It's call "Indian Summer". I'm not sure if that's suppose to be a racial slur or anything, or if using that term is politically correct - but fuck it.
Oh, wait maybe, "Native American Summer". Fucking PC.
Anyways, sometime in Late October/Early November in which there is a period of time that is ridiculously warmer and then gets awesomely cold.
It tricks you - just like how a sunny day tricks you in the winter. One looks outside - sees the sun and goes, "Yay, it'll be warm." But no, the harsh wind burrows deep into your soul and freezes you instantly.