。
It started raining from evening on.
Literal
Evening-from rain [subject-が] fall-start-[past-した].
降り出す ('to start raining') is a compound verb fusing 降る ('to fall') and 出す ('to put out, begin') — the suffix ~出す is highly productive for marking the abrupt onset of an action. から here is the temporal 'from,' marking the starting point in time. Note that this same から particle also means 'because' in other contexts; here it's the simple time-source sense.