So based on my analysis, and the various vectors relevant to current atmospheric conditions and trends (past, present, and future), I believe that the precipitation shield is traveling at approximately a 30 degree northeasterly angle relative to the magnetic poles (not accounting for flat map distortion or curvature of the earth). Therefore, based on the observable rates and airborne buoys engineered for data collection purposes, in addition to geometric conditions, the immediate D.C. area, including areas slightly north, south, east, and west at varying distances from a central radius, should expect somewhere in the area of 16" to 20" inches.
Of rain.