into account. The pilot needs to know that the true altitude assures clearance of terrain, and compute a correction to indicated altitude
Density altitude is the pressure altitude corrected for temperature deviations from the standard atmosphere
Density altitude is an index to aircraft performance. Higher density altitude decreases aircraft performance. Lower density altitude increases aircraft performance.
Hadley cell- Low-latitude air movement toward the Equator that, with heating, rises vertically with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and subtropical climates
Ferrel cell- A mid-latitude mean atmospheric circulation cell for weather, named by William Ferrel in the 19th century. In this cell, the air flows poleward and eastward near the surface, and equatorward and westward at higher levels
Polar cell- Air rises, diverges, and travels toward the poles. Once over the poles, the air sinks, forming polar highs. At the surface, air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies)
Jet streams follow the boundaries between hot and cold air. Since these hot and cold air boundaries are most pronounced in winter, jet streams are the strongest for both the Northern and Southern Hemisphere winters
Jet streams vary in height from around flight level (FL) 200 to FL450 and can reach speeds of more than 275 miles per hour (mph) 239 knots (kts)
Quiz Chapter 10
Wind is named according to the direction from which it is blowing.
Whenever a pressure difference develops over an area, the Pressure Gradient Force (PGF) makes the wind blow in an attempt to equalize pressure differences.
PGF is directed from higher height/pressure to lower height/pressure and is perpendicular to contours/isobars.
Coriolis force is an apparent force that affects all moving objects. The force deflects air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Friction between the wind and the terrain surface slows the wind.
When a PGF is first established, wind begins to blow from higher to lower heights directly across the height contours. However, the instant air begins moving,Coriolis force deflects it to the right. Soon the wind is deflected a full 90° and is parallel to the height contours. At this time, Coriolis force exactly balances PGF. With the forces in balance, wind will remain parallel to height contours. This is called the geostrophic wind.
In the Northern Hemisphere, the surface wind spirals clockwise and outward from high pressure, and counterclockwise and inward into low pressure.
A sea breeze is a coastal local wind that blows from sea to land and is caused by temperature differences when the sea surface is colder than the adjacent land.
A land breeze is a coastal breeze blowing from land to sea caused by the temperature difference when the sea surface is warmer than the adjacent land.
A valley breeze is a wind that ascends a mountain valley during the day. Air in contact with the sloping terrain becomes warmer (less dense) than air above the valley.
A mountain breeze is the nightly downslope winds commonly encountered in mountain valleys. Air in contact with the sloping terrain cools faster than air above the valley.
A gust is a fluctuation of wind speed with variations of 10 knots (kt) or more between peaks and lulls.
Quiz Chapter 11
Air masses are classified according to the temperature and moisture properties of their source regions.
Temperature Properties • Arctic (A)—An extremely deep, cold air mass that develops mostly in winter over arctic surfaces of ice and snow.
Temperature Properties • Polar (P)—A relatively shallow, cool to cold air mass that develops over high latitudes.
Temperature Properties • Tropical (T)—A warm to hot air mass that develops over low latitudes.
Moisture Properties • Continental (c)—A dry air mass that develops over land.
Moisture Properties • Maritime (m)—A moist air mass that develops over water
Continental Arctic (cA) - Cold, Dry. Continental Polar (cP) - Cold, dry. Continental Tropical (cT) - Hot, dry. Maritime Polar (mP) - Cool, moist. Maritime Tropical (mT) - Warm, moist.
Air Mass Modification - As these air masses move around the Earth, they can begin to acquire different attributes.
Lake effect is the effect of any lake in modifying the weather near its shore and for some distance downwind.
A front is a boundary or transition zone between two air masses. Fronts are classified by which type of air mass (cold or warm) is replacing the other.
A warm front occurs when a warm mass of air advances and replaces a body of colder air. Warm fronts move slowly, typically 10 to 25 mph. The slope of the advancing front slides over the top of the cooler air and gradually pushes it out of the area.
A cold front occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air. It is so dense, it stays close to the ground and acts like a snowplow, sliding under the warmer air and forcing the less dense air aloft. Cold fronts have a steep slope, and the warm air is forced upward abruptly.
A continuous line of thunderstorms, or squall line, may form along or ahead of the front. Squall lines present a serious hazard to pilots as squall-type thunderstorms are intense and move quickly.
When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. This front is called a stationary front. Stationary frontal slope can vary, but clouds and precipitation would still form in the warm rising air along the front.
Cold fronts typically move faster than warm fronts, so in time they catch up to warm fronts. As the two fronts merge, an occluded front forms. At the occluded front, the cold air undercuts the retreating cooler air mass associated with the warm front, further lifting the already rising warm air.
A wave cyclone is a low-pressure circulation that forms and moves along a front. The circulation about the cyclone center tends to produce a wavelike kink along the front.
A dryline is a low-level boundary hundreds of miles long separating moist and dry air masses.
Quiz Chapter 12-15
a bubble or parcel of air ascends (rises), it moves into an area of lower pressure (pressure decreases with height). As this occurs, the parcel expands. This requires energy (or work), which takes heat away from the parcel, so the air cools as it rises.
