There seems to be less snow and rainfall within the beltway (note the difference between Dulles and Washignton National). I imagine its because of the cumulative effect of all the concrete and pollution. You can see the weather patterns on the time lapse Doppler kind of steer around the beltway many times. We used to call Alexandria "the Planet," because it had a weather pattern like nothing around it, and we joked that they were conducting weather control experiments from the George Washington Masonic Memorial (that huge tower that looks something like the Washington Monument).