1:50 p.m. Update: The National Weather Service has issued a Severe Thunderstorm Watch for the D.C. area until 9 p.m. Hail to 1.5 inches in diameter and wind gusts to 70 mph in addition to dangerous lightning are possible with any storms that develop this afternoon into evening.
Area highlighted by Storm Predicton Center for highest potential of severe thunderstorms (NOAA Storm Prediction Center)

From 11:51 p.m.: A cold front sagging south from the Northeast this afternoon to the northern mid-Atlantic tonight - along with strong upper level winds - promises to trigger strong to severe thunderstorms across this area.

The favored area for the most severe weather is from southern Pennsylvania to central Massachusetts where the front’s passage will encounter the strongest upper level winds and peak day time heating.

Link: Northeast regional radar

As NOAA’s Storm Prediction Center notes:

THE BEST CHANCE FOR ORGANIZED/SUSTAINED ACTIVITY WOULD APPEAR TO BE OVER SRN NY/NRN/ERN PA INTO SRN NEW ENGLAND AND NJ...WHERE SMALL BOWING STRUCTURES AND POSSIBLY AN EMBEDDED SUPERCELL OR TWO WITH DAMAGING WIND MAY OCCUR IN ADDITION TO MARGINALLY SEVERE HAIL.

Probability of damaging winds within 25 miles of a given point. These are highest ofer southern New England but extend into the D.C. metro region (NOAA Storm Prediction Center) Nevertheless, some more widely scattered strong-to-severe storms are possible in the Washington, D.C. and Baltimore regions by late this afternoon and especially this evening.

Any storms that develop - given large amounts of instability (very hot temperatures and high moisture content locally) - are likely to produce very heavy rain and dangerous lightning. And we cannot rule out the possibility of some damaging winds in some of the storms.

We will keep you apprised of storm development and any watches or warnings issued.