Weather Flashcards
Every physical process of weather is the result of —-
Heat exchange
What causes differences in pressure and altimeter settings?
Unequal heating of the earths surface
What is the Coriolis force?
Deflects winds to the right in the Northern Hemisphere
Wind at 5000 agl is southwest while surface wind is south. This difference in direction is primarily due to—
Friction between the wind and the surface
( the Coriolis force at the surface is weaker than at higher altitudes)
A front is a —— separating …
Boundary
High pressure from low pressure
(The 2 air masses have different density)
There is always a ——- when flying across a front, but the most recognizable change is —-
Change in wind direction
Change in temperature
3 stages of a thunderstorm:
Cumulus -building
Mature- the beginning of rain
Dissipating- rains itself out
The greatest intensity of up/down drafts during a thunderstorm is
During the mature stage.
(The falling rain or hail creates strong downdrafts that spread out along the surface as cool gusty air)
Thunderstorms are produced by —- clouds
Cumulonimbus clouds
Under the anvil of a thunderstorm is usually …
Extreme Clear air turbulence
and hail
What is a squall line?
Non frontal
Band of thunderstorms
Ahead of a cold front
A thunderstorm by definition has —-
Lightening
What is structural icing
Ice that quickly coats the airplane surface
2 conditions required for structural icing:
1- visible moisture
2- temp at or below freezing
What causes the greatest accumulation of structural icing?
Freezing rain
(Freezing rain is super cooled water droplet that has not yet frozen. It freezes when in contact with a surface (wing) temp of 0c or below)
As freezing rain droplets at high altitudes begin to freeze,
they fall as what?
They fall as ice pellets
What kind of clouds are usually found on the leeward side of mountains?
Lenticular
2 aspects about Lenticular clouds …
They appear stationary
May contain wind 50 kts or more
Wind blowing ACROSS a mountain ridge usually produce
Mountain wave turbulence
3 times to expect wind sheer:
1- low level temp inversion
2- along frontal zones
3- clear air turbulence
When temp/dew point are within 5 degrees F, expect
Fog
Define dew point
The temp at which the air has 100% humidity
What determines how much water vapor can be held by the air?
Temperature
When does frost occur?
When the collecting surface temp is at or below dew point and dew point is below freezing
The direct conversion of water vapor to ice crystals (frost) is referred to as
Deposition
Water vapor becomes fog, clouds, or dew when
The water condenses
What is evaporation?
Process of converting liquid to vapor
What is sublimation?
Process of directly converting solid (like dry ice) to vapor
2 processes that add moisture to the air
Evaporation
Sublimation
What type of fog might occur during periods of clear sky, no wind, small temp/dew point spread
Radiation fog
What type of fog might occur as warm moist air moves over colder surface?
Advection fog
Warm moving over cold =
Advection
Cold air moving over warm water might produce what kind of fog?
Steam Fog
Warm rain falling through colder air produces what kind of fog?
Precipitation fog
Upsloping fog is produced when
Warm moist air is cooled as it is pushed up sloping terrain
The greatest turbulence is in —- clouds
Cumulonimbus
Stable air characteristics
Straight layered clouds
Smooth air
Poor visibility
Continuous rain
Cool/dry air
Unstable air characteristics
Vertical clouds (Cumuliform)
Rough air
Good vis
Scattered showers
Warm/humid air
Turbulence and clouds with extensive vertical development result when…
Unstable air rises
As a warm front approaches, (i.e. warm air cooled from cooler air below ) weather prior to frontal passage results in…
Stable air
Stratified (straight) clouds
No turbulence
What type weather conditions usually found beneath low-level temp inversion
Smooth air
Poor visibility
3 types of FSS weather briefings:
1- outlook- 6 hrs or more before flight
2- standard- before
3- abbreviated- to update a previous briefing
METAR- provide weather for what area?
Airfield and 5 mi radius
METAR- when issued
about 55 min past every hour
Wind reports are given in which: (true, magnetic,)
True
AWOS (automated weather observing system) updated when?
Once per minute
ASOS (automated surface observing system) is updated how often?
Hourly and is monitored by ATC
TAF (terminal airport forecast) is a forecast for what area?
Airport and 5 mi radius
How often is a TAF issued?
Every 6 hours (00z, 06z, 12z, 18z)
Inflight weather can be obtained on what frequency?
122.2
In a wind aloft forecast, if the wind speed is coded “9900” that means….
Winds are light and variable
In a winds aloft forecast, if the wind speed is over 100 kts, how does one decode? Example: “730649”
Subtract 50 from the first two #’s. to get direction
Add 100 to the next 2 #’s to get speed.
The last 2 #’s tell temp. Ever temp above 24,000 is negative.
In the example, (73-50) = 230*
(100 + 06 = 106 kts
SIGMET’S are for
All aircraft to inform of
CAT and/or
severe icing
not associated with thunderstorms
CONVECTIVE SIGMET’S include
Thunderstorm, embedded thunderstorms, Hail
For aviation purposes, a ceiling refers to …
The lowest BROKEN layer of clouds
Radar weather reports are of special interest to pilots because they indicate…
Location of precipitation and type,
Intensity ,
And cell movement of precip
Significant Weather Prognostic charts are best used for…
Determining areas to avoid ( freezing levels and turbulence)
What weather conditions define MVFR?
Ceiling: between 1-3 thousand
Vis: between 3-5 statute mi
What weather conditions define VFR
Ceiling > 3,000 agl
Vis > 5 statute mi
METAR and TAF reports cloud ceilings as (agl or msl)?
AGL
