When it has to be clean, but it’s 110 in the shade…. (Auto Detailing Tips From A Professional)
While generally not desired, it’s not impossible to wash a car in hot weather without damage.
It’s all in the thought process and preparation. Which could start as early as first thing in the morning, probably one of the best times one could choose during hot summers to get in a wash but if you aren’t an early bird, the other option might be sharing a beautiful sunset with your ride while you wash.