The lapse rate of a rising, unsaturated parcel (air with relative humidity less than 100 percent) is approximately 3 °C per 1,000 ft (9.8 °C per km). This is called the dry adiabatic lapse rate.
The Lifted Condensation Level (LCL) is the level at which a parcel of moist air lifted dry adiabatically becomes saturated. At this altitude, the temperature-dewpoint spread is zero and relative humidity is 100 percent. Further lifting of the saturated parcel results in condensation, cloud formation, and latent heat release.
Orographic Effects: Winds blowing across mountains and valleys cause the moving air to alternately ascend and descend. If relief is sufficiently great, the resulting expansional cooling and compressional warming of air affects the development and dissipation of clouds and precipitation.
Frontal lift occurs when the cold, denser air wedges under the warm, less dense air, plowing it upward, and/or the warmer air rides up and over the colder air in a process called overrunning. Clouds and precipitation will form given sufficient lift and moisture content of the warm air.
Cirri-form: High-level clouds that form above 20,000 ft (6,000 m) and are usually composed of ice crystals. High-level clouds are typically thin and white in appearance, but can create an array of colors when the Sun is low on the horizon. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.
Nimbo-form: Nimbus comes from the Latin word meaning “rain.” These clouds typically form between 7,000 and 15,000 ft (2,100 to 4,600 m) and bring steady precipitation. As the clouds thicken and precipitation begins to fall, the bases of the clouds tend to lower toward the ground.
Cumuli-form: Clouds that look like white, fluffy cotton balls or heaps and show the vertical motion or thermal uplift of air taking place in the atmosphere. The level at which condensation and cloud formation begins is indicated by a flat cloud base, and its height will depend upon the humidity of the rising air. The more humid the air, the lower the cloud base. The tops of these clouds can reach over 60,000 ft.
Strati-form: Stratus is Latin for “layer” or “blanket.” The clouds consist of a featureless low layer that can cover the entire sky like a blanket, bringing generally gray and dull weather. The cloud bases are usually only a few hundred feet above the ground. Over hills and mountains, they can reach ground level when they may be called fog. Also, as fog lifts off the ground due to daytime heating, the fog forms a layer of low stratus clouds.
Atmospheric stability is the property of the ambient air that either enhances or suppresses vertical motion of air parcels and determines which type of clouds and precipitation a pilot will encounter.
Absolute stability is the state of a column of air in the atmosphere when its lapse rate of temperature is less than the moist adiabatic lapse rate.
Neutral stability is the state of a column of air in the atmosphere in which an ascending (or descending) air parcel always has the same temperature (density) as the surrounding environmental air.
Conditional instability is the state of a column of unsaturated air in the atmosphere when its lapse rate of temperature is less than the dry adiabatic lapse rate, but greater than the moist adiabatic lapse rate. An air parcel lifted upward would be initially stable, but at some point above its Lifting Condensation Level (LCL) it would become unstable.
Daytime heating of the surface increases temperature lapse rates and decreases stability. Conversely, nighttime cooling of the surface decreases temperature lapse rates and increases stability.
The Lifted Index (LI) is the temperature difference between an air parcel (usually at the surface) lifted adiabatically and the temperature of the environment at a given pressure (usually 500 mb) in the atmosphere. A positive value indicates a stable column of air (at the respective pressure), a negative value indicates an unstable column of air, and a value of zero indicates a neutrally stable column of air.
Precipitation formation requires three ingredients: water vapor, sufficient lift to condense the water vapor into clouds, and a growth process that allows cloud droplets to grow large and heavy enough to fall as precipitation.
Two growth processes exist that allow cloud droplets (or ice crystals) to grow large enough to reach the ground as precipitation before they evaporate (or sublimate). One process is called the collision-coalescence, or warm rain process. The other process is called the ice crystal process.
Snow occurs when the temperature remains below freezing throughout the entire depth of the atmosphere.
Ice pellets (sleet) occur when there is a shallow layer aloft with above-freezing temperatures and with a deep layer of below-freezing air based at the surface.
Freezing rain occurs when there is a deep layer aloft with above-freezing temperatures and with a shallow layer of below-freezing air at the surface.
Hail forms when supercooled water droplets above the freezing level begin to freeze. Once a droplet has frozen, other droplets latch on and freeze to it, so the hailstone grows—sometimes into a huge iceball.
The most effective tool to detect precipitation is radar. Radar, which is an acronym that stands for “radio detection and ranging,” has been utilized to detect precipitation since the 1940s.
The radar antenna alternately emits and receives radio waves into the atmosphere. Pulses of energy from the radio waves may strike a target. If they do, part of that energy will return to the antenna.
Range attenuation is automatically compensated for by the WSR-88D. However, most airborne radars only compensate for range attenuation out to a distance of 50 to 75 NM. Targets beyond these ranges will appear less intense than they actually are.
Under normal conditions, the atmosphere’s density gradually decreases with increasing height. As a result, the upper portion of a radar beam travels faster than the lower portion of the beam. This causes the beam to bend downward.
