Weather Flashcards
What is a trough?
Elongated area of relatively low atmospheric pressure. Associated with rising air, hence the general association of bad weather.
What are the general characteristics of air flow around low and high pressure systems?
Low=inward, upward, and counterclockwise
High=outward,downward, and clockwise
What is a ridge?
Elongated area of relatively high atmospheric pressure. Air is descending which results in the dissipation of cloudiness; hence the association of high pressure and good weather
What are the standard temperature and pressure values for sea level?
15*C and 29.92” Hg
What are “isobars”?
A line on a weather chart which connects areas of equal or constant barometric pressure
If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information does that provide?
Closely spaced isobars = steep pressure gradient = higher wind speeds
What causes the winds aloft to flow parallel to the isobars?
The Coriolis Force
Why do surface winds generally flow across the isobars?
Surface Friction
At what rate does atmospheric pressure decrease with an increase in altitude?
1” Hg per 1,000 feet
What does “Dew Point” mean?
The temperature at which a sample of air must be cooled to attain saturation
When temperature and dew point are close together (within 5*), what type of weather is likely?
Visible moisture in the form of clouds, dew, or fog. Also, these are IDEAL CONDITIONS FOR CARBURETOR ICING!!!
What factors primarily determine the type and vertical extent of clouds?
The stability of the atmosphere
How do you determine the stability of the atmosphere?
Unstable Air = temp decreases uniformly and rapidly as you climb (close to 3*c per 1000ft). If temp remains unchanged or slightly decreased, the air tends to be stable.
What are the signs of stable and unstable air seen in clouds, turbulence, precipitation, and visibility?
Stable Unstable
Clouds …………. Stratiform …………….. Cumuliform
Turbulence……… Smooth ………………….. Rough
Precipitation …… Steady ………………….. Showery
Visibility ……….. Fair to Poor ………………. Good
How can you determine what altitude above the surface you can expect cumuliform clouds based on temperature and dew point?
( (Temp-DewPoint) /4) x 1,000 = Base of clouds Ex: Temp 82*, DP 62* 1) 82-62=20 2) 20/4=5 3) 5*1000= 5,000 feet
What conditions are necessary for structural icing to ocur?
Visible moisture and below freezing temperatures at the point moisture strikes the aircraft
What are the main types of icing an aircraft encounters in flight?
Structural, induction system, and instrument icing.
Name the three types of structural icing that may occur in flight
Clear Ice, Rime Ice, and Mixed Ice
Describe Clear Ice
Liquid drop strikes the aircraft, flows out over the aircraft surface, and gradually freezes into a smooth sheet of solid ice
Describe Rime Ice
small drops (such as those in stratified clouds or light drizzle) strikes the aircraft and freezes rapidly before the drop can spread out over the aircraft’s surface.
Describe Mixed Ice
Different sized liquid drops are intermingled with snow or ice particles . The ice particles become imbedded in clear ice, building a very rough accumulation.
What should you do if you encounter icing conditions?
Change course and/or altitude.. usually climb to a higher altitude if possible.
What factors must be present for a thunderstorm to form?
1) A source of lift (heating, fast moving front)
2) Unstable air (nonstandard lapse rate)
3) High Moisture content (temperature/dew point are close)
Is frost considered a hazard to flight? Why?
Yes! It does not change the shape of the wing, however, it can spoil the smooth flow of air due to the roughness. The aircraft may not be able to takeoff at normal takeoff speeds
What are the 3 stages of a thunderstorm?
1) Cumulus - Updrafts cause raindrops to increase in size
2) Mature Stage - Rain and lightning at Earth’s surface. Rain usually falls besides or through the updrafts
3) Dissipating Stage - Downdrafts and rain begin to dissipate
What are the two basic ways that fog may form?
1) Cooling the air to the dew point
2) Adding moisture to the air near the ground
Name several types of Fog
1) Radiation Fog
2) Advection Fog
3) Upslope Fog
4) Precipitation-induced Fog
5) Ice Fog
What causes radiation fog to form?
The ground cools to the adjacent air to the dew point on calm, clear nights
What is advection fog, and where is it most likely to form?
Warm humid air is moved over a cold surface. Pilots will usually experience this along coastal areas during the winter. Unlike Radiation Fog, it may occur with winds, cloudy skies, over a wide geographic area, and at any time of the day or night.
What is Upslope Fog?
Fog that results from moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the slope wind ceases, the fog dissipates.
What is wind shear and where is it likely to occur?
Change in windspeed or direction. It can happen at any layer of the atmosphere, but the areas of special concern are:
1) Wind shear with a low level temperature inversion
2) Wind shear in a frontal zone or thunderstorm
3) Clear air turbulence (CAT) in the jet streams
What is the primary way of obtaining a weather briefing?
AFSS/FSS on the phone 1-800-WXBRIEF
What are some other ways to obtain weather briefings?
Telephone Information Briefing Service (TBS) (AFSS)
DUAT/DUATS
Other private sources such as WSI
What types of briefings are available from AFSS/FSS Briefer?
Standard Briefing - When you haven’t received a previous briefing
Abbreviated Briefing - When you only need 1 or 2 items - after you’ve already received a standard briefing
Outlook Briefing - When you’re proposed departure time is six or more hours in the future
What information is covered in a weather briefing?
Adverse Conditions VFR Flight Not Recommended Synopsis Current Conditions Enroute Forecasts Destination Forecast Winds aloft NOTAMS ATC Delays
What is EFAS?
