I'm not stranger to mild temperatures for Christmas. In fact — I've never had a white Christmas; remember I'm from Louisiana :)
I decided to do a bit of research and I discovered that over the last 100 years, Maryland has only reached/topped 60° on Christmas ten times! Last year was our most recent occurrence, where we reached 60°! The forecast this year calls for temperatures to reach 65°, and if it does, we will tie 1965's Christmas for 5th warmest Christmas! We can thank strong southerly flow for our warmup— winds will be gusting 30+ mph.
A few early morning sprinkles will be possible, the bulk of that moisture looks to be confined to areas along and east/south of I-95. An isolated lunchtime shower will be possible as well, but I expect the bulk of the rain to trickle in late afternoon early evening as the cold front is making its final approach.
Rain totals will not be overwhelming with most areas picking up up to a quarter inch. Isolated locations may pick up to a half inch. The rain couldn't come at a better time, being that we are sitting 2.67" below average for the month of December.