Subrefraction may cause the radar beam to overshoot objects that would normally be detected. For example, distant thunderstorms may not be detected with subrefraction. Subrefraction may also cause radar to underestimate the true strength of a thunderstorm.
Sometimes the density of the atmosphere decreases with height at a less-than-normal rate (actual density is greater than normal) or even increases with height. When this occurs, the radar beam will bend more than normal toward the Earth’s surface. This phenomenon is called superrefraction.
If the atmospheric condition that causes superrefraction bends the beam equal to, or greater than, the Earth’s curvature, then a condition called ducting (or trapping) occurs. When ducting occurs, the radar beam will hit the surface of the Earth, causing some of the beam’s energy to backscatter.
Ground clutter is radar echoes’ returns from trees, buildings, or other objects on the ground. It appears as a roughly circular region of high reflectivity at ranges close to the radar.
Convective precipitation is distinguished by the following radar characteristics:
• Echoes tend to form as lines or cells;
• Reflectivity gradients are strong;
• Precipitation intensities generally vary from moderate to extreme;
• Occasionally, precipitation intensities can be light; and
• Echo patterns change rapidly when animating the image.
Stratiform precipitation has the following radar characteristics:
• Widespread in aerial coverage;
• Weak reflectivity gradients;
• Precipitation intensities are generally light or moderate (39 dBZ or less);
• Occasionally, precipitation intensities can be stronger; and
• Echo patterns change slowly when animating the image.
Bright band is a distinct feature observed by radar that denotes the freezing (melting) level. These particles reflect significantly more energy (appearing to the radar as large raindrops) than the portions of the cloud above and below the freezing layer.
Quiz Chapter 16-17
Strong winds flow over or around mountains or ridges. If the surrounding atmosphere is unstable, the vertical displacement of the air will (if sufficient moisture is present) lead to thunderstorm formation or at least the development of deep convective clouds. However, if the wind is sufficiently strong and the surrounding atmosphere is stable, a wave will develop.
In order for gravity waves to develop, the atmosphere must possess at least some degree of static stability.
Kelvin-Helmholtz (K-H) instability induced by the wind shear associated with strong winds aloft is likely the chief source of high-level turbulence away from mountain ranges (Clear Air Turbulence (CAT).
Mountain Waves are air that is moving nearly perpendicular to the barrier is deflected upward and accelerated as it passes over the crests and down the lee slopes of the terrain.
Trapped Lee Waves are a type of mountain wave that propagates a train of Altocumulus Standing Lenticular (lens- or airfoil-shaped clouds) extending far downwind of the mountain (although trapped lee waves frequently occur without clouds).
When mountain waves are present, it is quite common for a rotor zone to develop near or below ridge level on the downwind side of the mountain, under a wave crest and associated lenticular cloud (if sufficient moisture is present). This is an area of potentially severe-to-extreme wind shear and turbulence.
Occasionally, an extremely strong low-level temperature inversion can occur in mountainous areas, with the inversion top below ridge level (perhaps 900 to 1,000 ft AGL) and a pool of very cold air at the surface. If this phenomenon occurs with strong wind flow above the inversion layer, there will be a concentrated shear zone near the inversion, which can lead to both significant turbulence encounters and abrupt airspeed changes for aircraft that penetrate the inversion on climbout or during descent.
There are at least two primary causes of boras: 1) cold fronts aligned parallel to the mountain range and moving perpendicular to it, with the cold air eventually spilling over; and 2) cold outflow, from thunderstorms over or near a mountain range, that builds up to sufficient depth to spill over and down the opposite slope.
The trade winds converge in the vicinity of the equator where air rises. This convergence zone is referred to as the Intertropical Convergence Zone (ITCZ).
The subtropical highs shift southward during the Northern Hemisphere winter and northward during summer.
Continental Weather Along the west coasts of continents under a subtropical high, the air is stable. The inversion is strongest and lowest where the east side of the subtropical high-pressure area overlies the west side of a continent. The extreme southwestern United States, for example, is dominated in summer by a subtropical high
On eastern continental coasts the inversion is weakest and highest where the west side of the subtropical high-pressure area overlies the eastern coast of a continent. Convection can penetrate the inversion, and showers and thunderstorms often develop.
Trade winds blowing out of the subtropical highs over ocean areas are predominantly northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.
Many islands in the trade wind belt have lush vegetation and even rain forests on the windward side, while the leeward is semiarid.
Convection in the Intertropical Convergence Zone (ITCZ) carries huge quantities of moisture to great heights. Showers and thunderstorms frequent the ITCZ, and tops to 40,000 ft or higher are common.
Over the large land mass of Asia, an intense high during the winter and a well-developed low during the summer. The cold, high pressures in winter cause wind to blow from the deep interior outward and offshore. In summer, wind direction reverses, and warm moist air is carried far inland into the low-pressure area. This large-scale seasonal wind shift is the monsoon. The most notable monsoon is that of southern and southeastern Asia.
