timf, I'm sure there's some variation but last year when I dayhiked it on August 18th it was pretty doggone warm. I never even put a light jacket on - shirtsleeves all day. I think any time in August has great chance of being pretty warm. I watched the summit weather on-line just about every day through August, and it was nice almost every day.
Hmmm....my last August trip in '02, it was a balmy 9* F on the summit with 30 MPH winds. The weather is so unpredictable in the Sierra. It was a hell of lot warmer on the summit in May 2007...by about 30* F. I had with me I've had a trip where their was a 30% possibility on the first day and it rained all 4 days we were out.
You really have to be prepared for the worst or you can pay an awful price for your gram counting.
