Meteorology
Meteorology tests the atmosphere, pressure, wind, clouds, fronts, icing, thunderstorms, fog, and the weather patterns that affect Japan. You must read METAR and TAF and apply local knowledge: winter monsoon, the Baiu rainy season, typhoons, and mountain effects.
Core concepts
- ISA: sea level 15°C and 1013.25 hPa; temperature falls about 2°C per 1,000 ft.
- Pressure and wind: air flows from high to low pressure; Coriolis turns it, and surface friction backs the wind.
- Stability: unstable air produces cumuliform cloud and showers; stable air produces stratiform cloud and steady precipitation.
- Fronts: cold fronts bring rapid lifting and squall lines; warm fronts bring gradual cloud and drizzle; occluded fronts combine both.
- Icing: most serious in freezing rain or cumuliform cloud at 0 to −20°C; avoid if possible.
- Japan: northwest winter monsoon brings snow to the Sea of Japan side; Baiu brings heavy rain in June–July; typhoons bring strong winds and torrential rain in late summer.
Worked example
Surface temperature is 20°C and dewpoint 14°C. The spread is 6°C. A useful convective cloud-base rule is 400 ft per 1°C of spread: 6 × 400 = 2,400 ft AGL. The reasoning: rising air cools at about 2°C per 1,000 ft until it reaches the dewpoint, so the spread tells you how high the lift must go before saturation. The result is a base, not a top; instability determines vertical development.
Traps
Do not apply the 400-ft rule to stratiform cloud or frontal fog. Distinguish AGL from MSL. A METAR is an observation, not a forecast; check the trend and TAF. Do not confuse QNH with QFE when reading station pressure.