A shear line, results when a semipermanent high splits into two cells, inducing a trough. These shear lines are zones of convergence creating forced upward motion. Consequently, considerable thunderstorm and rain shower activity occurs along a shear line.
Tropical Upper Tropospheric Trough (TUTT) generally at or above 10,000 ft, move through the Tropics, especially along the poleward fringes. These are known as TUTTs. As a TUTT moves to the southeast or east, it spreads middle and high cloudiness over extensive areas to the east of the trough line.
On occasion, a line of convection similar to a squall line moves westward off the continent at tropical latitudes into the oceanic trade winds. In the North Atlantic, this is known as the West African Disturbance Line (WADL). A WADL can move faster than easterly waves at 20 to 40 mph. Some WADLs eventually develop into tropical storms or hurricanes.
“Tropical cyclone” is a general term for any low that originates over tropical oceans. Tropical cyclones are classified according to their intensity based on the average wind speeds.
Over the north Atlantic and northeast Pacific Oceans, tropical cyclone classifications are:
Tropical Depression —sustained winds up to 34 kt (64 km/h).
Tropical Storm—sustained winds of 35 to 64 kt (65 to 119 km/h).
Hurricane—sustained winds of at least 65 kt (120 km/h) or more.
Tropical cyclones are unlikely within 5° of the Equator because the coriolis force is so small near the Equator that it will not turn the winds enough for them to flow around a low-pressure area.
Most tropical cyclones that form eyes do so within 48 hours of the cyclone reaching tropical storm strength. In the eye, skies are free of turbulent cloudiness, and wind is comparatively light.
Level 3
Most newer mobile homes will sustain severe damage with potential for complete roof failure and wall collapse. Poorly constructed frame homes can be destroyed by the removal of the roof and exterior walls. Unprotected windows will be broken by flying debris. Well-built frame homes can experience major damage involving the removal of roof decking and gable ends.
Level 2
Poorly constructed frame homes have a high chance of having their roof structures removed, especially if they are not anchored properly. Unprotected windows will have a high probability of being broken by flying debris. Well-constructed frame homes could sustain major roof and siding damage. Failure of aluminum, screened-in, swimming pool enclosures will be common
Level 5
.A high percentage of frame homes will be destroyed, with total roof failure and wall collapse. Extensive damage to roof covers, windows, and doors will occur.
Level 4
Poorly constructed frame homes can sustain complete collapse of all walls as well as the loss of the roof structure. Well-built homes also can sustain severe damage with loss of most of the roof structure and/or some exterior walls.
Level 1
Newer mobile homes that are anchored properly can sustain damage involving the removal of shingle or metal roof coverings, and loss of vinyl siding, as well as damage to carports, sunrooms, or lanais. Some poorly constructed frame homes can experience major damage, involving loss of the roof covering and damage to gable ends, as well as the removal of porch coverings and awnings.
Quiz Chapter 18-21
Fog forms when the temperature and dewpoint of the air become identical (or nearly so). This may occur through cooling of the air to its dewpoint (producing radiation fog, advection fog, or upslope fog), or by adding moisture and thereby elevating the dewpoint (producing frontal fog or steam fog).
Fog types are named according to their formation mechanism.
Radiation fog is a common type of fog, produced over a land area when radiational cooling reduces the air temperature to or below its dewpoint.
Advection fog forms when moist air moves over a colder surface and the subsequent cooling of that air to below its dewpoint.
Upslope fog forms as a result of moist, stable air being adiabatically cooled to or below its dewpoint as it moves up sloping terrain
When warm, moist air is lifted over a front, clouds and precipitation may form. If the cold air below is near its dewpoint, evaporation (or sublimation) from the precipitation may saturate the cold air and form fog
Steam Fog When very cold air moves across relatively warm water, enough moisture may evaporate from the water surface to produce saturation.
Freezing fog occurs when the temperature falls to 32 °F (0 °C) or below. Tiny, supercooled liquid water droplets in fog can freeze instantly on exposed surfaces when surface temperatures are at or below freezing.
Mist is a visible aggregate of minute water droplets or ice crystals suspended in the atmosphere that reduces visibility to less than 7 sm (11 km), but greater than, or equal to, 5/8 sm (1 km).
Haze is a suspension in the air of extremely small particles invisible to the naked eye and sufficiently numerous to give the air an opalescent appearance. It reduces visibility by scattering the shorter wavelengths of light
Smoke is a suspension in the air of small particles produced by combustion due to fires, industrial burning, or other sources.
Blowing snow is snow lifted from the surface of the Earth by the wind to a height of 6ft (2 m) or more above the ground, and blown about in such quantities that the reported horizontal visibility is reduced to less than 7 sm
A dust storm is a severe weather condition characterized by strong winds and dust-filled air over an extensive area. Dust storms originate over regions when fine-grained soils, rich in clay and silt, are exposed to strong winds and lofted airborne.
A sandstorm is particles of sand carried aloft by a strong wind. The sand particles are mostly confined to the lowest 10 ft (3.5 m), and rarely rise more than 50 ft (15 m) above the ground. Sandstorms are similar to dust storms, but occur on a localized scale.
