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