This is classic down-slope warming. As air descends, it warms up. First law of thermodynamics. When the wind comes from the west, the D.C. metro tends to be warmer because air is flowing down off the mountains. All three airports set new records for the date.
Feb. 8 records
68 degrees (1900) → 74 degrees (2017)
70 degrees (1965) → 72 degrees (2017)
70 degrees (1965) → 71 degrees (2017)
So far this winter, warm days have far outnumbered the cool ones.
Brace for a change, though. At 10 a.m. tomorrow, the temperature will have dropped 30 degrees in the D.C. metro. By Friday morning, it will be 40 degrees cooler.