2E WX - Aviation WX Hazards Flashcards
- What are the two major classifications of thunder-storms? (AC 00-6)
Air mass thunderstorms—Most often result from surface heating. They occur at random in unstable air and last for only an hour or two. They reach maximum intensity and frequency over land during middle and late afternoon. Off-shore they reach a maximum during late hours of darkness when land temperature is coolest and cool air flows off the land over the relatively warm water.
Steady-state thunderstorms—Usually form in lines, last for several hours, dump heavy rain and possibly hail, and produce strong gusty winds and possibly tornadoes. They are normally associated with weather systems. Fronts, converging winds, and troughs aloft force upward motion spawning these storms which often form into squall lines. They are intensified by afternoon heating.
- What procedures should be followed when avoiding turbulence around thunderstorms? (AIM 7-1-29)
Never regard any thunderstorm lightly even when radar observers report the echoes are of light intensity. Avoiding thunderstorms is the best policy, but these are some “do’s and don’ts”:
a. Don’t land or take off in the face of an approaching thunderstorm. A sudden gust front of low-level turbulence could cause loss of control.
b. Don’t attempt to fly under a thunderstorm even if you can see through to the other side. Turbulence and wind shear under the storm could be disastrous.
c. Don’t fly without airborne radar into a cloud mass containing scattered embedded thunderstorms. Scattered thunderstorms not embedded can usually be visually circumnavigated.
d. Don’t trust the visual appearance to be a reliable indicator of the turbulence inside a thunderstorm.
e. Do avoid, by at least 20 miles, any thunderstorms identified as severe or giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus cloud.
f. Do clear the top of a known or suspected severe thunderstorm by at least 1,000 feet altitude for each 10 knots of wind speed at the cloud top. (Note: This should exceed the altitude capability of most aircraft.)
g. Do circumnavigate the entire area if the area has 6/10 thunderstorm coverage.
h. Do remember that vivid and frequent lightning indicates the probability of a severe thunderstorm.
i. Do regard as extremely hazardous any thunderstorm with tops of 35,000 feet or higher whether the top is visually sighted or determined by radar.
- Can ATC provide inflight assistance in avoiding thunderstorms and severe weather? (AIM 7-1-14)
Yes, to the extent possible, controllers will issue pertinent information on weather or chaff areas and assist pilots in avoiding such areas when requested. Pilots should respond to a weather advisory by either acknowledging the advisory or by requesting an alternate course of action as appropriate.
However, the controller’s primary responsibility is to provide safe separation between aircraft. Additional services such as weather avoidance assistance can only be provided to the extent that it doesn’t interfere with their primary function. ATC radar limitations and frequency congestion may also limit the controller’s capability to assist.
- Give some examples of charts and reports useful in determining the potential for and location of thunderstorms along your route. (AC 00-45)
a. Convective Outlook (AC)—a narrative and graphical outlook of areas of slight, moderate, or high risk of severe thunderstorms for a 24-hour period.
b. Significant Weather Chart (SIGWX)—provides a forecast of aviation weather hazards; depicts a snapshot of weather expected at the specified valid time.
c. Radar Summary Chart—graphically displays a collection of radar summary charts; depicts possible precipitation types, cell movements, maximum tops, locations of line echoes, and remarks.
d. Convective SIGMETs (WST)—issued for any convective situation involving severe, embedded, and lines of thunderstorms.
e. Pilot Reports (PIREPs)—help determine actual conditions along your planned route of flight.
f. Supplementary weather products—can be used for enhanced situational awareness; supplementary weather products must only be used in conjunction with one or more NWS primary weather products.
- What are microbursts? (AIM 7-1-26)
Microbursts are small-scale intense downdrafts which, on reaching the surface, spread outward in all directions from the downdraft center. This causes the presence of both vertical and horizontal wind shears that can be extremely hazardous to all types and categories of aircraft, especially at low altitudes. Due to their small size, short life span, and the fact that they can occur over areas without surface precipitation, microbursts are not easily detectable using conventional weather radar or wind shear alert systems.
