Aviation Meteorology Theory and Weather Interpretation (CAA NZ PPL)
CAA NZ PPL Meteorology tests whether you can turn a forecast and a subscale setting into a safe decision. Expect to decode METAR, TAF and the NZ Graphical Area Forecast, apply altimetry, and explain how New Zealand's mountains, coasts and prevailing westerlies shape wind, cloud and visibility. The exam rewards candidates who link a weather line to an operational consequence.
Reading the reports
A METAR body is fixed-order: wind, visibility, weather, cloud, temperature/dewpoint, QNH. Wind in METAR and TAF is degrees true; ATIS and tower wind is magnetic - a classic misread. Visibility 9999 means 10 km or more; NZ reports visibility in metres. Cloud amounts are FEW (1–2 oktas), SCT (3–4), BKN (5–7), OVC (8), with heights in feet AGL. A TREND (NOSIG, BECMG, TEMPO) applies shortly after the observation. TAFs add a validity period and change groups: FM is a rapid change, BECMG a gradual change, TEMPO temporary fluctuations, and PROB30/40 a probability.
Altimetry and temperature
Below the transition altitude (13,000 ft AMSL in NZ) set QNH; above it set 1013.2 hPa. One hectopascal is about 30 ft. Flying from high to low pressure with the subscale unchanged makes the altimeter over-read, so the aircraft is lower than indicated. Cold air has the same effect.
New Zealand weather
Prevailing westerlies bring fronts, then a cold southerly change. Strong northwesterly flow over the Southern Alps produces mountain waves, severe turbulence and the föhn nor'wester of Canterbury and Otago, with lee-side cloud and wind. Daytime heating over land builds convective cloud, showers and sometimes hail.
Worked example
Departure QNH 1008 hPa, destination QNH 996 hPa: 12 hPa × 30 ft = 360 ft. If 1008 stays set, the altimeter over-reads by 360 ft, so an indicated 5000 ft is about 4640 ft true. Reset to destination QNH before descending below the transition altitude.
Traps that cost marks
Confusing true and magnetic wind; quoting QFE when QNH is asked; treating 9999 as unlimited visibility; mixing up BECMG and TEMPO; ignoring TAF validity; assuming a forecast without cloud means clear skies.