For 3 weeks, it shouldn't be too bad. It's easy enough to disconnect the battery, but I don't think you'll need to. I've let my People 50 sit for over a month in the cold without starting it, though it was stored in a building. It took a couple extra turns to get it to start, but all in all it wasn't a big deal.
I used to live up your way, in Fredericksburg Virginia. Spent a lot of time in Falls Church too.
Cheers!
~Josh