A haboob is a dust storm or sandstorm that forms as cold downdrafts from a thunderstorm turbulently lift dust and sand into the air. While haboobs are often short-lived, they can be quite intense. The dust wall may extend horizontally for more than 60 mi (100 km) and rise vertically to the base of the thunderstorm
Volcanic ash is made up of fine particles of rock powder that originate from a volcano and that may remain suspended in the atmosphere for long periods. Severe volcanic eruptions that send ash into the upper atmosphere occur somewhere around the world several times per year.
Stratus is the most frequent cloud associated with low ceilings. Stratus clouds, like fog, are composed of extremely small water droplets or ice crystals suspended in air.
Convective turbulence is turbulent vertical motions that result from convective currents and the subsequent rising and sinking of air. For every rising current, there is a compensating downward current.
When the air is too dry for cumuliform clouds to form, convective currents can still be active. This is called dry convection, or thermals. A pilot has little or no indication of their presence until encountering the turbulence.
Turbulence is present in all thunderstorms, and severe or extreme turbulence is common. A severe thunderstorm can destroy an aircraft. Gust loads can be severe enough to stall an aircraft at maneuvering speed or to cause structural damage at cruising speed. The strongest turbulence within the cloud occurs between updrafts and downdrafts.
Mechanical turbulence is turbulence caused by obstructions to the wind flow, such as trees, buildings, mountains, and so on
Strong wind shears often occur across temperature inversion layers, which can generate turbulence
One of the principal areas where Clear Air Turbulence (CAT) is found is in the vicinity of the jet streams.
Nonconvective LLWS is defined as a wind shear of 10 kt or more per 100 ft in a layer more than 200 ft thick that occurs within 2,000ft of the surface.
Pure water suspended in the air does not freeze until it reaches a temperature of -40 °C. This occurs because surface tension of the droplets inhibits freezing.
Rime ice is rough, milky, and opaque ice formed by the instantaneous freezing of small, supercooled water droplets after they strike the aircraft. It is the most frequently reported icing type.
Clear ice (or glaze ice) is a glossy, clear, or translucent ice formed by the relatively slow freezing of large, supercooled water droplets. Clear icing conditions exist more often in an environment with warmer temperatures, higher liquid water contents, and larger droplets.
Supercooled Large Drops (SLD) A type of clear icing that is especially dangerous to flight operations is ice formed from SLDs. These are water droplets in a subfreezing environment with diameters larger than 40 microns, such as freezing drizzle (40 to 200 microns) and freezing rain (>200 microns).
Mixed ice is a mixture of clear ice and rime ice
Supercooled Liquid Water Content (SLWC) is important in determining how much water is available for icing. The highest quantities can be found in cumuliform clouds, with the lowest quantities found in stratiform clouds. However, in most icing cases, SLWC is low.
The only physical cold limit to icing is at -40 °C because liquid droplets freeze without nuclei present.
Most icing reports occur in the vicinity of fronts.
Icing with mountains can be especially hazardous because a pilot may be unable to descend to above-freezing temperatures due to terrain elevation
Structural icing degrades an aircraft’s performance. It destroys the smooth flow of air, increasing drag while decreasing the ability of the airfoil to create lift. The actual weight of ice on an airplane is insignificant when compared to the airflow disruption it causes.
Any point north of the Arctic Circle has autumn and winter days when the Sun stays below the horizon all day and has spring and summer days with 24 hours of sunshine when the Sun stays above the horizon.
Quiz Chapter 22-23
A thunderstorm is a local storm, invariably produced by a cumulonimbus (CB) cloud, and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes hail.
Thunderstorm cell formation needs three ingredients: sufficient water vapor, unstable air, and a lifting mechanism.
A thunderstorm cell is the convective cell of a cumulonimbus cloud having lightning and thunder. It undergoes three distinct stages during its life cycle: towering cumulus, mature, and dissipating.
The distinguishing feature of the towering cumulus stage is a strong convective updraft.
The cell transitions to the mature stage when precipitation reaches the surface.
The dissipating stage is marked by a strong downdraft embedded within the area of precipitation. Subsiding air replaces the updraft throughout the cloud, effectively cutting off the supply of moisture provided by the updraft.
There are three principal thunderstorm types: single-cell, multicell (cluster and line), and supercell.
With an organized multicell cluster, as the first cell matures, it is carried downwind, and a new cell forms upwind to take its place. A multicell cluster may have a lifetime of several hours (or more). New cells will continue to form as long as the three necessary ingredients exist.
A supercell thunderstorm is an often dangerous, long-lived convective storm that consists primarily of a single, quasi-steady rotating updraft that persists for an extended period of time. It has a very organized internal structure that enables it to produce especially dangerous weather for pilots who encounter them. Updraft speeds may reach 9,000 fpm (100 kt).
Storm motion equals the combined effects of both advection and propagation.
Derecho is a widespread, long-lived, straight-line windstorm that is associated with a fast-moving band of severe thunderstorms.
