Ingredients are coming together for a severe weather threat late today/early tonight in the Mid-Atlantic region extending from the Philly and DC metro regions on the west side to southern New Jersey and the Delmarva Peninsula on the east. Vigorous upper-level energy will swing from southwest-to-northeast and across the region late today/early tonight and that will cool off the upper part of the atmosphere. This upper feature will combine with increasingly warm and already-moist low-level air to destabilize the atmosphere significantly late today/early tonight which will allow for the possibility of severe thunderstorm activity.
One parameter that is followed by meteorologists for determining the overall stability of the atmosphere is called the Convective Available Potential Energy. It is already quite high this afternoon across the Delmarva Peninsula indicating some instability and it has been increasing noticeably in that area over the last three hours. Clouds have broken to allow for some sunshine over the Delmarva Peninsula in recent hours and this clearing zone should expand during the next few hours; especially, to the south of the PA/MD border. Any sunshine this afternoon will help to destabilize the atmosphere and increase chances for strong-to-severe thunderstorms.
The best chance for showers and strong-to-severe thunderstorms will likely come between around 4pm and 10pm with the precipitation swinging from southwest-to-northeast (e.g., DC gets hit before NYC). Stay tuned…there are no severe thunderstorm watches at this time from the NWS, but I expect that’ll happen later today (maybe even a tornado watch). Any thunderstorm can produce heavy rain, damaging wind gusts, hail, and isolated tornadoes are even a threat.
Meteorologist Paul Dorian