Agreed with all the advice you've gotten so far, with the exception of Carol's statement that "If there is a snow, be prepared for the fact that the DC area doesn't always handle it well."
If there's snow, D.C. doesn't EVER handle it well. This town is pathetic in wintry weather. Schools have closed based on the threat of receiving snow, and accumulations on the roads of two or three inches have led to hours-long debilitating traffic jams. The good news for you is that you're near underground Metro stations -- that part of the system keeps running in snow, but even the above-ground stations in our subway system close for snow or ice from time to time.
Coming from Ottawa, if you're here at one of those times, you'll laugh and think we're the softest most pathetic creatures on the continent.