aero 2010 notes unit 3

Aviation Weather Service Program

• The aviation weather service program is a joint effort of the National Oceanic and Atmospheric Administration (NOAA), the Federal Aviation Administration (FAA), the Department of Defense (DOD), and commerce aviation weather

National Oceanic and Atmospheric Administration (NOAA)

NOAA is an agency of the Department of Commerce (DOC)
NOAA conducts research and gathers data about the global oceans, atmosphere, space, and Sun, and applies this knowledge to science and service, which touches the lives of all Americans.

National Weather Service (NWS)

The NWS provides weather data, forecasts, and warnings for the United States.

NWS data and products form a national information database and infrastructure that can be used by other government agencies, the private sector, the public, and the global community.

Aviation Weather Center (AWC)

• The Aviation Weather Center (AWC) in Kansas City, MO, issues aviation weather forecasts in support of the National Airspace System (NAS) including Airmen's Meteorological Information (AIRMET), Significant Meteorological Information (SIGMET), Convective SIGMETs, and various icing, turbulence, and convective forecast products.

Aviation Weather Center (AWC)

The AWC's website provides the aviation community with textual, digital, and graphical forecasts, analyses, and observations of aviation-related weather variables.
Additionally, the website provides information for international flights through the World Area Forecast System (WAFS) Internet File Service (WIFS).

The FAA

The FAA (DOT) provides a safe, secure, and efficient airspace system for the promotion of U.S. Aerospace Safety.
The FAA is required by Title 49 of the United States Code of Regulation to produce and manage aviation weather reports and forecasts.
The following are things that the FAA provides for connected to weather services:

ATC

Although ATC's primary responsibility is to maintain safety and efficiency in the NAS, it can provide updates on weather for aircraft.
Because weather is the number one cause of delays in the NAS, it is a major concern and accuracy of reports is of utmost importance

Flight Service

The FAA delivers flight services to pilots in the CONUS, Alaska, Hawaii, and Puerto Rico.
Services are provided by phone at 1- 800-WX-BRIEF, on the internet through the Flight Service Pilot Web Portal.
Services include, but are not limited to preflight weather briefings, flight planning, and in-flight advisories.

Aviation Weather Information

According to § 91.103, each pilot in command (PIC) shall, before beginning a flight, become familiar with all available information concerning the flight, including weather reports and forecasts.
This section will explain weather products produce by the NWS.

The Weather Briefing:

Prior to every flight, pilots should gather all information vital to the nature of the flight. This includes a weather briefing obtained by the pilot using online weather resources, a dispatcher, or Flight Service.
Phone call or “self briefing"

Types of Weather Briefings:

Standard Briefing: A standard briefing provides a complete weather picture and is the most detailed of all briefings. Looks at adverse conditions, VFR Restrictions, Synopsis and more! It also looks at non-weather items like NOTAMs and ATC delays.
Abbreviated Briefing: a shortened version of the standard briefing typically used when needing to update or supplement a previous standard briefing.
Outlook Briefing: used (rarely) when a flight is scheduled to depart 6 hours or more from briefing. Provides initial forecast information and Is limited in scope.

Graphical Forecasts for Aviation (GFA) Tool

The Graphical Forecasts for Aviation (GFA) Tool is a set of web-based displays that provide the necessary aviation weather information to give users a complete picture of the weather that may impact flights in the contiguous states.

Flight Information Service - Broadcast (FIS-B)

Pilots can receive a regulatory compliant briefing through online weather resources that can be used in conjunction with the Flight Information Service-Broadcast (FIS-B) products.
This is also capable of giving weather in the aircraft when coupled with ADS-B In.

In-Flight Updates:

The previous were online briefing formats but when in the aircraft there are several options for current weather as well.

FIS-B
ASOS and AWOS
ATIS
Flight Service

Weather Radar

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.
Radar enhancements have enabled more precision in detecting and displaying precipitation.

Doppler Radar

The National Weather Service developed the "Doppler" Radar in 1988 and it has been a staple in weather prediction and precipitation identification
Doppler uses a radio waves to detect any reflective mass (precipitation, bugs, ground interference, etc) in the atmosphere.

Backscatter Energy

Doppler works by emitting and receiving reflected energy.
This is shown in intensity by the reflectivity scale (color coded).

Power Output

The Doppler has a peak power output of 750 kilowatts (kW). This allows for better detection of low reflectivity (small) targets in the atmosphere, such as clouds, dust, insects, etc.
Most aircraft radars have a peak power output of less than 50 kW. Therefore, smaller targets are difficult to detect with aircraft radar.

