In reply to GridNorth: There's pretty much zero reliability to the weather, other than general trends. Last year it was 0 degrees; on June 1st, this year, 27 degrees;. And that was after a late arriving spring.
If there is one trend I've noticed over the years, it's that the weather often cycles from year to year. That is to say, last year was a pretty cool and stormy summer for the most part (20 degrees; was the highest temp last year), which means this year has a good chance to be fairly decent, especially if the trends from June continue.
You don't really have to worry about darkness until the end of August, so you can pretty much climb round the clock if need be.