Chapter 2 - Weather Flashcards
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, and counterclockwise
High Pressure - outward, downward, and clockwise
What is a “trough”?
is an elongated area of realtively low atmospheric pressure.
What is a “ridge”?
is an elongated area of relatively high atmospheric pressure.
What are standard temperature and pressure values at sea level?
15 degrees C, 29.92” Hg
What are “isobars”?
line on a weather chart which connects areas of equal or constant barometric pressure.
What does the separation of the isobars on a weather map mean?
When isobars are close together the change in pressure is steeper, likewise the further apart they are the shallower the change is.
What causes the winds aloft to flow parallel to the isobars?
the coriolis force
Why do surface winds generally flow across the isobars at an angle?
surface friction
At what rate does atmospheric pressure decrease with an increase in altitude?
1” Hg per 1,000 ft
What does “dew point” mean?
Dew point is the temperature to which a sample of air must be cooled to attain a state of saturation.
When temperature and dew point are close together (within 5 degrees), what type of weather is likely?
Visible moisture in the form of clouds, dew, or fog.
What factor primarily determines the type and vertical extent of clouds?
The stability of the atmosphere.
How do you determine the stability of the atmosphere?
Unstable air - temperature decreases uniformly and rapidly as you climb. Likely to be around moist warm air.
Stable air - temperature remains unchanged or decreases only slightly.
List 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
At what altitude above the surface would a pilot expect the bases of cumuliform clouds if the surface temp is 82 degrees and the dew point is 62 degrees?
temperature - dew point
------------------------------ x 1,000 = base
4
Ex:
82-62=20
20/4=5
5 x 1,000= 5,000 ft AGLWhat type of wx info should you be aware of with respect to icing?
a. Location of fronts - type, speed, direction
b. Cloud Layers - bases and tops, PIREP’s
c. Freezing level(s)
d. Air Temp and Pressure - low pressure temps at and around freezing are bad
What is “freezing level”?
A altitude at which the temperature reaches 0 degrees C.
How can a pilot determine the freezing level?
Current Icing Product, Forecast Icing Products, freezing level graphics.
What conditions are necessary for structural icing?
Visible moisture and below freezing temperatures at the point the moisture strikes the a/c.
Name the main types of icing an a/c may encounter in-flight?
Structural, induction systems, and instruments icing.
Name the three types of structural icing that may occur.
Clear Ice - forms after initial impact when the remaining liquid portions of the drop flows out over the a/c surface, gradually freezing as a smooth sheet of solid ice.
Rime Ice - forms when drops are small, such as those in stratified clouds or light drizzle. The liquid freezes before it can spread out.
Mixed Ice - Forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become imbedded in clear ice, building a very rough surface.
What action is recommended if you inadvertently encounter icing conditions?
Climb or descend to warmer air or dryer air.
Is frost considered to be hazardous to flight?
Yes, because frost does not change the aerodynamics of the wing but it creates air separation from the surface spoiling lift.
What factors must be present for a thunderstorm to form?
a. sufficient water vapor
b. unstable lapse rate
c. initial upward boost (lifting) to start the storm process in motion
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 the updrafts; lightning; perhaps roll clouds
Dissipating stage - Downdrafts and rain begin to dissipate
What is temperature inversion?
An increase in temperature with increase in height.
State two basic ways that fog may form.
a. Cooling air to the dew point.
b. Adding moisture to the air near the ground.
Name the types of fog.
a. Radiation Fog
b. Advection Fog
c. Upslope Fog
d. Precipitation-induced fog
e. Ice Fog
What causes radiation fog to form?
The ground cools the adjacent air to the dew point on calm, clear night.
What causes advection fog?
Results from the transport of warm humid air over a cold surface. Most likely to form over coastal areas during the winter.
What is upslope fog?
Forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the upslope wind ceases, the fog dissipates. Upslope for is often quite dense and extends to high altitudes.
What is “wind shear”?
rate of change of wind in direction or velocity per unit of distance.
Where is wind shear likely to occur?
low level temp inversion, frontal zone or thunderstorm, clear air turbulence associated with jet stream
What types of weather info will you examine to determine if wish shear might affect your flight?
Terminal forecasts (LLWS), METAR’s, SIGMET’s, conv SIGMETS, LLWAS, PIREP’s
What is the primary means of obtaining a weather briefing?
AFSS/FSS 1-800 WX BRIEF
What are some examples of other sources of weather info?
a. Telephone Info Briefing Service (TIBS)
b. weather adn aeronautical info available from numerous private industry sources
c. Direct Used Access Terminal System (DUATS)
d. In Alaska, Transcribed Weather Broadcast (TWEB)
Where can you find a listing of AFSS/FSS and weather info numbers?
