。。
The sky looks ominous. Wonder if it's going to rain.
Literal
Sky [subject-が] suspicious. Rain [subject-が] fall [I-wonder-かな].
A casual weather-watching moment. 怪しい is the standard adjective for 'suspicious, strange, sketchy,' but applied to 空 ('sky'), it specifically means 'ominous, threatening,' suggesting bad weather on the way. This collocation 空が怪しい is a set expression in everyday weather-watching language. The second sentence ends in 降るかな ('I wonder if it'll fall'), with かな as the casual musing question particle. The two short sentences together sketch a small moment of amateur weather forecasting.