Weather Information Flashcards
Why do surface winds generally flow across the isobars at an angle?
surface friction
What are isobars?
a line on a weather chart which connects areas of equal or constant barometric pressure
Standard temperature and pressure values for sea level
15ºc and 29.92”Hg
What is a Ridge?
- elongated area of relatively high atmospheric pressure
- air moving out of a high depletes the quantity of air
- descending air
- dissipation of cloudiness
- high pressure
- good weather
MVFR
Marginal Visual Flight Rules
ceiling: 1,000’ - 3,000’
visibility: 3-5 miles
General characteristics of weather near a warm front
- stratiform clouds
- drizzle
- low ceilings
- poor visibility
- variable winds
- rise in temperature
The boundary area formed when a warm air mass contacts and flows over a colder air mass
warm front
At what rate does atmospheric pressure decrease with an increase in altitude?
1”Hg per 1,000’
Define Dew Point
the temperature at which a sample of air must be cooled to attain the state of saturation
The density of the air has a direct effect on:
- lift produced by the wings
- power output of the engine
- propeller efficiency
- drag forces
What factors affect air density?
In what way?
Altitude - the higher the altitude, less density
Temperature - the warmer the air, less density
Humidity - more humid air, less density
When temperature and dew point are close together (within 5º) what type of weather is likely?
visible moisture in the form of clouds, dew, or fog
ideal conditions for carburetor icing
What factor primarily determines the type and vertical extent of clouds?
the stability of the atmosphere
Define WS
SIGMET
valid 4 hours or 6 hours (tropical cyclones and volcanic ash)
- severe icing not associated with thunderstorms
- sever or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms
- widespread dust storms or sandstorms lowering surface visabilities to below 3 miles
- volcanic ash
Effects of stable and unstable air on clouds
stable : stratiform
unstable: cumuliform
Effects of stable and unstable air on turbulence
Stable: smooth
Unstable: rough
Significant precipitation is occuring at the surcace. How thick can you expect the clouds to be?
precipitation usually requires clouds to be at least 4,000’ thick
the heavier the precipitation, the thicker the clouds
During your preflight planning, what type of meteorological information should you be aware of with respect to icing?
- location of fronts
- cloud layers
- freezing layers
- air temperature and pressure
What does GFA stand for?
Graphical Forcast for Aviation
What are the three stages of a thunderstorm?
Cumulus stage
- updrafts cause raindrops to increase in size
Mature stage
- rain at earth’s surface
- it falls through or immediately beside updrafts
- lightning
- possible roll clouds
Dissipating stage
- downdrafts and rain begins to dissipate
LIFR Minimums
Low Instrument Flight Rules
ceiling: less than 500’
visibility: less than 1 mile
Define CWA
center weather advisories
valid for 2 hours
VFR Minimums
Visual Flight Rules
ceiling: greater than 3,000’
visibility: greater than 5 miles
(sky clear included)
Define DUATS
Direct User Access Terminal System
for obtaining preflight briefings and inflight weather information
Define DUATS II
Lockheed Martin Flight Services
for obtaining preflight briefings and inflight weather information
Define TWEB
Transcribed Weather Broadcast
(used in Alaska)
What types of weather briefings are available from a FSS?
standard briefing
abbreviated briefing
outlook briefing (6 or more hours before departure)
inflight briefing
What information should a weather briefing include?
- adverce conditions
- VFR flight not recommended
- synopsis
- current conditions
- enroute forecast
- destination forecast
- winds aloft
- NOTAMs
- ATC delay
- others upon request
What does HIWAS stand for?
Hazardous In-flight Weather Advisory Service
Name several types of fog
radiation fog
advection fog
upslope fog
frontal fog (precipitation-induced)
steam fog
Define WA
AIRMET
valid for 6 hours
- extensive moutain obscuration
- turbulence
- strong surface winds
- icing
- freezing levels
Effects of stable and unstable air on visibility
stable: fair to poor
unstable: good
What causes Radiation Fog?
the ground cools the adjacent air to the dew point
(calm, clear nights)
General characteristics of weather near a cold front
- towering cumulus or cumulonimbus
- heavy rain
- lightning
- thunder and/or hail
- tornadoes
- poor visibility
- variable winds and gusting
- temperature drop
- dew point drop
- pressure drop
What is a Trough?
