Stage 2

What are the four 'shells' / layers of the atmosphere from lowest to highest?

Troposphere, Stratosphere, Mesosphere, Thermosphere. Nearly all weather occurs in the troposphere.

What is the standard (ISA) sea-level temperature and pressure?

59 degF (15 degC) and 29.92 in Hg (1013.2 mb).

What is the standard temperature lapse rate?

About 2 degC (3.5 degF) per 1,000 ft of altitude gain in the troposphere.

What is the standard pressure lapse rate?

About 1 in Hg per 1,000 ft in the lower atmosphere.

What ultimately causes all weather?

Uneven heating of the Earth's surface by the sun, which creates pressure differences and air movement.

What three things does the atmosphere primarily consist of?

About 78% nitrogen, 21% oxygen, and 1% other gases including water vapor.

What is the Coriolis force and how does it affect wind?

An apparent force from Earth's rotation that deflects moving air to the right in the Northern Hemisphere. It balances against pressure gradient force to create wind flow.

Describe the three-cell global circulation pattern.

Each hemisphere has Hadley, Ferrel, and Polar cells that redistribute heat from equator to poles, producing prevailing wind belts (trade winds, prevailing westerlies, polar easterlies).

Why does wind generally flow clockwise around a high and counterclockwise around a low (Northern Hemisphere)?

Air moves from high to low pressure (pressure gradient force) but is deflected right by Coriolis, resulting in clockwise outflow around highs and counterclockwise inflow around lows.

What weather is generally associated with high pressure vs low pressure?

High pressure: descending air, generally fair/stable weather. Low pressure: rising air, clouds, precipitation, and unstable weather.

What is a sea breeze and when does it occur?

A daytime wind blowing from the cooler sea toward warmer land, because land heats faster than water.

What is a land breeze and when does it occur?

A nighttime wind blowing from cooler land toward warmer water, because land cools faster than water.

What is atmospheric stability?

The atmosphere's resistance to vertical motion. Stable air resists rising; unstable air enhances vertical movement.

What conditions indicate STABLE air?

Stratiform clouds, smooth air, poor visibility (haze/smoke trapped), steady precipitation, and fog. Caused by a small temperature lapse rate.

What conditions indicate UNSTABLE air?

Cumuliform clouds, turbulence, good visibility, showery precipitation, and gusty winds. Caused by a large (steep) temperature lapse rate.

What is a temperature inversion?

A layer where temperature increases with altitude (opposite of normal). It is very stable and often traps haze, fog, and pollutants beneath it.

Where do surface-based temperature inversions commonly form?

On clear, calm nights with light wind as the ground cools rapidly by radiation, cooling the air just above it.

What is relative humidity?

The ratio of water vapor actually in the air to the maximum the air can hold at that temperature, expressed as a percentage.

What is the dewpoint?

The temperature to which air must be cooled (at constant pressure) to become saturated (100% relative humidity).

What does a small temperature/dewpoint spread indicate?

Air is near saturation - high probability of fog, low clouds, or precipitation. As the spread narrows, visibility-restricting weather becomes more likely.

What rule of thumb relates dewpoint spread to cloud bases?

Convective cloud bases (AGL) ~ 1,000 ft for every ~4.4 degF (2.5 degC) of temperature/dewpoint spread at the surface.

Name the three requirements for clouds (or fog) to form.

Water vapor, condensation nuclei, and cooling of the air to its dewpoint.

What is the difference between fog and a cloud?

They are the same phenomenon - fog is simply a cloud with its base at or very near the surface.

Name the main types of fog.

Radiation fog, advection fog, upslope fog, steam fog, and precipitation-induced (frontal) fog.

How does radiation fog form?

On clear, calm nights as the ground cools by radiation, cooling adjacent air to the dewpoint. Common in low/valley areas; burns off with daytime heating.

How does advection fog form?

When warm, moist air moves horizontally over a cooler surface, cooling to its dewpoint. Needs wind and can persist; common in coastal areas.