Wavelength

The wavelength is about 10 cm for weather radar (3 cm for aircraft radars).
This shorter wavelength struggles to see "through" precipitation because of attenuation.
Attenuation is the process that reduces the energy in the radar beam.

Range Attenuation

The further away from the antenna the radar beam gets, the weaker the energy in it is.
This would result in "weaker" cells detected by the lower energy beam and must be compensated

Ground Clutter:

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.
Ground clutter appears stationary when animating images and can mask precipitation located near the radar.

Ghost

A Ghost is a diffused echo in apparently clear air caused by a "cloud" of point targets, such as insects, or by refraction returns of the radar beam in truly clear air,
Can be caused by low reflectivity echoes (super refraction) around sunset.

Mountain Weather

Mountains and Wind:

Some mountain winds are slow moving and predictable in their flow patterns.
Some however can be very hazardous and catch you off guard. When operating around mountainous terrain, always use extreme caution and get specialized training

Gravity Waves:

Develop in Stable Atmosphere
Lifted air seeks to return to is equilibrium.
Momentum is conserved
Compression and expansion affect altitude
Dampen with each "wave."

Kelvin-Helmholtz (K-H) Waves

When windshear is strong, K-H Waves can form
These are also known as Gravity-Shear Waves
The shear is connected to varying temperature and wind speed in the atmosphere
Typically, part of a temperature inversion

K-H Waves

"Shear" is by definition a different direction or speed in a fluid
When enough moisture is in the atmosphere, clouds will form if the cooler air is at the dewpoint.
Although not always a "Mountain wave" these are more common in

these regions

CAT

Clear Air Turbulence is created when this wave forms without humidity/moisture and dewpoint proximity (lack of clouds).
This is what makes CAT so dangerous, because it can occur in a relatively stable (but shallow) atmosphere with wind shear.

Vertically Propagated Mountain Waves

Energy is transferred vertically when air crosses a mountain
Because of density decrease at altitude, the amplitude (affect) of the mountain increases at altitude.

Wave Breaking

With a wave of modest amplitude, an aircraft flying through this region would likely experience appreciable "wave action," with altitude and/or airspeed fluctuations, but little turbulence.
However, with sufficient amplitude, the wave breaks and localized updrafts and downdrafts occur. The consequences for a pilot flying through this region include airspeed and altitude deviations and the possible sudden onset of severe or extreme turbulence

Wave Jump

Waves being compressed and then released creates a "jump" which forms rotors (areas of extreme turbulence) on the leeward side of the mountain.

Trapped Lee Waves

A "trapped lee waves" refers to the wave energy being confined below a certain altitude,
The mechanism confining this energy is strong wind shear above ridge level.

Trapped lee waves are most likely to occur when the wind crosses a narrow mountain range, with a layer close to ridge level and upstream of the mountain that has strongly increasing wind speed with height and high stability, capped by a layer of strong flow and low stability

Cloud formation

The Trapped Lee Wave can produce Altocumulus Standing Lenticular (ACLS) clouds

Rotors

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

Tropical Weather

Introduction:

Technically, the Tropics lie between latitudes 23½° N and 23½° S. However, weather typical of this region sometimes extends as much as 45° from the Equator.
One may think of the Tropics as uniformly rainy, warm, and humid. The facts are, however, that the Tropics contain both the wettest and driest regions of the world.

Circulation Patterns:

Previously we discussed that trade winds converge in the vicinity of the Equator where air rises.
This convergence zone is referred to as the Intertropical Convergence Zone (ITCZ). Here the seasonal temperature differences between land and water areas generate rather large circulation patterns that overpower the trade wind circulation; these areas are monsoon regions.
Tropical weather discussed here includes the subtropical high-pressure belts, the trade wind belts, the ITCZ, and monsoon regions.

Understanding Global Patterns

The Equator coincides with a "global" low pressure system.
30° Latitudes coincides with a global High pressure belt
60° Latitude coincides with a Sub-polar Low.
The poles coincide with a weak High pressure system.

Subtropical High-Pressure Belts

Land surfaces at the latitudes of the high-pressure belts are generally warmer throughout the year than are water surfaces.
Thus, the high-pressure belts are broken into semipermanent high-pressure areas over oceans with troughs or lows over continents.

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.
Moisture is trapped under the inversion; fog and low stratus occur frequently. However, precipitation is rare, since the moist layer is shallow, and the air is stable. Heavily populated areas also add contaminants to the air which, when trapped under the inversion, add to the visibility problem.