- elongated area of relatively low atmospheric pressure
- at the surface when air converges into a low, it cannot go outward against the pressure gradient, nor can it go downward into the ground, it must go upward
- area of rising air
- cloudiness and precipitation
- low pressure and bad weather
Characteristics of Advection Fog
- results from the transport of warm humid air over a cold surface
- forms primarily along coastal areas during the winter
- may occur with winds
- may occur with cloudy skies
- over a wide geographic area
- any time of the day or night
Two basic ways fog may form:
cooling air to the dew point
adding moisture to air near the ground
What factors must be present for a thunderstorm to form?
sufficient water vapor
an unstable lapse rate
an initial upward boost (to start the storm process)
Characteristics of Upslope Fog
- forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain
- once wind ceases, fog dissipates
- quite dense
- extends to high altitudes
Define Wind Shear
- the rate of change of wind velocity (direction and/or speed) per unit distance
- expressed as vertical or horizontal wind shear
- occurs at any level in the atmosphere
Name the main types of icing an aircraft may encounter in-flight.
structural
induction
instrument
What does ADS-B stand for?
Automatic Dependent Surveilance - Broadcast
Types of PIREPs:
UA - routine
UUA - urgent
Effects of stable and unstable air on precipitation.
stable: steady
unstable: showery
What does AWOS stand for?
Automated Weather Observing System
What does ASOS stand for?
Automated Surface Observing System
What does AWSS stand for?
Automated Weather Sensor System
What does FA stand for?
Aviation Area Forcast
Define WST
Convective SIGMET
valid 2 hours
- severe or greater turbulence
- severe icing
- low-level wind shear
- issued hourly at H+55 (special bulletins any time)
- Severe thunderstorm due to:
- surface winds >50kts
- hail >¾”
- tornadoes
- Embedded thunderstorms
- A line of thunderstorms
- Thunderstorms producing heavy precipitation that affects 40% or more of an area at least 3,000 square miles
Occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air
Cold Front
When the forces of two air masses are relatively equal, the boundary or front that separates them
stationary front
What does TIBS stand for?
Telephone Information Briefing Service
What does TAF stand for and what are the types?
Terminal Aerodrome Forcast
TAF: routine forcast
TAF AMD: amended forcast
TAF COR: corrected forcast
The types of inflight aviation weather advisories
SIGMET
Convective SIGMET
AIRMET
Center Weather Advisory
IFR Minimums
ceiling: 500’ - 1,000’
visibility: 1 - 3 miles
When isobars are relatively close together on a surface weather chart or a constant pressure chart:
steep pressure gradient exists
high wind speeds
Define the three types of structural icing that may occur in flight.
Clear Ice
Forms after initial impact when the remaining liquid portion of the drop flows over the aircraft surface, gradually freezing as a smooth sheet of solid ice
Rime Ice
Forms when drops are small (stratified clouds or light). The liquid portion remaining after initial impact freezes rapidly before the drop has time to spread out over aircraft surface
Mixed Ice
Forms when drops vary in size or when liquid drops are intermingles with snow or ice particles. The ice particles become imbeded in clear ice building a very rough accumulation.
Occurs when a fast-moving cold-front catches up with a slow-moving warm front.
Occluded Front
3 areas of special concern for wind shear:
- wind shear with a low-level temperature inversion
- wind shear in a frontal zone or thunderstorm
- clear air turbulence (CAT) at high levels (associated with a jet stream or strong circulation)
What does FIS-B stand for?
Flight Information Service - Broadcast
Types of AIRMETs:
Sierra
- describes IFR conditions and/or extensive mountian obscurations
Tango
- moderate turbulence
- sustained surface winds greater than 30kts
- nonconvective low-level wind shear
Zulu
- moderate icing
- freezing level hights
What does FB stand for?
winds and temperatures aloft forcasts
Examples of NWS weather charts you will use during preflight planning
S surface analysis chart
W weather depiction chart
S short-range surface prognostic chart
S significant weather prognostic chart
C convective outlook chart
C constant pressure analysis chart
What causes the winds aloft to flow parallel to the isobars?
The Coriolis Force
State the general characteristics in regard to the flow of air around high and low pressure systems in the northern hemisphere
low pressure: inward, upward, counterclockwise
high pressure: outward, downward, clockwise
