Ch 3 - Weather Flashcards
atmospheric stability
the resistance of the atmosphere to vertical motion
Front characteristics
change in temperature
continuous decrease in pressure followed by an increase as the front passes
shift in wind direction
Unstable air
cumuloform clouds
showery precipitation
rough air (turbulence)
good visibility
Stable air
stratiform clouds/fog
continuous precipitation
smooth air
fair to poor visibility in haze and smoke
Lapse rate
the rate at which temperature falls with an increase in altitude
Three conditions required to produce thunderstorms
sufficient water vapor
unstable lapse rate
initial lifting force (upward boost)
wind shear turbulence
a hazardous and invisible atmospheric phenomena that can occur within 20 NM of a thunderstorm
microbursts
small-scale intense downdrafts which, as they get near the ground, spread outward from the center in all directions
squall line
nonfrontal, narrow band of active thunderstorms that often develop ahead of a cold front
Effects of structural icing
decrease in lift
weight and stalling speed increase for fixed wing, propellers may stall on rotary wing
decrease in thrust
increase in drag
structural icing
occurs on an aircraft whenever supercooled condensed droplets of water make contact with any part of the aircraft that is also at a temperature below freezing
Radiation fog
(ground fog) formed when terrestrial radiation cools the ground, which in turn cools the air in contact with it. When the air is cooled to its dew point (or within a few degrees), fog will form. This fog will form most readily in warm, moist air over low, flatland areas on clear, calm (no wind) nights.
Advection fog
(sea fog) formed when warm, moist air moves (wind required) over colder ground or water (i.e., when an air mass moves inland from the coast in winter)
Upslope fog
formed when moist, stable air is cooled to its dew point as it moves up along a sloping terrain (wind required). Cooling will be at the dry adiabatic lapse rate of approximately 3 degrees C per 1000 ft.
Precipitation-induced (rain or drizzle) fog
most commonly associated with frontal activity and is formed by relatively warm drizzle or rain falling through cooler air. Evaporation from the precipitation saturates the cool air and fog forms. This fog is especially critical because it occurs in the proximity of precipitation and other possible hazards such as icing, turbulence, and thunderstorms.
Steam fog
forms in the winter when cold, dry air passes from land areas over comparatively warm ocean waters. Low-level turbulence can occur and icing can become hazardous in steam fog.
Flight performance decreases:
As:
atmospheric pressure decreases
altitude increases
temperature increases
humidity increases
METAR
Aviation routine weather reports- observation of current surface weather reported in a standard international format
TAF
Terminal aerodrome forecasts - established for 5 SM within an airport
ASOS
Automated surface observing system - primary surface weather observing system of the US
AWOS
Automated weather observing system - derived from an automated system
WST
Convective SIGMET (significant meteorological information) - issued for severe thunderstorms with surface winds greater than 50 knots, hail > 3/4” in diameter, or tornadoes.
