* Trees down, thousands without power across the D.C. region after severe storms move through *

9:50 p.m. — EF1 tornado confirmed in Columbia

The National Weather Service has confirmed a tornado touched down in Columbia at 3:34 p.m., tearing part of a roof off a building and snapping trees. It was rated EF1 on the 0 to 5 scale for tornado intensity.

The Weather Service will release more details on the tornado Friday.

5:20 p.m. — Severe storms exiting region with scores of wind damage reports in their wake

Radar shows the last of the storms pushing through southern St. Mary’s County and exiting the greater D.C. region, and the severe thunderstorm watch has been canceled for the immediate area. The storms packed a major punch as they came through.

Almost the entire region was under severe thunderstorm warnings late Thursday afternoon, while tornado warnings (now expired) were issued for Columbia, Md., and the District. There has been no confirmation of tornadoes, but the National Weather Service will evaluate damage from the storm and determine whether it was caused by tornadoes or straight-line winds.

The strongest winds seemed to come through east Falls Church and Arlington County. Reagan National Airport clocked wind gusts to 68 mph. Check out this dramatic video of a transformer exploding in Ballston (23 seconds into the video):

Damage reports from the storms are still coming, but here is a preliminary map that shows where most are clustered.


Wind damage reports through 5:15 p.m. on Thursday in Washington region. (Iowa State Mesonet)

We’ve received many photos of downed trees in Arlington and Falls Church, a few of which we share below.


Power lines downed by storm in Falls Church on Thursday. (Jane Chicaharito)

We will have a more detailed explainer and recap of these storms on Friday.

4:30 p.m. — Storms race through east and southeast suburbs

This nasty line of storms has exited the Beltway and now stretches from Annapolis, southwest through Calvert and Charles counties, and is pushing southeast at 35 mph. Severe thunderstorm warnings are in effect all along this line for the next 30 minutes or so. The storms continue to produce torrential rain, frequent lightning, and wind gusts to around 60 mph.

3:57 p.m. Tornado threat for District is over, winds gust to 68 mph at Reagan National; wind damage reported in Northern Virginia

Storms, many of which are severe, stretch from just southeast of Baltimore southwest through Mount Vernon to just east of Dale City. Wind gusts to 60 mph, lightning and heavy rain are the primary hazards.

The area of rotation which triggered the tornado warning for the District has weakened and moved off. There is no longer a tornado threat.

As the storms moved through Falls Church, Alexandria, and Arlington, they produced very high winds — which gusted to 68 mph at Reagan National Airport. In fact, Reagan National Airport clocked three gusts of at least 67 mph in the span of 7 minutes.

We have seen some damage reports starting to come in from this area.

3:49 p.m. TORNADO WARNING FOR DISTRICT until 4:15 p.m.

Seek shelter in interior rooms, away from windows ... in lowest level. Radar indicates possible tornado just south of downtown. Rotation is somewhat weak and diffuse, but strong winds are likely whether or not a tornado is on the ground.

(Scroll down to bottom of post for expired updates)

Original article from 1:25 p.m.

In less than 24 hours, our weather has switched from comfortably cool to summerlike and sticky. The new, humid air over Washington may fuel thunderstorms as a cool front approaches the region Thursday afternoon and early in the evening.

An unstable atmosphere and strong high-altitude winds heighten chances that some storms could turn severe with damaging wind gusts and hail.

The National Weather Service has issued a severe thunderstorm watch for the region until 8 p.m. A watch means conditions are favorable for the development of severe storms, but they are not guaranteed, and you should stay alert. But if a severe thunderstorm warning is issued for your location, it means a severe thunderstorm is imminent, and you should seek shelter.

The Weather Service watch says a few storms could produce scattered damaging wind gusts to around 70 mph and hail up to one inch across.

The storms may be hit or miss, with a greater concentration of them in our northern areas.

Storm dashboard


Approximate arrival time for storms:

  • 2 to 4 p.m. western areas
  • 3 to 5 p.m. immediate area, including the Capital Beltway
  • 3:30 to 5:30 p.m. areas east of Interstate 95

All clear: 6 to 8 p.m. from west to east

Storm duration: 30 to 45 minutes or so

Chance of measurable rainfall in any location: 40-60 percent (highest north, lowest south)

Storm motion: Northwest to southeast

Likely storm effects: Heavy rain, lightning, gusty winds

Possible storm effects: Damaging wind gusts, hail, brief tornado

Very small chance of: Large hail

Rainfall potential: Highly variable. Locally up to an inch or so in heaviest storms.

