You'll find Alaska's summer temperatures surprisingly pleasant. Daytime highs range from 60°F - 80°F. Nighttime lows are refreshingly cool, dipping into the 40's - 50's. May and September are 5°- 10° cooler. However, temperatures vary wildly depending on which region of Alaska you plan to visit.ain. On average, Alaska's summers are slightly rainier than the rest of the U.S. But May is dry, with only a 25% chance of measurable rain on any given day. Alaska gets rainier as the summer progresses. By August, the chance of rain is just over 50%.Compare Alaska's rainfall to your hometown.