Continental Weather

In winter, the subtropical high-pressure belts shift southward. Consider southern California as an example.
The area comes under the influence of mid-latitude circulation, which increases the frequency of rain.
Also, an occasional wintertime outbreak of polar air brings clear skies with excellent visibility.
The situation on eastern continental coasts is just the opposite. 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. Precipitation is generally sufficient to support considerable vegetation.
For example, in the United States, Atlantic coastal areas at the same latitude as southern California are far from arid in summer.

Flying with Continental Weather

Low ceiling and fog often prevent landing at a west coast destination, but a suitable alternate generally is available a few miles inland.
Alternate selection may be more critical for an east coast destination because of widespread instability and associated hazards.

Open Sea Weather

Under a subtropical high over the open sea, cloudiness is fairly rare.
The few clouds that do develop have tops from 3,000 to 6,000 ft, depending on height of the inversion.
Ceiling and visibility are generally sufficient for VFR flight.

Island Weather

An island under a subtropical high receives very little rainfall because of the persistent temperature inversion. Surface heating over some larger islands causes light convective showers.
Cloud tops are only slightly higher than those over open water. Temperatures are mild, showing small seasonal and diurnal changes, A good example is the pleasant, balmy climate of Bermuda.

Intercontinental Convergence Zone (ITCZ)

Converging winds in the ITCZ force air upward. The ITCZ appears as a band of clouds consisting of showers (with occasional thunderstorms) that encircles the globe near the Equator.
It is estimated that 40 percent of all tropical rainfall rates exceed 1" per hour. Greatest rainfall typically occurs during midday.

Monsoon:

Over Asia, the subtropical high pressure breaks down completely. Asia is covered by an intense high during the winter and a well-developed low during the summer.
The same occurs over Australia and central Africa, although the seasons are reversed in the Southern Hemisphere.

Monsoon

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.

Monsoons

During the summer, Asia experiences extremely wet weather because of the deep Low system.
During the winter, rain is very sparces due to the high pressure system.
These latitudes tend to have more of a "wet" and "dry" season rather than a cold and hot.

Transitory Systems:

Prevailing circulations are not the only consideration in analyzing weather. Just as important, are migrating tropical weather producers-the shear line, the Tropical Upper Tropospheric Trough (TUTT), tropical waves, areas of converging northeast and southeast trade winds along the ITCZ, and tropical cyclones.

Tropical Upper Tropospheric Trough (TUTTs)

Troughs above the surface, generally at or above 10,000 ft, move through the Tropics, especially along the poleward fringes.
TUTTs and lows aloft produce considerable amounts of rainfall in the Tropics, especially over land areas where mountains and surface heating lift air to saturation.
Low-pressure systems aloft contribute significantly to the 300+ in. of annual rainfall over the higher terrain of Maui and the big island of Hawaii. Other mountainous areas of the Tropics are also among the wettest spots on Earth.

Tropical Cyclones

• "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. Wind gusts in these storms may be as much as 50 percent higher than the average wind speeds.

Tropical Cyclones:

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.

Hurricane Formation

The prerequisites for tropical cyclone development are optimum sea surface temperature under low-level convergence and cyclonic wind shear (Shear line).
Favored breeding grounds are shear lines, TUTTs, tropical waves, and lines of convection in low latitudes moving from the continent to the tropical ocean.

Hurricane Movement:

Tropical cyclones in the Northern Hemisphere usually move in a direction between west and northwest while in low latitudes.
As these storms move toward the mid-latitudes, they come under the influence of the prevailing westerlies. At this time, the storms are under the influence of two wind systems: the trade winds at low levels and prevailing westerlies aloft.
Thus, a storm may move very erratically, and may even reverse course or circle.

Decaying Hurricane:

As the storm curves toward the north or east (Northern Hemisphere), it usually begins to lose its tropical characteristics and acquires characteristics of lows in middle latitudes.
Cooler air flowing into the storm gradually weakens it. If the storm tracks along a coastline or over the open sea, it gives up slowly, carrying its fury to areas far removed from the Tropics.
However, if the storm moves well inland, it loses its moisture source and weakens from starvation and increased surface friction, usually after leaving a trail of destruction and flooding

What did you call me!?

Hurricanes are named after the Saffir-Simpson Hurricane Wind Scale.
This scale uses wind speed and house damage as the determining factor of "Category?"

