Night Meteorology and Aerodrome Forecasts
METAR, TAF and trends
A METAR is an observation; a TAF is a forecast with a validity period. Learn the change groups: FM indicates a rapid change, BECMG a gradual change, TEMPO a temporary fluctuation, and PROB30/PROB40 a 30% or 40% probability. PROB groups are not the most likely forecast, and TEMPO conditions are not expected to persist for the whole period. Always read the forecast for your expected time of arrival, not the current weather.
Night-specific weather hazards
Clear, calm nights with a small temperature/dewpoint spread favour radiation fog and mist. Katabatic drainage flows cold air into valleys and can produce low cloud, wind shear or fog at aerodromes in basins. Inversions trap haze and smoke, reducing visibility. Thunderstorms are harder to see at night: lightning shows the cloud, but the visible structure does not. Icing risk increases in cloud at night because temperature often falls faster than expected.
Worked example
TAF: 18010KT 9999 SCT030 BECMG 2000/2100 4000 BR BKN008 TEMPO 2100/2400 1500 FG. Your ETA is 2230. Reasoning: the BECMG means conditions become 4,000 m mist and 800 ft broken by 22:30; TEMPO adds a temporary 1,500 m fog. Plan for an instrument approach, a nearby alternate with better conditions, and holding fuel.
Traps
Reading a TEMPO as permanent; ignoring PROB; using the destination TAF for the alternate; and assuming a clear night will stay clear when the dewpoint spread is 1°C.