How does upslope fog form?

When moist, stable air is forced up sloping terrain and cools adiabatically to its dewpoint.

What are the four families of clouds by height?

Low, middle, high, and clouds with extensive vertical development (towering cumulus / cumulonimbus).

What does the prefix/suffix 'nimbo-' or '-nimbus' indicate on a cloud?

A rain-bearing cloud (precipitation).

What cloud type is a sign of instability and possible thunderstorms?

Cumuliform clouds, especially towering cumulus and cumulonimbus.

What are the four forms of precipitation requirements?

Precipitation requires clouds with sufficient water vapor and a means to grow droplets large enough to fall (coalescence or ice-crystal process).

What is an air mass?

A large body of air with fairly uniform temperature and moisture, taking on the characteristics of its source region.

What is a front?

The boundary or transition zone between two air masses of different temperature, humidity, and density.

What are the four types of fronts?

Cold front, warm front, stationary front, and occluded front.

What weather is typical of a fast-moving cold front?

Cumuliform clouds, showers/thunderstorms, gusty turbulent winds, sharp temperature drop, and quickly improving weather after passage.

What weather is typical of a warm front?

Stratiform clouds, steady precipitation, poor visibility, and gradual clearing; warmer temperatures after passage.

What general changes occur in wind, temperature, and pressure as ANY front passes?

Wind shifts (veers), temperature changes, and pressure stops falling and begins to rise after passage.

What is an occluded front?

Forms when a fast cold front overtakes a warm front. Can be cold-type or warm-type occlusion, producing a mix of warm- and cold-front weather.

What three ingredients are required for a thunderstorm to form?

Sufficient water vapor (moisture), an unstable lapse rate (instability), and a lifting force (lifting action).

What are the three stages of a thunderstorm?

Cumulus (building, updrafts), Mature (updrafts AND downdrafts, heaviest weather - most hazardous), and Dissipating (downdrafts dominate).

What signals the beginning of the mature stage of a thunderstorm?

Precipitation beginning to fall at the surface, indicating downdrafts have developed alongside updrafts.

What is an embedded thunderstorm and why is it dangerous?

A thunderstorm obscured by surrounding clouds/stratiform layers. It cannot be seen and avoided visually, making it especially hazardous in IMC.

What is a squall line?

A non-frontal band of active thunderstorms, often ahead of a cold front; frequently severe and difficult to circumnavigate.

How far should you stay from a thunderstorm?

At least 20 nautical miles from any severe or growing thunderstorm, especially those with tops above 35,000 ft.

What are the categories/intensities of turbulence?

Light, Moderate, Severe, and Extreme.

What are the four main causes of turbulence?

Convective (thermal), mechanical (obstructions/terrain), wind shear, and frontal/wake turbulence.

What is clear air turbulence (CAT)?

Turbulence occurring in cloud-free air, often near the jet stream at high altitudes; not detectable visually or by radar.

What is wake turbulence and what produces it?

Wingtip vortices generated by a wing producing lift. Greatest behind large, heavy, clean (no flaps/gear), and slow aircraft.

How should you avoid wake turbulence on landing behind a larger aircraft?

Stay at or above the larger aircraft's flight path and land beyond its touchdown point.

How should you avoid wake turbulence on takeoff behind a larger aircraft?

Rotate before the larger aircraft's rotation point and climb above/upwind of its flight path.

What is wind shear?

A sudden, drastic change in wind speed and/or direction over a short distance. Can occur at any altitude and is extremely hazardous near the ground.

What is a microburst?

A small, intense downdraft (downburst) that produces severe wind shear. Can cause a sudden loss of airspeed and altitude; especially dangerous on takeoff/landing.

Where can low-level wind shear be expected?

Near thunderstorms/microbursts, frontal zones, temperature inversions, and around terrain/buildings.

What are the conditions required for structural icing?

Visible moisture (clouds/precipitation) and an aircraft surface temperature at or below freezing (0 degC).

