Meteorology
What the exam tests
This domain tests weather interpretation for VFR flight: pressure and altimetry, stability, clouds, fronts, icing, thunderstorms, dust and the decoding of METAR and TAF reports.
Core rules
- Pressure decreases with height. QNH is the altimeter setting that gives elevation; QFE gives height above a datum; standard pressure 1013.2 hPa is used at flight levels.
- Stability controls cloud type. Unstable air gives cumulus, showers and turbulence; stable air gives stratiform cloud and steady precipitation.
- A cold front brings a narrow band of heavy showers, squalls and possible thunderstorms; a warm front brings extensive stratiform cloud and steady rain.
- Icing is most likely in supercooled cloud between 0°C and about -20°C. Carburettor icing can occur at higher temperatures.
- In Iran, summer heating over the interior produces convective turbulence and dust; winter radiation fog can form in basins and at aerodromes. Mountain areas such as the Alborz and Zagros produce lee turbulence and wave activity.
- METAR wind is true direction; ATIS and runway reports may use magnetic direction.
Worked example
Temperature 24°C and dew point 14°C give a spread of 10°C. Using about 400 ft per 1°C of spread, the convective cloud base is near 4,000 ft AGL. If the terrain rises to 3,500 ft, VFR clearance may be marginal and the route should be replanned.
Traps
Confusing QNH and QFE; reading visibility in metres as statute miles; treating TEMPO as a permanent change; and underestimating dust, haze or mountain wave.