- Where are microbursts most likely to occur? (AIM 7-1-26)
Microbursts can be found almost anywhere there is convective activity. They may be embedded in heavy rain associated with a thunderstorm or in light rain in benign-appearing virga. When there is little or no precipitation at the surface “accompanying the microburst, a ring of blowing dust may be the only visual clue of its existence.
- What are some basic characteristics of a microburst? (AIM 7-1-26)
Size: less than 1 mile in diameter as it descends from the cloud base; can extend 21⁄2 miles in diameter near ground level.
Intensity: downdrafts as strong as 6,000 feet per minute; horizontal winds near the surface can be as strong as 45 knots resulting in a 90-knot wind shear (headwind to tailwind change for traversing aircraft).
Duration: an individual microburst will seldom last longer than 15 minutes from the time it strikes the ground until dissipation. Sometimes microbursts are concentrated into a line structure, and under these conditions activity may continue for as long as an hour.
- Why is wind shear an operational concern to pilots? (AC 00-6)
Wind shear is an operational concern because unexpected changes in wind speed and direction can be potentially very hazardous to aircraft operations at low altitudes on approach to and departing from airports.
- What airplane characteristics will be observed in the following wind shear situations?
—a sudden increase in headwind.
—a sudden decrease in headwind.
Increased headwind—As a tailwind shears to a constant headwind, an increase in airspeed and altitude occurs along with a nose-up pitching tendency. The usual reaction is to reduce both power and pitch. This reaction can be dangerous if the aircraft suddenly encounters a downdraft and tailwind. Now the situation demands the exact opposite of the pilot’s initial reaction: a need for more performance from the airplane instead of less (more power/increased pitch attitude).
Decreased headwind—As a headwind shears to a calm or tailwind, pitch attitude decreases, airspeed decreases, and a loss of altitude occurs. The required action is more power and higher pitch attitude to continue a climb or remain on the glide slope.
- Concerning wind shear detection, what does the abbreviation LLWAS indicate? (AIM 4-3-7)
Low-Level Wind Shear Alert System (LLWAS) is a computerized system that detects the presence of a possible hazardous low-level wind shear by continuously comparing the winds measured by sensors installed around the periphery of an airport with the wind measured at the center of the airport. If the difference between the center field wind sensor and a peripheral wind sensor becomes excessive, a thunderstorm or thunderstorm gust front wind shear is possible.
- What types of weather information will you examine to determine if microburst/windshear conditions might affect your flight? (AC 00-54)
The following should be examined for clues of potential microburst/windshear conditions affecting the flight:
TAFs—examine the terminal forecast for convective activity.
METARs—inspect for windshear clues (thunderstorms, rainshowers, blowing dust).
Severe weather watch reports—check for issuance since severe convective weather is a prime source for microbursts and windshear.
LLWAS reports—Low Level Windshear Alert System, designed to detect wind shifts between outlying stations and a reference station.
SIGMETs and convective SIGMETs—may provide essential clues.
Visual clues from the cockpit—heavy rain (in a dry or moist environment) which can be accompanied by curling outflow, a ring of blowing dust or localized dust in general, flying debris, virga, a rain core with rain diverging away horizontally from the rain core, or tornadic features (funnel clouds, tornadoes). At night, lightning may be the only visual clue.
PIREPs—reports of sudden airspeed changes in the airport approach or landing corridors provide indication of the presence of windshear.
Airborne weather radar—to detect convective cells.
- Define wind shear and state the areas in which it is likely to occur. (AC 00-54)
Wind shear is the rate of change of wind velocity (direction and/or speed) per unit distance; conventionally expressed as vertical or horizontal wind shear. It may occur at any level in the atmosphere but three areas are of special concern:
a. Wind shear with a low-level temperature inversion;
b. Wind shear in a frontal zone or thunderstorm; and
c. Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.
