Weather Flashcards
Air Stability
Ability of atmosphere to resist vertical motion. Measured by the difference between the temperature lapse rate of a given parcel of air, compared to the dry adiabatic lapse rate (3c per 1000). Dry/cool air is more stable. Inversions also help.
Turbulence procedures
- slow to Va (or slower)
- maintain level flight, while accepting changes in airspeed or altitude
- exit the situation however practicable
Wind shear/microburst procedures
- detection: sudden unexplained changes in airspeed or VSI
- be prepared to respond to the opposite effect
- exit the area, make a report
Structural icing procedures
- react quickly. Even a sandpaper amount of ice can reduce lift by 30% and increase drag by 40%. And it can accumulate as much as 3 inches in 5 minutes.
- notify ATC (possibly with urgency) and get an amended clearance: different altitude (out of freezing level), or different route (out of precip)
- report the PIREP
- expect a significantly higher stall speed on landing
- never take off with frost on the plane
Jet stream speed
50kts or greater
Tropopause height
Ranges from 20,000 at the poles to 65,000 at the equator. Average is 37,000
Tropopause defined by
Sharp change in the temperature lapse rate
Standard temperature and lapse rate
15c at sea level. Decreases 2c per 1000ft
Air circulation direction (northern hemisphere)
High pressure: clockwise
Low pressure: counterclockwise
Causes of wind deflection
Near the ground (<2000agl): friction causes it to move toward the lower pressure. Contours also affect.
In the air: coriolis force deflects at a right angle (northern hemisphere)
Increased precipitation comes from
Upward currents. Cloud particles collide and merge faster, creating more precip and bigger drops
Ice pellets on the surface always indicates
Freezing rain at a higher level
Standing Lenticular clouds
Lens shaped clouds that form on the crests of air rotating near mountains. Indicator of strong turbulence
Cloud families
High, mid, low, and “clouds with extensive vertical development”
Fair weather cumulus clouds indicate
Bumpy turbulence beneath the cloud, but good visibility. The top of the cloud is the upper limit of convection, meaning smooth air above
Fog types
Radiation: cold ground cools the air to its dew point
Advection (sea) fog: moist air is blown over cooler land or water
Upslope: moist air is blown up a slope and cooled to its dew point
Thunderstorm ingredients
Moisture, Lift, and Unstable air
Thunderstorm stages
Cumulus: rising air. Continuous updrafts and lowering pressure
Mature: precipitation begins, as do downdrafts. High intensity.
Dissipating: mostly downdrafts
Squall lines - what, and where?
Narrow band of active thunderstorms. Winds of at least 16kts rising to 22kts for 1+ minute. Usually forms ahead of a cold front, but CAN develop in unstable air anywhere
Inadvertent Thunderstorm penetration procedures
- Keep your eyes on your instruments
- Maintain reduced airspeed
- Fly straight through
- Maintain attitude, but dont force altitude
Microburst duration & strength.
Rarely longer than 15 mins. However, there may be multiple microbursts in an area. Downdrafts as strong as 6000 fpm, horizontal winds as strong as 45kts each way (90 total shear)
Conditions for frost
Freezing air at the surface that is also below the dew point
Conditions that produce the highest levels of accumulation of structural icing
Large supercooled water droplets (AKA Freezing rain)
What is one good thing freezing rain indicates?
There must be a layer above of warmer air in order for supercooled droplets to form
Effect of snow or frost with the roughness of coarse sandpaper
Reduces lift by as much as 30% and drag by as much as 40%
Procedure: landing with ice build up
Land at a higher speed, with minimum large/abrupt configuration changes, and minimum flaps, to account for
- decreased thrust (from lift and drag) and
- the possibility of a tailplane/empennage stall (due to ice building up undetected on the horizontal stabilizer)
Procedure: encountering ice in flight
Leave the area of precipitation and/or change to a warmer OR much colder (-10c) altitude (either may be higher or lower), disable autopilot
Indicators of impending tailplane stall
Elevator control pulsing, oscillation/vibration, abnormal nose-down trim change, reduction in elevator effectiveness, sudden change in elevator force, uncommanded nose-down pitch
Procedure: suspected tailplane ice
Retract flaps, nose up, add power, operate de-icing equipment several times, and make nose-down pitch changes cautiously
Procedure: roll upset (due to icing)
Increase airspeed, extend flaps to first setting, operate de-icing systems
Risks of climbing out in icing conditions
Ice may develop on the underside and farther back than in cruise flight and therefore go undetected. Use of autopilot, especially VS mode highly discouraged
Icing: first place to form
Small protuberances and the tailplane
Typical wind shear location
LLWS: Strong temperature inversions, on all sides (up to 15 miles) or below a thunderstorm cell, near frontal activity
WS: any change in wind, esp up to 6 hours ahead of a warm front (<5000agl) , 3 hours behind a cold front >5000agl)
TAF Validity
5 mile radius of the center of an airport’s runway complex during a 24 hour period
PIREP (UA) Components
OV over location TM time FL altitude TP aircraft type SK sky cover WX weather and visibility TA temperature WV wind TB turbulence IC icing RM remarks
Winds/temperatures aloft format
DDffTT
Direction (2 digit DD)
Velocity (ff)
Temperature (TT)
Winds light and variable are coded 9900
Direction greater than 50 = subtract 50 and add 100 to wind
Direction above 50 and wind greater than 99 = “more than 200 knots”
For altitudes greater than 24000, temperatures are always negative, so the sign is omitted
Wind aloft reports and forecasts given in what units and relative to what direction?
Knots, True North
Winds and temperatures aloft are forcast starting at what altitude above a station?
Temp = 2500+ Wind = 1500+
In flight weather advisory types
AIRMET: conditions significant to single engine/light aircraft (surface winds of 30+, wide spread IFR conditions, mountain obscurement, etc)
SIGMET: conditions significant to all aircraft (eg severe icing, dust storms, volcanic ash)
Convective SIGMETS: Thunderstorms, tornadoes, LLWS
AWW: severe weather forecasts
CWA: Center weather advisories
AIRMET/SIGMET broadcast on HIWAS at H+15 and H+45 Convective SIGMETS (WST) broadcast at H+15, 30, 45, and 55)
Report type AC
Convective outlook. Describes prospects for general thunderstorm activity for following 24 hours. Can be Slight, Moderate, or High.
Shown on a constant pressure chart
Temperature, dewpoint, wind, height, and height changes (12 hours)
Significant Weather (SIGWX) charts
Presents weather information that may impact flight planning. Comes in low level (FL240 and below) and high level (FL250-FL630) forecasts.
Low level: turbulence, freezing levels. Issued 4x daily.
High level: turbulence, cumulonimbus clouds, tropopause height, jet streams
SIGWX Jet Stream Pennants
50kts
Jet stream seasonality
Weaker and farther north in the summer, stronger and further south in the winter