Name the types of structural icing.

Rime ice, clear (glaze) ice, and mixed ice. Frost is also a form of icing.

What is rime ice?

Rough, milky, opaque ice from small supercooled droplets freezing rapidly; forms in stratiform clouds/light drizzle.

What is clear (glaze) ice?

Smooth, hard, heavy, transparent ice from large supercooled droplets; forms in cumuliform clouds/freezing rain. Most dangerous type.

Why is frost hazardous and what must be done before flight?

Frost disrupts smooth airflow over the wing, increasing stall speed and reducing lift/control. It must be removed before flight (do not take off with frost on the wings).

What is freezing rain a sign of, and why is it dangerous?

Warmer air aloft (a temperature inversion) with below-freezing air below. It produces rapid, heavy clear ice accumulation.

Name common restrictions to visibility.

Fog, haze, smoke, precipitation, blowing snow/dust, and volcanic ash.

Why is volcanic ash hazardous to aircraft?

It can cause engine flameout, sandblast/abrade surfaces and windscreens, clog systems, and contaminate the aircraft. Avoid ash clouds entirely.

What is a METAR?

Aviation Routine Weather Report - an observation of current surface weather at an airport, normally issued hourly.

What is a SPECI?

A special (unscheduled) METAR issued when conditions change significantly between routine hourly observations.

In a METAR, what does the 'Z' after the date/time group mean?

Time is in Zulu (Coordinated Universal Time / UTC). Example: 121753Z = 12th day, 1753 UTC.

How are wind direction and speed coded in a METAR?

Five digits: first three are direction (true north) and last two are speed in knots, followed by KT. Example: 24016KT = from 240 deg at 16 kt. 'G' indicates gusts.

What does 'VRB' mean in the wind group of a METAR?

Wind direction is variable (usually with speeds of 6 kt or less, or thunderstorm conditions).

How is visibility reported in a US METAR?

In statute miles, followed by 'SM'. Example: 10SM = 10 statute miles.

How are clouds coded in a METAR (sky condition)?

By coverage and height in hundreds of feet AGL: SKC/CLR (clear), FEW, SCT (scattered), BKN (broken), OVC (overcast). Example: BKN025 = broken at 2,500 ft AGL.

What defines a 'ceiling'?

The height AGL of the lowest BROKEN or OVERCAST layer, or vertical visibility into an obscuration.

How is temperature and dewpoint coded in a METAR?

In degrees Celsius, separated by a slash; 'M' indicates minus. Example: 18/12 = temp 18C, dewpoint 12C; M06/M12 = -6C / -12C.

How is altimeter setting coded in a US METAR?

An 'A' followed by four digits = inches of mercury. Example: A2992 = 29.92 in Hg.

What do these common METAR weather codes mean: -RA, +TSRA, BR, FG, HZ?

-RA = light rain; +TSRA = heavy thunderstorm with rain; BR = mist; FG = fog; HZ = haze. (- light, no sign moderate, + heavy.)

What is a PIREP and why is it valuable?

Pilot Weather Report - actual conditions reported by pilots in flight. It is the only direct source of in-flight info on turbulence, icing, and cloud tops/bases.

What are the two types of PIREPs?

UA (routine) and UUA (urgent). Urgent reports cover hazards like severe/extreme turbulence, severe icing, hail, wind shear, tornadoes, or volcanic ash.

What is a TAF?

Terminal Aerodrome Forecast - a forecast of expected weather within ~5 statute miles of an airport, normally valid for 24 or 30 hours and issued 4 times daily.

What do FM, BECMG, and TEMPO mean in a TAF?

FM (from) = rapid/significant change at a stated time; BECMG (becoming) = gradual change over a period; TEMPO = temporary fluctuations lasting under 1 hour.

How does a TAF differ from a METAR in coding?

Both use similar formats, but a TAF is a forecast for a period (with valid time group) and does NOT include temperature/dewpoint in the standard body (except some max/min temp groups).

