The trigger for the storms is a slow-moving cold front stretching from southern Pennsylvania to the Florida panhandle. NOAA has placed the the D.C. area and points south under a slight risk of severe storms and says there’s a 60 percent chance it will issue a severe thunderstorm watch.
Widely scattered showers and storms have already developed to our south and should increase in coverage and intensity between 3 and 5 p.m. as they head east and northeast and new storms develop.
As it stands now, the most intense activity in the D.C. area may occur between 5 and 8 p.m. My take on the situation is that any severe storms will probably be isolated around here, with better chances for damaging winds and large hail south and southeast of metro D.C. Nevertheless, some strong storms with heavy rain, gusty winds and dangerous lightning are certainly possible here.
Above is a high resolution model simulation of the radar between and 3 p.m. this afternoon and 2 a.m. tonight. It shows the evolution of widely scattered thunderstorms into developing lines of showers and storms propagating from southwest to northeast. After dark, the lines of storms merge into an area of general rain, with possible embedded storms.
This simulation gives a general sense of possible rain and storm development and may not have the details and timing exactly right. I think it also is overdoing the storm coverage. But it does show considerable potential for widespread showers and storms this evening.
Note that not everyone will get hit - I’d give about 60-70 percent odds of rain at any given location.
Rainfall potential and amounts so far
Rainfall amounts with developing storms will be highly variable, but an additional 0.5-0.75” of rain is certainly possible.
Here are rainfall amounts since Monday at the three airports:
Reagan National (DCA): 1.32”
Dulles (IAD): 1.1”
Rainfall records for today are:
DCA: 1.28” (1949)
IAD: 2.40” (2003)
BWI: 1.83” (1892)
With 1.08” so far today, Reagan National has a good chance to set a daily record.