Meteorology
Meteorology tests the atmosphere, pressure systems, clouds, icing, thunderstorms, wind shear and the interpretation of METAR, TAF and significant weather charts.
Standard atmosphere and pressure
- ISA sea level: 15°C, 1013.25 hPa, lapse rate 1.98°C per 1,000 ft up to the tropopause near 36,090 ft.
- Pressure falls about 1 hPa per 30 ft near sea level; altimeter errors follow from wrong subscale settings.
- Low pressure brings converging air and often cloud/rain; high pressure brings subsidence and clearer weather.
Clouds, icing and thunderstorms
- Cumulonimbus contains severe turbulence, icing, hail, lightning and microburst wind shear; avoid by at least 20 nm.
- Airframe icing is most likely between 0°C and −20°C in visible moisture; freezing rain is especially dangerous.
- Wind shear on approach requires immediate go-around if encountered.
Worked example
At FL300 the ISA temperature is 15 − (1.98 × 30) ≈ −44°C. If the OAT is −55°C, the ISA deviation is about −11°C. That cold air reduces tropopause height and can affect jet performance and altimetry; it is not a standard-day condition.
Traps that cost marks
- Mixing QNH and QFE when reading pressure values.
- Assuming all cloud at 0°C contains ice; visible moisture and lift are also needed.
- Reading a TAF as current weather; TAF is a forecast, METAR is an observation.