What is the Wind and Temperature Aloft Forecast (FB/FD)?

A forecast of wind direction, speed, and temperature at specified altitudes. Used for flight planning altitude selection and fuel estimates.

In a winds aloft forecast, how do you decode a group like 2420-04?

Wind from 240 deg true at 20 kt, temperature -4 degC. Direction is true north; below 24,000 ft temps may be + or -, above 24,000 always negative (sign omitted).

In a winds aloft forecast, what does a coded direction over 36 (e.g., 7330) indicate?

Wind speed of 100 kt or more: subtract 50 from the direction and add 100 to the speed. 7330 = 230 deg at 130 kt.

At what wind speed are winds aloft NOT forecast, and how is that shown?

When speed is light/variable (under 5 kt), it is coded '9900' meaning light and variable.

Why is there no wind/temp forecast for an altitude within 1,500 ft of the station elevation?

Surface effects make low-level forecasts unreliable; the lowest forecast level must be at least 1,500 ft above the station.

What is an AIRMET (WA)?

Airmen's Meteorological Information - advisory of weather hazardous to light/smaller aircraft, less severe than a SIGMET.

What are the three types of AIRMET?

Sierra (IFR conditions/mountain obscuration), Tango (turbulence/strong surface winds/wind shear), and Zulu (icing and freezing levels).

What is a SIGMET (WS)?

Significant Meteorological Information - advisory of weather hazardous to ALL aircraft: severe icing, severe/extreme turbulence, dust/sand storms, and volcanic ash.

What is a Convective SIGMET (WST)?

An advisory for convective (thunderstorm) activity: severe/embedded thunderstorms, lines of thunderstorms, and tornadoes/hail. Implies severe turbulence, icing, and wind shear.

How long is a Convective SIGMET valid?

Issued for up to 2 hours, updated hourly.

What is radar (NEXRAD / weather radar) used to detect?

Areas and intensity of precipitation. It detects precipitation, not clouds. Useful for locating thunderstorms and heavy precip.

What is the limitation of using onboard or datalink (NEXRAD) radar near thunderstorms?

Datalink radar imagery can be several minutes old (latency); never use it to penetrate or skirt close to storms - use it for strategic, not tactical, avoidance.

What does satellite imagery show, and what are the two main types?

Cloud cover and weather systems. Visible imagery shows cloud reflectivity (daytime only); infrared imagery shows cloud-top temperatures (day or night).

What is a Surface Analysis Chart?

A chart showing actual surface weather: pressure systems (highs/lows), fronts, isobars, and station data at a specific time.

What are isobars on a surface chart?

Lines connecting points of equal barometric pressure. Closely spaced isobars indicate strong pressure gradient and strong winds.

What is a Surface Prognostic (Prog) Chart?

A forecast chart showing expected positions of pressure systems, fronts, and areas of precipitation for a future time.

What are AWC Forecast Graphics?

Graphical forecast products from the Aviation Weather Center (aviationweather.gov), including the Graphical Forecasts for Aviation (GFA) - the modern replacement for textual area forecasts.

What are the main preflight weather sources for pilots today?

1800wxbrief.com (Leidos Flight Service), aviationweather.gov (Aviation Weather Center), EFB apps (ForeFlight, etc.), and DUATS replacements/approved vendors.

What is Flight Service (FSS) and how do you reach it for a briefing?

Flight Service provides preflight briefings, opens/closes flight plans, and gives in-flight services. Reach it by phone at 1-800-WX-BRIEF or online at 1800wxbrief.com.

What are the three types of weather briefings?

Standard, Abbreviated, and Outlook briefing.

When do you request a STANDARD briefing?

When you have not received prior information and want a complete picture for your flight. It is the most complete briefing.

When do you request an ABBREVIATED briefing?

To update a previous briefing or get specific/limited items only.

When do you request an OUTLOOK briefing?

When your proposed departure is 6 or more hours away - for general planning purposes.