Meteorology
Meteorology
Meteorology tests your ability to read weather products and understand why conditions form: pressure systems, stability, humidity, fronts, icing, thunderstorms, wind shear and altimetry. You must decode METARs and TAFs and apply them to a go/no-go decision.
Core rules
- Pressure: altimeter setting is QNH, the pressure reduced to sea level. A3012 means 30.12 inHg; Q1013 means 1013 hPa. High pressure generally brings subsidence and fair weather; low pressure brings lift and cloud.
- Stability: unstable air favours cumuliform cloud, showers and turbulence; stable air favours stratiform cloud and smooth conditions.
- Icing: structural icing is most likely in freezing rain, in cloud at temperatures near 0°C, and in cumuliform cloud. Freezing rain is a severe hazard.
- Thunderstorms: avoid by at least 20 NM; expect gust fronts, hail, lightning and wind shear.
- Altimetry: flying from high to low pressure or warm to cold air, the altimeter over-reads unless you reset it.
Worked example
METAR CYVR 121200Z 09008KT 15SM FEW020 SCT040 12/09 A3012. Decode: Vancouver, 12th at 1200Z; wind 090° true at 8 kt; visibility 15 SM; few cloud at 2,000 ft, scattered at 4,000 ft; temperature 12°C, dew point 9°C; altimeter 30.12 inHg. The spread is 3°C, so the air is fairly moist but not saturated; VFR conditions are good.
Traps that cost marks
Treating A3012 as hPa, ignoring temperature error on the altimeter, and underestimating freezing rain are common. A distant thunderstorm still produces a gust front.