(This story, originally posted at 10:23 a.m., and was updated as storms moved through the D.C. area)

2:40 p.m. final update: Storms have now exited Washington’s eastern suburbs and are headed over the Chesapeake Bay. In the immediate metro area, they were generally less severe than feared. However, there were pockets of damaging winds around in Montgomery County and the District.


Graphic showing reports of tree damage (tree icons) and high wind gusts (wind icon from around the region, logged by the National Weather Service, March 1, 2017.)

The more extensive area of high winds focused south and east of the District in Prince William, Stafford, Prince George’s and Stafford counties.

The storms produced some impressive peak wind gusts, including:

Quantico, Va.: 78 mph
Germantown, Md: 66 mph
Andrews Air Force Base: 62 mph
King George: 61 mph
Capitol Hill: 58 mph
Gaithersburg: 58 mph
Clarksburg, Md.: 58 mph
Seat Pleasant, Md.: 58 mph
Bowie, Md.: 58 mph
Suitland, Md.: 58 mph
Reagan National Airport: 54 mph

For the rest of the afternoon, we should be mostly cloudy and breezy (gusts to 20-30 mph), with temperatures between about 70 and 75 degrees. A few pop-up showers are possible.

(Scroll to bottom of posts for earlier updates that are now expired.)


Original post


Area under severe thunderstorm watch in blue.

A powerful line of thunderstorms, with the potential to unleash damaging winds, is forecast to blast through the D.C. area this afternoon between about 1 and 4 p.m.

If the squall line reaches its full potential, damaging winds could be widespread. However, storms may be less intense in areas where sunshine  — which acts as fuel for the storms — is more limited.

Just after 11 a.m., however, satellite imagery showed increasing sunshine from the District south.

The National Weather Service has issued a severe thunderstorm watch, meaning conditions are favorable for severe storm development, but not a guarantee. Stay alert.


Timing: 1 p.m. through 4 p.m., but storms will only last 30 minutes or so in any particular area.
Coverage: About 70 percent of the area should experience storminess.
Hazards: Areas of damaging winds, lightning and heavy rain are likely. Small hail is possible. Isolated large hail and a weak tornado or two cannot be ruled out.
Storm motion: West to east

Note: A second broken line of showers and maybe thunderstorms is possible between about 10 p.m. and midnight, but probably will not be severe.

As the afternoon line of storms moves through, if severe thunderstorms warnings are issued, seek shelter in a strong building and stay off the roads if possible. Bring inside outdoor furniture or any item that could become a dangerous projectile.

Scattered power outages are possible, so charge portable devices.


The National Weather Service Storm Prediction Center has placed the region in an enhanced risk zone for severe thunderstorms. This is level three on its 1 to 5 scale.

Notably, it forecasts a 45 percent likelihood of damaging winds within 25 miles of a given point in our region, which is a very high number. During our typical severe thunderstorm threats, that likelihood is placed at 15 percent.


Likelihood of damaging winds within 25 miles of a point on Wednesday. (National Weather Service)

Discussion

The storm system predicted to generate these dangerous storm is the same one which resulted in more than 500 reports of severe weather Tuesday in the Heartland. These reports included 24 tornadoes, 243 incidents of damaging winds, and 250 instances of large hail.

The storms were responsible for three deaths, CNN reported.

The storms are forming ahead of a powerful cold front, stretching from the Great Lakes to the Deep South. On Wednesday morning, severe storms were lined up along the Ohio-West Virginia border southward through Tennessee.

Extremely powerful high-altitude winds are helping to power and sustain the storms as they march eastward.

As the storms cross the mountains, the key uncertainty is how well they hold together. Early Wednesday morning, a stubborn cloud deck was holding back temperatures in the D.C. area whereas sunshine and warm temperatures are needed to energize the storms.


Radar simulation between noon and 3 p.m. from HRRR model.

By late Wednesday morning, however, sunshine was emerging  — increasing the potential for storms to erupt and turn dangerous.

We will provide updates through the afternoon on this developing situation.


