Weather Flashcards
Rotation of a high pressure system
Outward and clockwise (anti cyclonic)
Generally dry, stable, descending air.
Typically associated with good weather.
Coriolis force
Force created by the rotation of the earth which effects circulation patterns causing them to follow a curved path.
Low pressure
Inward, upward and counter clockwise (cyclonic)
Generally associated with bad weather.
Low level wind shear
Sudden and dramatic change in wind speed and/or direction over a small area. Extremely hazardous to aircraft. Directional changes of 180 degrees and wind speeds of 50 knots or more.
Types of fog
Radiation fog Advection fog Upslope fog Precipitation induced fog Ice fog
What are the three stages of a thunderstorm?
Cumulus stage: up drafts cause raindrops to increase in size.
Mature stage: rain at earth’s surface which falls through or immediately beside the updrafts, lightning and roll clouds.
Dissipating stage: down drafts and rain begin to dissipate.
Two basic ways fog can form
Cooling air to the dew point
Adding moisture to the air close to the ground
What is a temperature inversion?
An increase in temperature with height. A ground based inversion favors poor visibility. The air is stable with little or no turbulence.
What conditions are necessary for structural icing to occur?
Visible moisture and below freezing temperatures at the point moisture strikes the aircraft.
Types of icing that an aircraft may encounter in flight
Structural, induction system and instrument icing.
Recommended action for inadvertent encounter with icing conditions
Leave the area of visible moisture. Descend below the cloud base, climb above the cloud tops or turn to a different heading.
Factors necessary for the formation of a thunderstorm
Sufficient water vapor
An unstable lapse rate
An initial upward boost to start the storm process in motion
Rate of decrease in atmospheric pressure with increase in altitude
1” Hg per 1,000 feet above sea level
What are the effects of stable and unstable air on clouds, turbulence, precipitation and visibility?
Stable. - unstable Clouds: Stratiform - cumuliform Turbulence: smooth - rough Precipitation: steady - showery Visibility: fair to poor - good
What information should a weather briefing include?
Adverse conditions VFR flight not recommended Synopsis Current conditions Enroute forecast Destination forecast Winds aloft Notices to airmen
Define: EFAS
En route flight advisory is a service which provides en route aircraft with timely and meaningful weather advisories pertinent to the flight. On frequency 122.0 MHz. “Flight Watch”
Define: HIWAS
Hazardous in-flight weather advisory service is a continuous broadcast of in-flight weather advisories including summarized aviation weather warnings, SIGMETS, convective SIGMETS, AIRMETS, and urgent PIREPS.
Define: METAR
Hourly surface observations of weather conditions at an airport. A routine METAR is transmitted every hour while a SPECI can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps or other critical information.
Define: AWOS
Automated weather observation system; consists of sensors, a processor, a computer generated voice system and a transmitter to broadcast local minute by minute weather data to pilots.
Define: ASOS/AWSS
Automated weather observing system/automated weather sensor system; the primary U.S. Weather observing systems. Provide continuous minute by minute observations that generate METARs and other aviation weather information. Transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID.
Define: TAF
Terminal aerodrome forecast is a concise statement of the expected meteorological conditions significant to aviation for a specified time period within five statute miles of the center of the airport’s runway complex (terminal). Same codes as METAR
Define: FA
Aviation area forecast specifies weather phenomena covering a flight information region or other area designated by the meteorological authority. Issued three times daily for each of the six areas in the contiguous 48 states. Information provided:
Synopsis, clouds and weather, 12 to 18 hour outlook: IFR, MVFR, or VFR including precipitation and/or Obstructions to visibility.
LIFR
IFR
MVFR
VFR
LIFR: ceilings < 500' AGL
visibility < 1nm
IFR: ceilings 500'-1,000' AGL
visibility 1-3nm
MVFR: ceilings 1,000'-3,000' AGL
visibility 3-5nm
VFR: ceilings > 3,000'
visibility > 5nmSIGMET
Severe icing and/or turbulence not associated with a thunderstorm, dust or sandstorm lowering visibility less than 3nm, volcanic ash
Convective SIGMET
Severe thunderstorm with surface winds greater than 50 knots hail larger than 3/4” tornadoes, embedded thunderstorms, a line of thunderstorms or thunderstorms covering more than 40% of an area 3,000 square miles.