While not every thunderstorm contains all hazards, it is not possible to visually determine which hazards a thunderstorm contains. Hazards include: low ceiling and visibility, lightning, adverse winds, downbursts, turbulence, icing, hail, rapid altimeter changes, static electricity, tornadoes, and engine water ingestion.
Every thunderstorm produces lightning and thunder by definition. Lightning is a visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between a cloud and air, between a cloud and the ground, or between the ground and a cloud.
Downbursts can create hazardous conditions for pilots and have been responsible for many LLWS accidents. Smaller, shorter-lived downbursts are called microbursts.
It is vital for pilots to recognize that some microbursts cannot be successfully escaped with any known techniques. Some wind shears that are within the performance capability of the aircraft have caused accidents.
Vertical winds exist in every microburst and increase in intensity with altitude. Such winds usually reach peak intensity at heights greater than 500 ft above the ground. Downdrafts with speeds greater than 3,000 fpm can exist in the center of a strong microburst.
Pressure usually falls rapidly with the approach of a thunderstorm. Pressure then usually rises sharply with the onset of the first gust and arrival of the cold downdraft and heavy rain, falling back to normal as the thunderstorm passes.
The corona discharge is weakly luminous and may be seen at night. Although it has a rather eerie appearance, it is harmless. It was named “St. Elmo’s Fire” by Mediterranean sailors, who saw the brushy discharge at the top of ship masts.
The most violent thunderstorms draw air into their cloud bases with great force. If the incoming air has any initial rotating motion, it often forms an extremely concentrated vortex from the surface well into the cloud.
Enhanced Fujita Scale
EF-0 (65-85mph),
EF-1 (86-110mph),
EF-2 (111-135mph),
EF-3 (135-165mph),
EF-4 (166-200mph),
EF-5 (>200mph)
Over 80 percent of all tornadoes in the United States are produced by supercell thunderstorms.
It is important to note that while hail always gives a radar echo, it may fall several miles from the nearest visible cloud, and hazardous turbulence may extend to as much as 20 mi from the echo edge.
Avoid by at least 20 miles any thunderstorm identified as severe or giving an intense, heavy, or extreme radar echo.
Do not turn back once in the thunderstorm. A straight course through the storm most likely will get the aircraft out of the hazards most quickly. In addition, turning maneuvers increase stress on the aircraft.
The Sun is the dominant source of the conditions commonly described as space weather. Emissions from the Sun are both continuous (e.g., solar luminescence and solar wind) and eruptive (e.g., coronal mass ejections (CME) and flares). These solar eruptions may cause radio blackouts, magnetic storms, ionospheric storms, and radiation storms at Earth.
The Sun is a variable star. That means the balance between the continuous emissions and the eruptive emissions changes with time. One metric that is commonly used to track this variability is the occurrence of sunspots.
Earth’s magnetic field extends outward in all directions. This forms a cocoon for the planet, protecting it from the flow of the solar wind. The cocoon is called the magnetosphere.
The most visible manifestation of the energy being absorbed from the solar wind into the magnetosphere is the aurora, both in the Northern and Southern Hemispheres. The aurora occurs when accelerated electrons from the Sun follow the magnetic field of Earth down to the polar regions, where they collide with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere.
The symptoms of an ionospheric storm include enhanced currents, turbulence and wave activity, and a nonhomogeneous distribution of free electrons. This clustering of electrons, which leads to scintillation of signals passing through the cluster, is particularly problematic for the Global Navigation Satellite System (GNSS), which includes the United States’ GPS.
Solar radiation storms occurring under particular circumstances cause an increase in radiation dose to flight crews and passengers. As high polar latitudes and high altitudes have the least shielding from the particles, the threat is the greatest for higher altitude polar flights.
Quiz Chapter 24.1-35
Observations are weather data collected automatically by sensor(s), manually by trained weather observers, or by a combination of both, and are the basic information upon which forecasts and advisories are made in support of a wide range of weather-sensitive activities within the public and private sectors, including aviation.
Manual surface weather observations are made by a human weather observer who is certified by the FAA.
Automated observations are derived from instruments and algorithms without human input or oversight.
Augmented Observation are the addition of human observers to report weather elements that are beyond the capabilities of the automated system and/or are deemed operationally significant.
AWOS generates a METAR at 20-minute intervals and does not report SPECIs. AWOS also provides OMOs available by phone or radio.
METARs are sometimes referred to as “hourly” reports since they are routinely produced near the top of the hour.
A SPECI is an unscheduled report taken when any of the criteria given in Table 24-2 are observed during the period between hourly reports. SPECIs contain all data elements found in a METAR. All SPECIs are issued as soon as possible when relevant criteria are observed.
The station identifier, in ICAO format, is included in all reports to identify the station to which the coded report applies. The ICAO airport code is a four-letter alphanumeric code designating each airport around the world.
The coded time of observations is the actual time of the report, or when the criteria for a SPECI is met or noted. The date and time group always ends with a Z, indicating Zulu time (or Coordinated Universal Time (UTC)).
In the wind group, the wind direction is coded as the first three digits and is determined by averaging the recorded wind direction over a 2-minute period. Immediately following the wind direction is the wind speed coded in two or three digits. Wind speed is determined by averaging the speed over a 2-minute period and is coded in whole knots using the units, tens digits, and, when appropriate, the hundreds digit.
