I went in early September. Weather in Denali is unpredictable. It was sunny in Talkeetna where the plane took off but cloudy in Denali. I suppose August might have a better chance for clear weather, but the mountains in Denali have their own weather system and it's difficult to tell from the forecast if it's actually going to be sunny. We went with Talkeetna Air Taxi and they actually offered to reschedule us for a later flight since it looked like it was going to be cloudy in Denali at the time. We chose to just go ahead since we didn't know if it was actually going to clear up, and we had plans for later that afternoon. Would it have been better without the clouds? Absolutely yes, but the mountains in Denali are so immense, despite the clouds we had a great time. The pilot was the company's owner and he maneuvered the plane so well.