Airport/Facility Directory, US govt. section of the local phone directory
What types of wx briefings are available from an AFSS/FSS briefer?
a. standard briefing
b. abbreviated briefing
c. outlook briefing
d. inflight briefing
What pertinent information should a weather briefing include?
a. adverse conditions
b. VFR flight not recommended
c. synopsis
d. current conditions
e. enroute forecast
f. destination forecast
g. winds aloft
h. notices to airmen (NOTAM’s)
i. ATC delay
j. Special use airspace
What is EFAS?
En Route Flight Advisory Service
available from 5,000 AGL to 17,500 MSL on 122.0 MHz. Known as “flight watch”
What is HIWAS?
Hazardous In-Flight Weather Advisory Service, included on sectional with H in the top right corner of the ident box.
What is a “flight information service” (FIS)?
Additional source of receiving aviation weather.
What is a METAR and what are the two types?
hourly surface observation of conditions observed at an airport.
METAR - normal observation
SPECI METAR - given at any time for rapidly changingweather.
Describe serveral types of weather observing programs available.
Manual Observations - report made from airport staffed with FAA or NWS personnel.
AWOS - Automated weather observation system
ASOS/AWSS - Automated Surface Observation System/Automated Weather Sensor System. 25 NM range max of 10,000 ft. AGL
What are PIREP’s?
Pilot reports: UA - routine, UUA - Urgent
What are Radar Weather Reports (SD)?
Contains information about precipitation observed by weather radar. Textual product derived from the WSR-88D NEXRAD radar without human interaction. Shows coverage, precipitation, intensity, location, maximum tops, cell movement, and remarks.
What are Terminal Aerodrome Forecasts (TAFs)?
a concise statement of the expected meteorological conditions significant to aviation for a specified time period within 5 SM of the center of the airport’s runway complex.
Define “aviation area forecast”?
FA, the is a forecast of specified weather phenomena covering a flight info region. Issued 3 times daily for all 6 regions of the contiguos 48 states.
What information is provided by an FA?
Surface to 48,000 ft MSL includes:
a. synopsis - 18 hour valid period
b. clouds and weather - 12 hour period, amount (SCT, BRK, OVC) with bases higher than 1,000 ft AGL and below FL180, precipitation, visibility between 2 and 6 SM, sustained surface wind 20 kts or greater
c. 12 to 18 hour categorical outlook
What are Inflight Aviation Weather Advisories (WST,WS, WA)?
en route advisories of potentially hazardous weather in 3 types: SIGMET, convective SIGMET, and AIRMET.
When are convective SIGMET’s issued?
Embedded TS A line of TS Tornados Surface winds >50 kts Hail > 3/4 inch in diameter T Storms creating heavy precipitation that affects 40% or more of an area at least 3,000 sq. miles
What is a SIGMET (WS)?
non convective weather that is potentially hazardous to all aircraft. Maximum forecast period is 4 hours.
a. severe icing
b. severe or extreme turbulence or clear turbulence not associated with TS.
c. Dust/Sand Storms lowering vis to 3 SM or less
d. Volcanic Ash
What is an AIRMET (WA)?
Advisories of significant weather phenomena that describes conditions at intensities lower than those which require the issuance of SIGMET’s. Text (WA), graphic (G-AIRMET). Issued on a 6 hours beginning at 0245z.
What are thedifferent types of AIRMET’s?
a. Sierra - describes IFR conditions and or mountain obscurations
b. Tango - moderate turb, surface winds > 30 kts. non-convective LLWS.
Describes the wind and temperature aloft forecast (FB).
Wind and temperature aloft forecasts are computer prepared forecasts of wind directions, speed, and temp for specified locations, altitudes, and times. Produced 4 times daily. Not forecasted below 1,500 ft.,
What valuable information can be determined from Winds and Temperatures Aloft Forecasts (FB)?
Most favorable altitude, areas of possibles icing, temperature inversions, turbulence.
What information does a weather depiction chart provide?
Weather depiction chart is computer-generated from METAR reports. Begins at 01Z each day transmitted in 3 hour intervals.
Define the terms: LIFR, IFR, MVFR and VFR.
LIFR - Low IFR, ceiling less that 500 ft and/or visibility less than 1 mile.
IFR - Ceiling 500 to less than 1,000 ft and/or visibility 1 to less than 3 miles.
MVFR - Marginal VFR, ceiling 1,000 ft to 3,000 ft and/or visibility 3 to 5 miles inclusive.
VFR - Ceiling greater than 3,000 ft. and visibility greater than 5 miles, includes sky clear.
