I meant that with a high, or even “normal” humidity level you know when you are sweating. In that Arizona sun the air is so dry that you never feel sweaty, it instantly evaporates, but being so hot it also doesn’t act to really cool the body as intended. So it feels like you’re not sweating, potentially leading some to push harder not knowing how dehydrated they actually are until it’s too late.
I think of it like the boiled frog, only instead of boiling in water you are slowly losing water you don’t even feel leaving you.