Fog

Fog is a visible aggregate of minute water droplets that are based at the Earth's surface, and it reduces horizontal visibility to less than 5/8 sm (1 km); unlike drizzle, it does not fall to the ground.
Fog differs from a cloud only in that its base must be at the Earth's surface, while clouds are above the surface.
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 seldom forms when the temperature-dewpoint spread is greater than 2 °C (4 °F).
Fog is named after its "formation mechanism."

Radiation Fog

Radiation fog is a common type of fog, produced over a land area when radiation cooling reduces the air temperature to or below its dewpoint.
Thus, radiation fog is generally a nighttime occurrence and often does not dissipate until after sunrise.

Advection Fog

Advection fog forms when moist air moves over a colder surface and the subsequent cooling of that air to below its dewpoint. It is most common along coastal areas, but often moves deep into continental areas.
At sea, it is called sea fog. Advection fog deepens as wind speed increases up to about 15 kt. Wind much stronger than 15 kt lifts the fog into a layer of low stratus or stratocumulus clouds.

Advection Fog:

The west coast of the United States is quite vulnerable to advection fog. This fog frequently forms offshore as a result of cold water and then is carried inland by the wind.
It can remain over the water for weeks, advancing over the land during night and retreating back over the water the next morning

Upslope Fog:

Upslope fog forms as a result of moist, stable air being adiabatically cooled to or below its dewpoint as it moves up sloping terrain.
Winds speeds of 5 to 15 kt are most favorable since stronger winds tend to lift the fog into a layer of low stratus clouds. Unlike radiation fog, it can form under cloudy skies.
Upslope fog is common along the eastern slopes of the Rocky Mountains, and somewhat less frequent east of the Appalachian Mountains. Upslope fog is often quite dense and extends to high altitudes.

Frontal Fog:

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. A fog formed in this manner is called frontal (or precipitation-induced) fog
The result is a continuous zone of condensed water droplets reaching from the ground up through the clouds.
Frontal fog can become quite dense and continue for an extended period of time. This fog may extend over large areas, completely suspending air operations.
It is most commonly associated with warm fronts but can occur with other fronts as well.

Steam Fog:

When very cold air moves across relatively warm water, enough moisture may evaporate from the water surface to produce saturation,
As the rising water vapor meets the cold air, it immediately recondenses and rises with the air that is being warmed from below.
Because the air is destabilized, fog appears as rising filaments or streamers that resemble steam.

Freezing Fog:

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. Some surfaces that these droplets may freeze on include tree branches, stairs and rails, sidewalks, roads, and vehicles.

Mist:

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),
Mist forms a thin grayish vell that covers the landscape. It is similar to fog, but does not obstruct visibility to the same extent.
Mist can be thought of as the transition between fog and haze.

Haze:

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. Haze produces a bluish color when viewed against a dark background and a yellowish veil when viewed against a light background.
Haze may be distinguished by this same effect from mist, which yields only a gray obscuration.

Haze

A haze layer has a definite ceiling above which in-flight (air-to-air) visibility is unrestricted.
At or below this level, the slant range (air-to-ground) visibility is poor. Visibility in haze varies greatly, depending on whether the pilot is facing into or away from the Sun.

Smoke

Smoke is a suspension in the air of small particles produced by combustion due to fires, industrial burning, or other sources.
It may transition to haze. Not only can smoke reduce visibility to zero, but many of its compounds are highly toxic and/or irritating.
The most dangerous is carbon monoxide, which can lead to carbon monoxide poisoning, sometimes with supporting effects of hydrogen cyanide and phosgene.
Fog evaporates, but haze and smoke must be dispersed by the movement of air. A thick layer of clouds above haze or smoke may block sunlight, preventing dissipation. Visibility will improve little, if any, during the day.

Precipitation

Precipitation is any of the forms of water particles, whether liquid or solid, that fall from the atmosphere and reach the ground.
Snow, rain, and drizzle are types of precipitation. Heavy snow may reduce visibility to zero, Rain seldom reduces surface visibility below 1 mile except in brief, heavy showers.

Blowing Snow:

Blowing snow is snow lifted from the surface of the Earth by the wind to a height of 6 ft or more above the ground, and blown about in such quantities that the reported horizontal visibility is reduced to less than 7 sm (11 km).
Light, dry powder snow is most prone to being blown by the wind. When strong winds keep the snow suspended up to 50 ft (15 m) or so, obscuring the sky, and reducing surface visibility to near zero, it is called a whiteout. Visibility improves rapidly when the wind subsides.

Dust Storm:

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.
Fine-grained soils are commonly found in dry lake beds (called playas), river flood plains, ocean sediments, and glacial deposits.

