Environment Canada has issued a flash freeze warning for most of mainland Nova Scotia. Heavy rains are expected to give way to rapidly plunging temperatures Saturday.The weather agency says temperatures will dip to around –10 C by this evening."Untreated surfaces such as highways, roads, walkways, and parking lots may become icy, slippery, and hazardous," it said. "Be prepared to adjust your driving with changing road conditions."Flash freeze warnings are in effect for Colchester, Cumberland, Ha