Temperatures Friday afternoon climbed to the low 70s across most of the metro area, marking the first time in 16 days that a temperature surplus was observed. The exception was along the lake, where light onshore flow held the high at Northerly Island to 57 degrees. Warmer days lie ahead. June-level warmth is to reach the area Saturday and Sunday, but light west, to southwest winds will not be strong enough to negate the cooling influence of lake Michigan. As inland areas warm to around 80 degrees, cooler, denser air over the lake will prompt a frontal boundary to advance inland by late Saturday. East winds are to strengthen again Sunday causing lakeside temperatures in the low 70s to plummet as much as 20 degrees. Strengthening southwest winds are to lock in early next week bringing a stronger surge of tropical air.