Expired updates

Estimated arrival time for storms: Leesburg and Frederick 1:00-1:20 p.m. | Fairfax and Rockville 1:20-1:40 p.m. | The District 1:35-1:55 p.m. | Baltimore, Laurel, and La Plata: 1:50-2:10 p.m. | Annapolis: 2-2:20 p.m.

2:10 p.m. update: Severe thunderstorm warnings have been dropped inside the Beltway and to the west, but intense storms continue from Annapolis to eastern Prince George’s and Charles counties. These storms are headed into Calvert and St. Mary’s counties and will pass through over the next 30 minutes.

1:57 p.m. update: Radar shows storms have progressed east of Interstate 95 and are consolidating into a pretty powerful line from just south of Baltimore to around Colonial Beach. Andrews Air Force Base just clocked a wind gusts of 60 mphSevere thunderstorm warnings are in effect for all of D.C.’s eastern suburbs through 2:30-2:45 p.m.

1:40 p.m. update:  While storms in the immediate metro area have been pretty ordinary, they are intense from southern Prince William County through eastern Stafford County. Charles County should expect areas of damaging winds as these storms come through over the next half hour. A severe thunderstorm warning is in effect for Charles, Calvert and St. Mary’s county through 2:30 p.m.


Radar snap shot showing intense storms about to enter Charles County, Md at 1:40 p.m. (Weather Underground)

1:30 p.m. update: Storms are now arriving on the west side of the Beltway and will hit the District in the next 20 minutes. Thus far, we have not seen reports of damaging winds in the immediate region but storms could intensify.

The strongest storms in the region, at the moment,  are north of town in southeast Frederick County headed towards Damascus and Mt. Airy and south of Dale City in Virginia.

1:10 p.m. update:  In addition to the warning for the immediate metro area, a severe thunderstorm warning has been issued for all of Washington’s northern suburbs from Rockville, Md. to the Pennsylvania border through 2 p.m..  Winds may gust up to 60 mph or so as these storms pass.  Radar shows a particularly intense area of wind and rain moving into Frederick, Md.

1:07 p.m. update: A severe thunderstorm warning has been issued for all of the Beltway, the District, Fairfax, Prince William and Stafford counties, as well as western Prince George’s and Charles counties. Storms are racing eastward and may pack winds of 60 mph. They will not last particularly long, passing over a period of 15 to 30 minutes or so. But they may knock some trees down and cause some localized power outages.

The warning expires at 1:45 p.m. but may need to be extended a bit for the easternmost areas.

12:54 p.m. update: The National Weather Service has issued a special statement highlighting the likelihood of “dangerous and damaging” wind gusts in the Washington and Baltimore areas. “Get indoors and be ready for power outages,” it warns. “This will likely down trees and be a threat to those outdoors.”

12:45 p.m. update: A severe thunderstorm warning has been posted for northern Loudoun and western Frederick (Md.) counties, and includes Leesburg and Frederick. It’s in effect through 1:30 p.m. Wind gusts to 60 mph and small hail are possible in this storm.

12:30 p.m. update: A severe thunderstorm warning has been posted for much of Fauquier County and southern Loudoun County, including Middleburg and Warrenton. Winds may gust to 60 mph as these storms dart through the region in the next 45 minutes (warning expires at 1:15 p.m.)

12:25 p.m. update: These storms are really moving and should enter D.C.’s far western suburbs, including Loudoun, Frederick, and Fauquier counties between 12:30 and 1 p.m. and may enter the Beltway between around 1:30 and 2 p.m. As the storms below through Harrisonburg, winds gusted to 58 mph. A weather station in Allegany County, Maryland also clocked a gust to 58 mph.

12:15 p.m. update: Storms are racing east out of West Virginia into western Virginia at a clip of around 50 mph. Severe thunderstorm warnings (in effect until 12:45 p.m.) cover the Interstate 81 corridor from around Martinsburg to Staunton in west central Va., and includes Harrisonburg, Luray, Strasburg, and Winchester in Virginia. Wind gusts to 60 mph are possible in these storms.