I obviously got lucky on my visits to Claremont. I was there when the big wildfires were raging, north of LA, and I was prepared for horrible air quality. As it turned out, it was so clear that I could literally stargaze from my Airbnb.
My kids both did summer programs in Claremont, when they were in HS, and the heat was pretty brutal; but once my Scripps kid got to college, the weather was nice for most of the year, although there were certainly times (especially at the beginning of the school year) when everyone was grateful that the dorms had been retrofitted with AC. I’ve never thought of it as a “rule it out because of heat” kind of place, though; it’s hardly Phoenix, or Palm Desert. I don’t recall her being bothered by air quality issues, either. She just missed cool, rainy days, and was happy to land in the PNW after college.