Squall line passes D.C. area; some trees down in St. Mary’s co.


Radar & lightning: Latest D.C. area radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

Update: 1:25 p.m., the tornado watch was discontinued for the D.C. region as the threat of severe weather has passed, even as some downpours linger – see below for additional updates through 2 p.m.

Overview: A line of showers and storms, which resulted in over 300 reports of severe weather from east Texas to West Virginia Thursday, will race through the D.C. region over between about 10 a.m. and 2 p.m. We expect heavy rains and some gusty wind as the squall line passes, but the line has weakened some since yesterday. Still, the line has shown some signs of re-generating, and the National Weather Service Storm Prediction Center has issued a tornado watch through 5 p.m. for a part of the Mid-Atlantic, including the D.C. area.  See map below.


Area shaded in red under tornado watch through 5 p.m. (National Weather Service)

This is a low-end tornado watch. The Storm Prediction Center says there is a just a 30 percent chance of 2 or more tornadoes in the above watch area, and a 20 percent chance of a strong tornado (EF2-EF5 in intensity). However, it does indicate an 80 percent chance of at least 10 severe wind reports in the watch area, although those should be focused more east and southeast of the District.

Remember a tornado WATCH means conditions *could* cause tornadoes to develop, be alert. A WARNING means a tornado has been detected and/or spotted, take action (go to the lowest level of a well-built structure, away from windows – put as many walls between you and the outside as possible).

Follow below for the latest updates.

2:00 p.m. update: A stubborn last area of showers along I-95 – from around Dumfries to Baltimore – is slowly pushing northeast, and should exit the area by around 2:30 p.m. or so. This is the last update.

Here is a video round-up on the storms that hit the Midwest and South yesterday, courtesy of this same weather system:

Storms damaged schools and other buildings throughout midwest and southeast states, with more possible on Friday. (Reuters)

1:35 p.m. update: More and more reports of downed trees are coming out of St. Mary’s County where it’s possible a tornado touched down.  It won’t be known affirmatively until the National Weather Service conducts a storm survey – likely in the next day.

12:55 p.m. update:  The threat of tornadoes and severe weather has ended in the metro region.  Severe weather largely eluded the immediate metro region, but there have been some reports of downed trees in St. Mary’s County. Some trailing showers have developed behind the first main line, mainly northwest of the District, but this activity is not at all hazardous.  Over the next hour or so, isolated to scattered showers are possible in the region, with clearing skies after 2 p.m. from southwest to northeast.  It will turn quite breezy, with winds from the northwest at 10-20 mph, gusting over 30 mph at times.  Temperatures will slowly fall through the 50s this afternoon.  Here are a couple photos from the storm:

 

 

12:38 p.m. update:  The tornado watch has been discontinued in D.C. region except in southern Maryland, where it will likely be peeled back by 1 p.m. or so. It remains in effect south and east of this region.

12:30 p.m. update: TORNADO WARNING for central St. Mary’s and southeast Calvert counties through 1:15 p.m. At 12:24 p.m. radar detected possible tornado near Leonardtown moving northeast at 60 mph, could impact California, Lusby and Calvert Cliffs. Take cover in this area. Threat will pass by 12:45 p.m. as storms are moving so quickly.

12:22 p.m. update: Along and west of I-95, the storms are more or less done. An isolated trailing shower cannot be ruled out – but that will be the exception. Skies are already brightening in many locations, with skies rapidly clear after 1 p.m. or so.

12:15 p.m. update: Severe t’storm warning for St. Mary’s and southern Calvert counties til 1:15 p.m. Storms may producing small hail and wind gusts over 60 mph. Storms will race through region at 65 mph over next 30 minutes.

12:10 p.m. update: For folks in the northern neck of Va - TORNADO WARNING for NW Essex County, NW Richmond County, and Central Westmoreland County through 12:30 p.m. Doppler radar indicated possible tornado near Champlain at 11:59 a.m. racing northeast at 55 mph. Folks in St. Mary’s County should carefully watch this storm, as it could head into that area.

12:08 p.m. update: Baltimore about to get blitzed. Severe thunderstorm warning for eastern Howard County, Baltimore County, northern Anne Arundel County and the city of Baltimore through 1 p.m. Damaging winds over 58 mph poss in this line.

