We went late in August. It was hot and very dry. I did not care. It was AWESOME and the Virgin River made for a lovely cooling off spot. Go when you can!
Went a week ago and despite daily rain showers it was very enjoyable. Camping on BLM land nearby is accessible and not crowded. Views were stunning, even under clouds. Hiked Angel's landing and the west rim. There was snow up on the kolob side. Since then have seen that were hours-long waits over memorial day weekend, and no parking for shuttles. Summer holiday weekends like the fourth are likely to be similar. From what I've read summer is the peak season, though I haven't been then. I'd shoot for fall as the best time if I had my pick. Dry and with good temps.
Way hot and crowded
We went last year at the end of July! It was warm, but thunderstorms came and went every other day and cooled everything down so it wasn't actually all that bad at all. The rain caused mud and rockslides that lead to several hiking trails being closed, that was a bunmer more than the temperature, actually.
Hi we went to Zion dltwo weeks ago and we had perfect weather. We did the Angel Landing trail. I guess August will be much hotter (28°+) and crowded. I would rather prefer to go then in September - October.
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