Sandstorm

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 due to the larger size of the grain of sand.

Haboob

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 ml and rise vertically to the base of the thunderstorm.

Volcanic Ash:

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.
Ash can cause physical harm to humans and aircraft.

Arctic Weather

The Artic technically is anything that lies within 66.5°N (or south - Antarctica) Latitude.
Much of the weather we discuss here however will be applicable to Alaska, Russia, and other northern regions with prolonged darkness in winter.

Temperature

Winters are milder at coastlines.
Summers are warm in the interiors.
Cold weather is obviously abundant.

The Auroras

An aurora is a colorful light show in the sky caused by the Sun.
Auroras happen when particles from the Sun interact with gases in our atmosphere, causing beautiful displays of light in the sky.
Auroras are often seen in areas near the North Pole or South Pole.

Thunderstorms

TS Cell Life

The cell transitions to the mature stage when precipitation reaches the surface.
Precipitation descends through the cloud and drags the adjacent air downward, creating a strong downdraft alongside the updraft. The arc-shaped leading edge of downdraft air resembles a miniature cold front and is called a gust front.
Cumulonimbus tops frequently penetrate into the lower stratosphere as an overshooting top, where strong winds aloft distort the cloud top into an anvil shape. Weather hazards reach peak intensity toward the end of the mature stage.

There are three type of TS:

Single Cell
Multi Cell
Super Cell

Single Cell TS

A single-cell or common (also called ordinary-cell) thunderstorm consists of only one cell.
This type of thunderstorm often develops on warm and humid summer days.
Easy to navigate around (except night/embedded).

Multi Cell TS

A multicell cluster thunderstorm consists of a cluster of cells at various stages of their life cycle.
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.

Supercell TS

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 especally dangerous weather for pilots who encounter them.
Updraft speeds may reach 9,000 fpm (100 kt). This allows hazards to be magnified to an even greater degree.
Nearly all supercells produce severe weather (e.g., large hail or damaging wind) and about 25 percent produce a tornado.
A supercell may persist for many hours (or longer). New cells will continue to form if the three necessary ingredients exist.

TS Movement

Advection is the component of storm motion due to individual cells moving with the average wind throughout the vertical depth of the cumulonimbus cloud.
Propagation is the component of storm motion due to old cell dissipation and the new cell development. Storm motion may deviate substantially from the motion of the individual cells, which comprise the storm

TS Hazards

All thunderstorms have conditions that are hazards to aviation. These hazards occur in numerous combinations.
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.

Lightening

Every thunderstorm produces lightning and thunder. 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.
Lightning can damage or disable an aircraft. It can puncture the skin of an aircraft, and it can damage communications and electronic navigational equipment.

Downburst (Microburst)

The downward moving column of air in a typical thunderstorm is large. Convective clouds, shower cells, and thunderstorm cells sometimes produce intense downdrafts called downbursts that create strong, often damaging winds and wind shear.
Downbursts can create hazardous conditions for pilots and have been responsible for many LLWS accidents. Smaller, shorter-lived downbursts are called microbursts.

Microbursts

A typical microburst has a horizontal diameter of less than 2.5 mi and a nominal depth of 1,000 ft.
The lifespan of a microburst is about 5 to 15 minutes, during which time it can produce downdrafts of up to 6,000 fpm; increasing headwind and headwind losses of 30 to 90 kt, seriously degrading performance.
It can also produce strong turbulence and hazardous wind direction changes.

Tornados

A tornado is a violently rotating column of air in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud.
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.
Meteorologists have estimated that wind in such a vortex can exceed 200 kt; pressure in the vortex is an extreme low.

Tornado generators

Tornadoes occur with both isolated and squall line thunderstorms. However, over 80 percent of all tornadoes in the United States are produced by supercell thunderstorms.
Multiple tornado occurrences associated with a particular large-scale weather system is termed a "tornado outbreak." On rare occasions, one supercell can produce multiple tornadoes over many hours.
In addition, families of tornadoes have also been observed as appendages of the main cloud extending several miles outward from the area of lightning and precipitation. Thus, any cloud connected to a severe thunderstorm may contain hidden vortices

Water Ingestion

Turbine engines have a limit on the amount of water they can ingest.
If the updraft velocity in the thunderstorm approaches or exceeds the velocity of the falling raindrops, very high concentrations of water may occur.
It is possible that these concentrations can be in excess of the quantity of water that turbine engines are designed to ingest.
Therefore, severe thunderstorms may contain areas of high water concentration, which could result in flameout and or structural failure of one or more engines.