The visibility group is coded as the surface visibility in statute miles. A space is coded between whole numbers and fractions of reportable visibility values. The visibility group ends with SM to indicate that the visibility is in statute miles. For example, a visibility of 1½ sm is coded 1 1/2SM. U.S. automated stations use an M to indicate “less than.” For example, M1/4SM means a visibility of less than ¼ sm
The Runway Visual Range (RVR) is an instrument-derived value representing the horizontal distance a pilot may see down the runway. RVR is reported whenever the station has RVR equipment and prevailing visibility is 1 sm or less, and/or the RVR for the designated instrument runway is 6,000 ft or less
Obscuration Reporting (METAR Codes)
Weather phenomena occurring beyond the point of observation (between 5 and 10 sm) are coded as in the vicinity (VC).
Precipitation Types (METAR Codes)
The sky condition group is based on the amount of cloud cover (the first three letters) followed by the height of the base of the cloud cover (final three digits). The height of the layer is recorded in feet AGL.
The altimeter group always starts with an A and is followed by the four-digit group representing the pressure in tens, units, tenths, and hundredths of inches of mercury
Type of Automated Station AO1 or AO2 is coded in all METARs/SPECIs from automated stations. Automated stations without a precipitation discriminator are identified as AO1; automated stations with a precipitation discriminator are identified as AO2.
When lightning is detected by an automated system: • Within 5 NM of the Airport Location Point (ALP), it is reported as TS in the body of the report with no remark.
Beginning and Ending of Precipitation At designated stations, the beginning and ending times of precipitation are coded in the following format: the type of precipitation, followed by either a B for beginning or an E for ending, and the time of occurrence.
If the pressure is rising or falling at a rate of at least 0.06 in per hour and the pressure change totals 0.02 in or more at the time of the observation, a pressure change remark is reported. When the pressure is rising or falling rapidly at the time of observation, the remark pressure rising rapidly (PRESRR) or pressure falling rapidly (PRESFR) is included in the remarks.
A maintenance indicator ($) is coded when an automated system detects that maintenance is needed on the system.
Pilot Weather Reports (PIREP) Pilots can report any observation, good or bad, to assist other pilots with flight planning and preparation. If conditions were forecasted to occur but not encountered, a pilot can also report the observed condition.
Urgent (UUA) PIREPs contain information about:
• Tornadoes, funnel clouds, or waterspouts;
• Severe or extreme turbulence (including CAT);
• Severe icing;
• Hail;
• LLWS within 2,000 ft of the surface (LLWS PIREPs are classified as UUA if the pilot reports air speed fluctuations of 10 kt or more; or if air speed fluctuations are not reported but LLWS is reported, the PIREP is classified as UUA);
• Volcanic ash clouds; and/or
• Any other weather phenomena reported that are considered by the air traffic controller or Flight Service specialist receiving the report as being hazardous, or potentially hazardous, to flight operations
Pilot Weather Reports: Turbulence intensity, type, and altitude are reported after wind direction and speed. Duration (intermittent (INTMT), occasional (OCNL), or continuous (CONS)) is coded first (if reported by the pilot), followed by the intensity (light (LGT), moderate (MOD), severe (SEV), or extreme (EXTRM)). Range or variation of intensity is separated with a hyphen (e.g., MOD-SEV). If turbulence was forecast, but not encountered, negative (NEG) is entered
Pilot Weather Reports: Icing intensity, type, and altitude are reported after turbulence. Intensity is coded first using contractions TRACE, light (LGT), moderate (MOD), or severe (SEV). Reports of a range or variation of intensity is separated with a hyphen. If icing was forecast but not encountered, negative (NEG) is coded. Icing type is reported second. Reportable types are RIME, clear (CLR), or mixed (MX).
AIREPs are messages from an aircraft to a ground station
Midterm
Chapter 24.36-60, 25 Quiz
Modern commercial aircraft are equipped with meteorological sensors and associated sophisticated data acquisition and processing systems. These systems continuously record meteorological information on the aircraft and send these observations at selected intervals to ground stations via satellite or radio links where they are processed and disseminated.
WSR-88D radars are continuously generating radar observations. Each radar observation, called a volume scan, consists of 5 to 14 separate elevation “tilts,” and takes between 4 and 11 minutes to generate, depending on the radar’s mode of operation.
The WSR-88D radar network consists of 160 radars operated by the NWS, FAA, and DOD.
The WSR-88D is operated in Precipitation Mode when precipitation is present, although some nonprecipitation echoes can still be detected in this operating mode. The NWS uses Precipitation Mode to see higher into the atmosphere when precipitation is occurring to analyze the vertical structure of the storms. The faster rotation of the WSR-88D in Precipitation Mode allows images to update at a faster rate, approximately every 4 to 6 minutes.
