Weather Flashcards
Standard Temperature for sea level.
59 degrees F/ 15 degrees C.
Standard pressure at sea level.
29.92 inches of mercury/ 1013.2 millibars.
Variations in altimeter settings
caused by unequal heating of the Earth’s surface.
Differences in direction between winds aloft and on the ground
caused by friction between the wind and the surface.
Every physical process of weather is accompanied by, or is the result of, a
heat exchange.
The boundary between two different air masses is referred to as a
front.
One of the most easily recognized discontinuities across a front is
a change in temperature.
One weather phenomenon which will always occur when flying across a front is a change in the
wind direction.
Clouds are divided into four families according to
height and range.
Nimbus
Rain cloud.
The colder the air is the less
vapor a cloud can hold.
Moisture is added to air by
evaporation (water to vapor) and sublimation (frost to vapor)
Dewpoint
Temperature to which air must be cooled to become saturated.
The amount of water vapor which air can hold depends on the
air temperature.
Clouds, fog, or dew will always form when
water vapor condenses.
What is the approximate base of the cumulus clouds if the surface air temperature is 70 degrees F and the dewpoint is 48 degrees F
70-48= 22
22/4.4=5
5x1000= 5000 FT AGL
If the temperature/dewpoint spread is small and decreasing, and the temperature is 62 degrees F, what type of weather is most likely to develop?
Fog or low clouds.
Airport elevation: 500 MSL Temp: 23 degrees C Dewpoint: 15 degrees C lapse rate: 2 degrees C Find the approximate base of the cumulus clouds.
4500 feet MSL
What clouds will you find in stable air?
- Stratiform clouds. (Flat type clouds)
- Steady precipitation
- Smooth air
- Poor surface visibility
Warming from below would decrease
the stability of an air mass.
Development of thermals depend upon
solar heating.
Unstable air
- Turbulence
- Good surface visibility
Moist, unstable airmass forms what type of clouds?
Cumuliform clouds and showery precipitation.
Towering cumulus clouds indicate
convective turbulence.
What measurement can be used to determine the stability of the atmosphere?
Actual lapse rate.
When warm, moist, stable air flows upslope, it
produces stratus type clouds.
If an unstable air mass is forced upward, what type of clouds can be expected?
Clouds with considerable vertical development and associated turbulence.
Steady precipitation preceding a front is an indication of
stratiform clouds with little or no turbulence.
Structural icing can only occur when in
visible moisture.
Highest accumulation rate of structural ice is in
freezing rain.
Ice pellets at the surface means
freezing rain at a higher altitude.
Frost forms when
temperature of collecting surface is at or below dewpoint of the air and the dewpoint has to be below freezing.
Temperature inversion occurs
when the air above is warmer than the air below.
Inversion layer with high relative humidity
- Smooth air
- Poor visibility, and fog, haze, or low clouds.
Wind shear zone in an inversion
windspeed is at 2000-4000 FT AGL and is at least 25 knots.
Radiation fog (ground fog) forms
in warm moist air over low, flatland areas on clear, calm nights.
Advection fog forms
when an air mass moves inland from the coast in winter.
Upslope fog
air cooling as it is forced to rise up a slope.
Two types of fog that depend on wind
- Advection fog
- Upslope fog
Steam fog
Low level turbulence/icing
Cumulonimbus (thunderstorm) clouds cause
greatest turbulence.
Thunderstorms must have
lightning.
Most dangerous type of thunderstorm
squall line.
Squall line
Non-frontal, narrow band of active thunderstorms.
To form cumulonimbus clouds you need
Lifting force, unstable air, and moist air.
What conditions are necessary for the formation of thunderstorms?
High humidity, lifting force, and unstable conditions.
During the life cycle of a thunderstorm, which stage is characterized predominately by downdrafts?
Dissipating.
The destination airport has one runway, “08-26” and the wind is calm. The normal approach in calm wind is a left hand pattern to runway 08. There is no other traffic at the airport. A thunderstorm about 6 miles west is beginning its mature stage, and rain is starting to reach the ground. the pilot decides to
fly an approach to runway 26 since any unexpected wind due to the storm will be westerly.
Inflight aviation weather advisories
AIRMETs SIGMETs and CONVECTIVE SIGMETs
AIRMETs
Warnings of weather conditions hazardous to small single-engine aircraft
Intended for all pilots.
SIGMETs
Warnings of weather conditions hazardous to all aircraft.
To determine the freezing level and areas of probable icing aloft, the pilot should refer to the
Inflight Aviation Weather Advisories.
What is indicated when a current Convective SIGMENT forecasts thunderstorms?
Thunderstorms obscured by massive cloud layers.
What information is contained in a Convective SIGMET?
Tornadoes, embedded thunderstorms, and hail 3/4 inch or greater in diameter.
Which in-flight advisory would contain information on severe icing not associated with thunderstorms?
SIGMET.
Wind shear can occur
at any altitude and all directions.
Where can wind shear be found
Low-level temperature inversion, frontal zones, and clear air turbulence.
Standing lenticular cloud
Stationary, almond or lens-shaped cloud that indicates the crest of a standing wave.
Winds of 40 knots or more.
When may hazardous wind shear be expected?
In areas of low-level temperature inversion, frontal zones, and clear air turbulence.
For aviation purposes, ceiling is defined as the height above the Earth’s surface of the
lowest broken or overcast layer or vertical visibility into an obscuration.
TAF
Terminal Aerodrome Forecast
GFA Graphical Forecasts for Aviation are weather charts best used to
learn the forecast weather along your proposed route of flight as well as at your destination if it has no terminal forecast.
