9:30 p.m. update: D.C.’s eastern suburbs are now getting pounded with torrential rain and hail. Meanwhile, a flash flood warning is in effect until 12:30 a.m. for a portion of lower Montgomery County including Potomac, North Bethesda, Rockville and Aspen Hill. Water rescues are reported ongoing with cars stalled in standing water in this area, where up to 3 inches of rain has fallen.
9:15 p.m. update: Storms have waned to the west and south of D.C. But inside the Beltway and to the north and east we’re still seeing torrential rains, lightning and significant hail. The worst of it should start to move away to the east-northeast over the next 45 minutes.
8:55 p.m. update: Much of the area inside the Beltway and to the east is under a severe thunderstorm warning until 9:30 p.m. Wind gusts of 60 mph are possible in addition to small hail, heavy rain and dangerous lightning. Arlington, most of the District, and much of northern Prince George’s County are included in the warning area.
8:30 p.m. update: As we transition away from the severe weather threat, torrential rain and lightning are presently the main risks around the area.
There is a break in the action, though. And activity working this way from the southwest has waned a bit as well. We should see more rain tonight, but some spots could see an extended break through the late evening.
8:05 p.m. update: Severe weather is beginning to wane as we get deeper into the evening. While the severe weather was somewhat isolated, the few powerhouse storms that developed earlier are known as supercells. Much more common in the central United States, supercells occur perhaps a once or twice a year in the broader region. Supercells are known for their powerful updrafts, and that helps them produce very large hail. This evening’s were no exception.
Bob Leffler, a retired National Weather Service climatologist, shared pictures with us that his son Brett Leffler took in Rockville, Md. of this evening’s hail.
Others have reported similar:
Large hail is very unusual in any one location around here, but happens with roughly the same frequency of supercells in the broader region. Last year, massive hailstones fell in northern Maryland.
7:40 p.m. update: Severe thunderstorm warnings remain in effect for parts of the area. But the vast majority of the area is experiencing heavy storms with hail, dangerous lightning, heavy rain and strong winds. No sign of letting up soon as more storms approach from the west.
7:15 p.m. update: Severe storms with hail and strong winds continue to pepper the D.C. area, with more approaching from the west. Check out some of these hail shots…
7 p.m. update: A TORNADO WARNING has been issued for central Charles County until 7:30 p.m. including La Plata. Radar has indicated rotation with this storm that will be near Saint Charles around 7:05 p.m., Waldorf around 7:10 p.m. (although Waldorf is not currently within the tornado warning area), and La Plata around 7:15 p.m.
6:50 p.m. update: Severe thunderstorm warnings now to the north and to the south of D.C. Numerous reports of hail…
6:45 p.m .update: Impressive hail with storms moving through the area now…
6:30 p.m. update: Much of the metro area, just west and and just south of the District, is under a severe thunderstorm warning until 7-7:15 p.m. These storms could contain damaging winds and, impressively, golf-ball sized hail. Try to stay off the roads as these storms pass through.
5:52 p.m. update: The storm southwest of D.C. has intensified, prompting a severe thunderstorm warning through 6:30 p.m. for central Prince William County, including Manassas, and southern Fairfax County including Annandale, Burke, Springfield, and Lorton. Wind gusts to 60 mph and quarter-size hail are possible in this storm along with heavy rain and lightning. This storm may move into Arlington, Alexandria and the District between about 6:30 p.m. and 7 p.m.
5:40 p.m. update: The storms which extend southwest of the Beltway – from southwest of Manassas east to near Newington are headed east northeast and should push through the Beltway between 6 and 7 p.m. These storms are not severe at this time but contain some lightning and heavy downpours.
5:20 p.m. update: The severe thunderstorm watch has been extended to the D.C. metro region. Remember that a watch means conditions are favorable for the development of severe storms, stay alert. A warning, on the other hands, means a severe thunderstorm is imminent or happening – seek shelter.
The watch is in effect until 10 p.m. Scattered thunderstorms have begun to develop in D.C.’s southwest suburbs, heading east-northeast.
2:30 p.m. update: A severe thunderstorm watch has been posted for Charlottesville, Va., and areas to the west and southwest. Some intense storms are already firing up in southwest Virginia. There’s a chance that a watch is posted farther north later on. We’ll keep you posted.
Original post from 1:30 p.m.
After five straight days of overcast, the sun emerges this afternoon. But this sunshine is self-defeating, fueling the atmosphere for thunderstorm development this evening and tonight.
Locally, the main hazard from these storms is expected to be very heavy rain.
Timing and coverage: Scattered showers and storms 4-8 p.m.; Widespread showers and storms 8 p.m. through 2 a.m.
Movement: Southwest to northeast
Likely hazards: Very heavy rain (localized amounts of one to two inches or more possible), lightning, gusty winds
Possible hazards: Localized flash flooding, damaging winds, small hail
Unlikely hazards: Tornadoes and large hail
Confidence: Confidence is high that storms with heavy rain will develop by sunset. Whether storms become severe and produce damaging winds and hail is more uncertain.
The trigger for the storms is a cold front poised just west of the Washington region. A wave of low pressure developing along the front will draw warm, humid air into the area into this evening, giving rise to the needed instability for widespread showers and storms.
The National Weather Service Storm Prediction Center has placed areas west and southwest of District in a slight risk zone for possible severe thunderstorms. It is this region where the most heating and destabilization is likely to occur and thunderstorms are favored to be most intense. Damaging winds would be the main threat in this area.
The District and points east and north are in a marginal risk zone as a wedge of cooler air in place this morning and into the early afternoon limits instability and the potential storm strength.
While the most intense activity may stay south, widespread storms — some strong — are likely in the Washington region.
Short-range modeling suggests scattered storms starting to erupt between 4 and 6 p.m. and becoming widespread by 8 to 9 p.m.
Because the front is slow-moving, storms may train or develop over the same areas repeatedly, leading to locally heavy rainfall totals.
The HRRR model, shown below, simulates rainfall totals of one to two inches or more in the Washington region. The high-resolution NAM model (not shown) also forecasts a stripe of heavy rain (about one to three inches) through the Washington and Baltimore areas.
(Lower-resolution global models generally forecast about 0.5-1.0 inches).
The heaviest rain should taper off in the hours just after midnight, but scattered showers are likely to linger through Tuesday morning.
Ian Livingston contributed to this report.