12:03 p.m. update: Line fell apart in the District, with just light to moderate showers. The strongest section of the line is north of the Beltway from Beltsville to Columbia to just east of Reisterstown and it’s racing east-northeast towards Elkridge and Catonsville.

11:55 a.m. update: These storms are moving so fast hard to keep up – steam-rolling east at 50 mph. They are already east of I-95 in Virginia, well into the District, and zipping through eastern Montgomery and central Howard counties. Still no reports of severe weather.

11:50 a.m. update: Storms are intensifying as they reach northwest D.C. and southern Montgomery County. Wind gusts to 40+ mph possible along with very heavy rain.

11:45 a.m update: Storms have moved inside the Beltway, shouldreach the District between 11:55 a.m. and 12:05 p.m. with some downpours – just in time for lunch. These storms are trucking and won’t stay over one area more than 30 minutes, really limiting their rainfall output. Still no reports of severe weather, but a rumble of thunder and gusty winds are still possible.

 

11:36 a.m. update: Some reports of thunder accompanying the storms as the roll through central and northern Fairfax County. Storms moving inside Beltway next 10 minutes.

 

11:28 a.m. update: Areas from Clifton to Fairfax to Rockville are next up with this line of storms – between now and noon. Still no reports of severe weather, but an isolated strong gust of 30-50+ mph cannot be ruled out.

11:19 a.m. update: Storms are now moving into western Fairfax County and Manassas, where very heavy rains and gusty winds are likely. Ahead of the storms, temperatures have spiked into the low-to-mid 60s in the District.

11:05 a.m. update: The squall line has advanced into western Montgomery County through eastern Loudoun County and into central Fauquier county. There are some breaks in the line – so some people may see little more than a brief gusty shower. So far, no reports of any severe weather, but some of the cells in central Virginia towards southern Fauquier and Prince Willam counties, moving northeast, look like they have potential to become more intense. We’re still looking at an arrival just before noon inside the Beltway.

10:59 a.m. update: From Capital Weather Gang severe weather expert Jeff Halverson: “I just looked at an analysis that shows significant amounts of low-level spin (helicity) along the warm front draped across D.C., just ahead of the convective line. You start getting concerned when the value is over 300 and we are at 450. This is one of the reasons SPC issued the watch…the other being the likelihood of bowing line segments developing further east and south this afternoon. Bow echoes can generate tornadoes. Keep in mind DC is right along the ragged edge of this watch – I still think areas south and east of DC are at higher risk.”

10:35 a.m. update: While we’ll deal with some heavy downpours and gusty winds as the showers/storms roll through, the nasty, more dangerous weather is in east central North Carolina, where a tornado watch is in effect through 4 p.m. Look at the intensity of the storms on radar there, below:

Radar view just after 10 a.m. and tornado watch area (outlined in red). (NWS SPC)
Radar view just after 10 a.m. and tornado watch area (outlined in red). (NWS SPC)

10:25 a.m. update: As downpours reach Frederick, Maryland, temperatures are surging ahead of the front in Fredericksburg, Virginia – where a Twitter follower reports it’s 70 degrees. Those temps will help fuel the line east and southeast of the District.

10:10 a.m. update: Showers/storms already moving into western Loudoun and Frederick counties.  Winds up at about 3,000 feet, per CWG severe weather expert Jeff Halverson, are blowing at 70 mph: “so it won’t take too strong a downdraft to bring high gusts to the surface.”  Strong winds at this altitude stretch well to our south through central Virginia into the Carolinas.

 

10:00 a.m. update: The wedge of cool air is eroding, as a warm front lifts northward.  The warmer air coming in will help energize the line of showers/storms running into it, but the window for heating is limited to just a couple hours in the immediate D.C. area, slightly longer to the east and southeast, where activity may become a bit more intense.


The movement of fronts and radar over the last several hours (MarylandWx.com)

9:45 a.m. update: Based on the latest short range models, the line should arrive along the I-81 corridor just before 10 a.m. (i.e. now), inside the Beltway near noon, and cross the Chesapeake Bay by 2 p.m. Watch the animation here:


HRRR model animation of squall line between 10 a.m. and 2 p.m. (WeatherBell.com, adapated by CWG)
Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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