Amarillo is pretty far north from where I grew up in Houston. I have been there before and remember the weather being cool. It's getting up in the hill country and they have a much more temperate climate there. They even get snow pretty regular.
I guess I should amend my statements to mid and south Texas.
A chilly (and windy) autumn evening yesterday, in the old town in the neighbourhood. (Actually, I've been there to take some photos from the "Illuminata" - a light installation in the old town, along the river Ems, in some parks and on a lake.)