I live in Chicago and have a 10 mile commute via my SRAM S7 IGH.
I noticed this past week with temperatures dropping well below freezing all of a sudden, my shifting became substantially less crisp. This happened last year too, but I just attributed it to wearing bulky gloves. Well, the difference this year is that it wasn't just mushy, but it gets entirely stuck. If I downshift (it's a twist shifter if you're unfamiliar), the housing comes out of the shifter and of course the gears don't actually change. It does start clicking and slipping and being terribly unruly.
This only happens after I've been out riding for maybe 20 minutes. Once I bring my bike inside, it starts working again normally very soon. So, I'm quite sure something is freezing, but the question is, what? Follow up question would be what is to be done?