What terrible weather!
'Tempaccio' — tem-PAC-cio. The '-accio' suffix adds negativity. Stress on the second syllable.
Use on grey, rainy, or unpleasant days. The '-accio' suffix transforms 'tempo' (weather) into something strongly negative — a very Italian linguistic trick.
The suffix '-accio' (feminine '-accia') is a 'peggiorativo' (pejorative suffix) in Italian, making a word express badness or ugliness. 'Tempo' (weather) → 'tempaccio' (terrible weather). 'Giornata' → 'giornataccia' (awful day). This is productive Italian morphology.
Che giornataccia!
What a terrible day!
Extends the pejorative to the whole day — even more dramatic
Un tempo da lupi.
Wolf-like weather.
Idiomatic — 'un tempo da lupi' means weather so bad only wolves go out in it
Il tempo fa schifo oggi.
The weather is dreadful today.
'Fa schifo' (makes disgust) = is disgusting/awful — very colloquial, avoid with elders
Italian spring ('la primavera') is famous for its unpredictability — sun and heavy rain can alternate within hours. 'La primavera è pazza' (spring is crazy) is a common Italian saying that perfectly captures the season's mood swings.