Clouds and thunderstorms

Clouds are named by height and shape: cirrus (high, wispy ice), alto- (middle), stratus (layers), cumulus (heaps) and nimbus (rain).

The most dangerous cloud for aircraft is the cumulonimbus (Cb) thunderstorm: strong up- and down-draughts, severe turbulence, hail, icing, lightning, heavy rain and microbursts near the ground. Pilots keep well clear (often 10–20 NM).

Malaysia has two monsoons: the Northeast Monsoon (about November to March, heavy rain on the east coast of the Peninsula, Sabah and Sarawak) and the Southwest Monsoon (about May to September, drier). Afternoon and evening thunderstorms are common all year, and early-morning Sumatras (squall lines) can cross the Straits of Malacca.