Good morning, D.C. Today will be fairly rainy but not too cold, though temperatures are expected to drop significantly late tonight. Don’t hold your hopes out for a white Christmas, though: the folks over at CapitalWeather tell us there’s only a 15% chance of that happening. And if you’re traveling for the holidays, be careful: more than one million area people are going with you. You can read a Post chat transcript with the AAA…