The showers and storms should first enter the region from west to east between about 4 and 8 p.m. and then exit during the predawn hours Wednesday.
The National Weather Service’s Weather Prediction Center is calling for a “moderate to heavy precipitation event” and has placed much of the region in a slight risk zone for excessive rainfall.
Models are forecasting about 0.5 to 1.5 inches of rain, although some higher amounts are possible where the heaviest downpours focus. Some models suggest the heaviest rain in the mountains and east of Interstate 95 while the more intense and persistent downpours skip over the immediate area.
Here are predicted amounts for Washington from different models: American (GFS): 0.9 inches; Canadian: 0.6 inches; High-resolution Canadian: 0.5 inches; European: 0.6 inches; HRRR: 1.0 inches; High-resolution NAM: 0.4 inches; NAM: 0.3 inches; and UK Met: 0.8 inches.
Any thunderstorms that develop would probably come through between the late afternoon and evening, before transitioning into more of a general rain.
“The expectation is that severe thunderstorms shouldn’t be a major issue today, but there is a non-zero threat for some damaging winds if stronger storms are able to form,” wrote the National Weather Service forecast office in Sterling, Va.
The Weather Service’s Storm Prediction Center places the southern part of our region in a marginal risk (level 1 out of 5) zone for severe thunderstorms.
“Very strong, deep shear (increase in winds with altitude) conditions our region for a low-end threat of strong to severe thunderstorms,” wrote Jeff Halverson, Capital Weather Gang’s severe weather expert. “However, the atmosphere will not be very unstable, given the thick overcast and weak decrease in temperature with altitude. Any thunderstorm wind damage will be spotty at best, and the biggest threat lies to the south of D.C.”
The threat of inclement weather comes as Washington’s primary weather radar in Sterling is out of service. Forecasters will be forced to rely on less powerful and more distant radars to monitor storminess.