Often used in compounds such as 悪天候 (bad weather) or 悪天時 (bad weather conditions). As a standalone noun, it is somewhat formal or written.
悪天のため、試合は中止になった。
The match was canceled due to bad weather.
悪天候が続
Bad weather continues.
Compound of 悪 (bad) and 天 (sky, weather). The exact historical derivation is uncertain, but the kanji combination directly conveys the meaning.