En Route Flight Advisory Service - provide enroute aircraft with weather advisories and collects PIREPs. Valid for aircraft between 5,000’AGL and 17,500’MSL. It is on frequency 122.0 aka “Flight Watch”
What is HIWAS?
Hazardous In-Flight Weather Advisory Service - Continuous broadcast of in-flight weather advisories including Aviation Weather Warnings, SIGMETs, Convective SIGMETs, Center Weather Advisories, AIRMETs, and urgent PIREPs. Depicted on sectional charts with an “H” in the upper right corner of the Ident Box.
What is a METAR is what are the two types?
METAR - Hourly surface observation of the conditions observed. 2 types are routine and a SPECI which may be given at any time for rapidly changing weather conditions, aircraft mishaps, or other critical conditions.
What are Radar Weather Reports (SD)?
Contains information about precipitation observed by weather radar. Transmitted hourly. Should only be used if no other radar information is available
What is an aviation area forecast?
“FA” is a forecast covering flight information of a region. Pilots should used the FA in conjunction with AIRMETs and SIGMETs to determine enroute weather and interpolate conditions at an airport without TAFs. FAs are issued 3 times daily.
What information is provided by an “FA”?
Note: “FA”s cover the US and extend from the surface to FL450
a) Synopsis - discusses the synoptic weather affecting the FA during the 18 hour valid period
b) Clouds and Weather - description of the clouds and wx for the first 12 hours
c) 12 to 18 Hour categorical outlook - IFR, MVFR, or VFR, including expected precip and/or obstructions to visibility
What are In-Flight Aviation Weather Advisories (WST, WS, WA)?
Forecasts to advise en-route aircraft of development of potentially hazardous weather in 3 types: SIGMET, AIRMET, and Convective SIGMET. All heights are in MSL, except when you see “CIG” which indicated AGL
What is a Convective SIGMET?
- Valid for up to 2 hours
- Wings greater than 50 knots
- Hail at the surface greater than 3/4 in.
- Tornadoes
- Embedded T-Storms
- A line of T-Storms
- When precip affects 40% or more of an area at least 3,000 square miles
What is a SIGMET (WS)?
advises of NON-CONVECTIVE weather that is potentially hazardous to aircraft
- Severe Icing not associated with a T-Storm
- Severe or Extreme Turbulence or clear air turbulence (CAT) not associated with T-storms
- Dust storms or sandstorms lowering surface or inflight visibilities below 3 miles
- Volcanic Ash
What is an AIRMET (WA)?
3 types:
- AIRMET Sierra - “I cant ‘See’” - IFR or mtn obsc.
- AIRMET Tango - “Turbulence” - mod turbulence, sfc winds 30 knots +, and/or non-convective low level wind shear
- AIRMET Zulu - “freeZing” - Moderate icing and provides freezing level heights
Describe the Winds and Temps aloft forecasts (FB)
- Note: Winds are not issues within 1500AG: of a location’s elevation
- Note: Above FL240, the negative sign for temperature is omitted
- Note: Temperature is not given within 2,500 ft AGL of location’s elevation
- Note: Light and Variable winds less than 5 knots are written as 9900
- Note: Forecast winds 100-199 knots are indicated by subtracting 100 from the speed and adding 50 to the wind direction hdg
- Note: Winds 200 knots or greater are indicated as 199 knots
What are Center Weather Advisories (CWA)?
Warning to aircrews to anticipate and avoid adverse weather conditions in the en-route and terminal environments. Valid for 2 hours.
What is a Surface Analysis Chart?
- Transmitted every 3 hours
- locates pressure systems and fronts
- gives an overview of winds, temps, and dew point temps at time the chart was produced
What information does a Weather Depiction Chart provide?
computer generated chart based on METAR reports. Chart begins at 01z every day, and is transmitted ever 3 hrs.
What are Radar Summary Charts?
A graphical display of (SDs). Displays areas of precipitation including type, intensity, configuration, coverage, echo top, and cell movement.
What are constant pressure analysis charts?
Graphical display of areas of equal pressure. Issued twice daily at 00z and 12z.
Text Weather Products
METAR (SD) Once Per Hour TAF (TAF) 4x a day, 5SM radius Area Forecast (FA) 3x a day Covers 18 hours Winds Aloft (FD) 2x a day Referenced to TRUE North No wind within 1500agl, no temp within 2500agl Radar Weather Reports :35 past hour Doesn't show clouds, movement direction is FROM PIREPS (UA/UUA) Observations AIRMET (WA) Scheduled - 6 hours, unscheduled as necessary SIGMET (WS) Unscheduled, valid for 4 hours Severe Turbulence, Severe Icing, Volcanic Eruption, and Sandstorms Convective SIGMET (WST) Scheduled - hourly +55, valid for 2 hours Surface winds +50kts, hail +3/4in, and tornadoes
Weather Charts
Surface Analysis
Every 3 hours
Station models, fronts, isobars, and pressure systems
Weather Depiction
Every 3 hours
Uses metars. Contour lines = MVFR, shaded = IFR
Radar Summary
:35 past the hour
Doesn’t show VFR/MVFR/IFR, doesn’t show clouds
Sig. WX Prog Charts
4x a day
Left side = 12 hrs, Right side = 24 hrs
Upper = Sig WX (VFR/MVFR/IFR, freezing levels, turbulence)
Lower = Surface Wx (precip, fronts, and pressure)