WSR-88D radar reflectivity is correlated to intensity of precipitation. For example, in Precipitation Mode, when the decibel value reaches 15, light precipitation is present. The higher the indicated reflectivity value, the higher the rainfall rate
A radar mosaic consists of multiple single-site radar images combined to produce a radar image on a regional or national scale
Composite Reflectivity is the maximum echo intensity (reflectivity) detected within a column of the atmosphere above a location. During its tilt sequence, the radar scans through all of the elevation slices to determine the highest decibel value in the vertical column, then displays that value on the product
The Base Reflectivity product is a display of both the location and intensity of reflectivity data from the lowest elevation angle scan, or 0.5º above the horizon. Base Reflectivity is also known as “Lowest Tilt” and “Reflectivity at Lowest Altitude,” depending on the website or weather data service provider
The terminal Doppler weather radar (TDWR) is a Doppler weather radar system operated by the FAA, which is used primarily for the detection of hazardous wind shear conditions, precipitation, and winds aloft on and near major airports situated in climates with great exposure to thunderstorms
GeoColor imagery is a multispectral product composed of true color (using a simulated green component) during the daytime, and an IR product at night. During the day, the imagery looks approximately as it would appear when viewed with human eyes from space.
Visible imagery displays reflected sunlight from the Earth’s surface, clouds, and particulate matter in the atmosphere. Visible satellite images, which look like black and white photographs, are derived from the satellite signals.
IR images display temperatures of the Earth’s surface, clouds, and particulate matter.
Water vapor imagery displays the quantity of water vapor generally located in the middle and upper troposphere within the layer between 700 mb (approximately 10,000 ft MSL) and 200 mb (approximately FL390). The most useful information to be gained from the water vapor images is the locations and movements of weather systems, jet streams, and thunderstorms.
“POES” stands for the Polar Operational Environment Satellites. Polar satellites are not stationary. They track along various orbits around the poles
The radiosonde is a small, expendable instrument package (weighing 100 to 500 g), which consists of radio gear and sensing elements, that is suspended below a large balloon inflated with hydrogen or helium gas.
Weather balloons with radiosondes are launched twice a day worldwide from designated locations at around 1100 UTC and 2300 UTC. It takes approximately 90 minutes for the balloon to reach an altitude of 100,000 ft.
Visual Weather Observation System (VWOS), which is available on the FAA’s Aviation Weather Camera Network, is an advanced camera system that is comprised of a suite of weather sensors and 360-degree camera images that collectively observe and report several critical data fields, including winds, cloud height, visibility, present weather, temperature, dewpoint, and pressure.
Surface weather charts depict weather on a constant-altitude (usually sea level) surface, while upper air charts depict weather on constant-pressure surfaces.
Analysis is the drawing and interpretation of the patterns of various elements on a weather chart. Computers cannot interpret what they analyze. Thus, many meteorologists still perform a subjective analysis of weather charts when needed.
Isobar Pressure A line connecting points of equal or constant pressure.
Isotherm Temperature A line connecting points of equal or constant temperature.
Isotach Wind Speed A line connecting points of equal wind speed.
Isohume Humidity A line drawn through points of equal humidity.
Isodrotherm Dewpoint A line connecting points of equal dewpoint.
A surface chart (also called surface map or sea level pressure chart) is an analyzed chart of surface weather observations. Essentially, a surface chart shows the distribution of sea level pressure (lines of equal pressure are isobars). Hence, the surface chart is an isobaric analysis showing identifiable, organized pressure patterns
The WPC issues surface analysis charts for North America eight times daily, valid at 00, 03, 06, 09, 12, 15, 18, and 21 UTC.
Know chart symbols
Know wind symbols
A freezing level analysis graphic shows the height of the 0°C constant-temperature surface. The initial analysis is updated hourly
Turbulence (Graphical Turbulence Guidance (GTG)) Analysis The NWS produces a turbulence product that is derived from NWS model data with no forecaster modifications. This product is the GTG.
Book
Class
Relative humidity is not amount of water in air, it is amount that temp of air can hold
Higher dew point=more water vapor in air
Surface temp-dew point spread is important in anticipation of fog but has little bearing on precip
Weather balloons at certain centers
Microsoft Flight Sim 2020 you can see updrafts
Lapse rate
Adiabatic
3 degree per 1000 feet
Orographic effects
Appendix A cloud pictures will be exact on midterm
Stable vs unstable air
Absolute, neutral, conditional stability
Virga rain
Bergeron rain
AIM has order of hot for the weather briefs, won’t have classes on those Fridays
Isobar pressure difference bad winds
Cumulus, mature, dissipating
Moisture, lifting force, unstable atmosphere
High: clockwise out, low: counterclockwise in
Dew point is temp where air is saturated
AIRMET in-flight every 6 hours, very important to low
Advection, radiation, upslope, precip fog
Remember different types of radar blockage
Bright band cause radar bad at picking up snow
Manual, automated, augmented
ASOS, AWOS, ATIS
Pirep, Airep,
You can report if forecast is different at all, if forecast not happen when expected, etc
Can say to ATC (critical now) or flight service (Routine)
Do SkySpotter AOPA Certificate for 2 points on Final
TDWR
GOES and POES
