It's about to rain.
'Piovere' — PIO-ve-re. Three syllables, stress on the first. 'Sta per' = is about to (stare + per + infinitive).
Use when clouds are gathering and rain seems imminent. Practical and useful — it prompts people to get an umbrella or move inside.
'Stare per' + infinitive expresses the near future — something that is about to happen. 'Sta per piovere' (it's about to rain) is a key weather phrase combining this construction with one of Italy's most discussed weather phenomena.
Si sta coprendo.
It's clouding over.
Describes the process of clouds forming — a warning sign
Sembra che voglia piovere.
It looks like it wants to rain.
Personifies rain using 'volere' — very poetic and natural in Italian
Arriva un temporale.
A storm is coming.
'Temporale' = thunderstorm — more severe than rain alone
Italians carry umbrellas ('ombrelli') as a matter of course. 'Prendi l'ombrello' (take your umbrella) is one of the most common things Italian parents say to children before they leave the house, regardless of apparent sky conditions.