Grabbed this off wikipedia for 1981-2010 averages at DCA. Looks like February is in fact the driest month of the year, on average. You sure about your statement?
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Average precipitation inches (mm)
2.81
(71.4)
2.62
(66.5)
3.48
(88.4)
3.06
(77.7)
3.99
(101.3)
3.78
(96)
3.73
(94.7)
2.93
(74.4)
3.72
(94.5)
3.40
(86.4)
3.17
(80.5)
3.05
(77.5)
39.74
(1,009.4)