In other news, purequaternion, the sun will only reach zenith within the tropics (That's kinda the definition of the tropics) Sooooo what you're saying is a little off.
I personally had assumed it was russian tundra not american northwest, that would put it at closer to 60 degrees than 45. Though my second guess would actually be the alps (which also lie at 45). I think the reason for my assumption it was soviet alps is the timing of the introduction, the Heavy update. My mind formed an obvious link.
As far as the actual location goes, we can only say it's below 47 degrees latitude so american Northwest and actual Alps works great provided it's midsummer.
Someone should email Dhabih Eng and ask. (He is the artist responsible for the skybox in question I believe).