It actually can get pretty chilly during July. I like to stick with the tall tee and hoodie combo, With just a t-shirt you might get a little cold. It really depends on the day though. You don't need a jacket for sure.
i can get pretty balmy in marmot... the town that windels is kinda in... not really sure.. but it can get down right crotch rotting hot in the summer time there.. and the bees.. oh god dont go near their honey!
I read this in Freeze, "It can be hotter than two rats humping in a wool sock, or colder that a witch's teat." After two summers there, it could not be more true.