Discussion

Thursday morning, a warm front lifted northeast across the D.C. region. This will pave the way for mostly sunny skies in the afternoon, along with an increase in heat and humidity as a south wind picks up.


Surface forecast chart for mid-afternoon today showing warm front and cold front. NOAA.

Meanwhile, a cold front will sag slowly southeastward across Ohio, and then Pennsylvania. Ahead of that front, a squall line has moved out of Ohio and into West Virginia. The system has produced spotty reports of wind damage in the morning.


Approaching squall line crossing Appalachians late Thursday morning. (Weathertap.com)

In the upper atmosphere, strong winds have created wind shear (increase in wind speed with altitude) of around 45-50 mph. That wind shear is quite robust for late May, across the Mid Atlantic.

The question is whether the approaching squall line poses a direct threat to D.C. in the mid- to late-afternoon. Three out of three forecast models that explicitly resolve convective storms say this system will fizzle as it crosses the Appalachians.

Assuming this is the case, two of those three models redevelop portions of the convective line, once the impulse has moved east of the Blue Ridge in Maryland. One of these models, the hi-res NAM, is shown below. It suggests storm redevelopment as early as 3 p.m.


Intense convective line forecast to redevelop east of Blue Ridge during mid-afternoon Thursday, per the hi-resolution NAM model. (StormVistaWxModels.com)

One other model, the HRRR, has been a holdout against barely any storms late Thursday afternoon and evening.


In contrast to the hi-res NAM model, the HRRR foresees very little, if any, convective storms this afternoon and evening. StormVistaWxModels.com.

This leaves us in a tricky situation.

We know that the atmosphere will be primed for convective storms — plenty of instability is expected to develop, and the wind shear is very favorable for organized, intense and long-lived storms. Accordingly, the Storm Prediction Center has raised the threat level for severe storms to Enhanced Risk (level 3 out of 5) for most of central Maryland (including Baltimore). The District and Northern Virginia are in the next threat category which is lower (Slight Risk).


Risk of severe thunderstorms in the Washington region. (National Weather Service Storm Prediction Center)

While two of the models argue for at least scattered storms, one essentially predicts a bust. That model, the HRRR, has the greatest ability to resolve individual thunderstorms, but has proved to be somewhat “hit or miss” with regard to its skill on some days.

Arguing against widespread storm activity is the somewhat diffuse nature of the “trigger” or mechanism needed to help lift the air. The cold front will not cross into our area until Friday morning. The warm front will have lifted into far northeastern Maryland. This leaves the D.C. region reliant on localized triggering mechanisms such as the mountains to our west or an energetic-enough, remnant impulse (outflow boundary) generated by the weakening squall line approaching the region.

We are hedging about 60-40 that storms will trigger in the 3-6 p.m. time frame. Any storm that does develop will find itself in an environment conducive to reaching severe levels.

The most likely form will be one or more bowing storm clusters or short lines, moving quickly toward the east-southeast. There are reasonable prospects for scattered, severe wind gusts, along with small to moderate sized hail (up to quarter-size). An isolated tornado cannot be ruled out, given the significant “rotational energy” contained in the wind shear.

The delineation between “strong” (borderline for damage) vs. “severe” (likely causing damage) storms should increase in direction toward the north, across the D.C.-Baltimore metro corridor.

CWG will be monitoring conditions for any weather watches that get issued.

Expired updates

3:35 p.m. TORNADO WARNING for Columbia, Md. until 4 p.m.; Severe thunderstorm warning for immediate Washington area.

Radar indicates a possible tornado just west of Columbia moving toward Columbia itself. Seek shelter immediately if in this area in an interior room in the lowest level, away from windows.

Elsewhere, severe thunderstorm warnings are in effect for much of the immediate area, including the District, through around 4:15 p.m.

These storms are quite vigorous with extremely heavy rain, dangerous lightning, winds to 60 mph, and a few areas of small hail. Stay inside until they pass.

They are fast movers, advancing at around 40 mph, and should push east of the Beltway by 4:30 p.m.

3:30 p.m. — Severe thunderstorm warning expanded to cover all of Washington’s northern suburbs. All of Washington’s north and west suburbs under storm warnings.

In addition to the thunderstorm warnings in effect for Montgomery, Fairfax, and Prince William counties, a new warning has been added through Howard, northern Anne Arundel, and Northern Prince George’s County until 4 p.m.

The line of storms moving through the area has solidified and become intense. Very strong winds are indicated on radar along its leading edge from Columbia southwest to Chantilly.

3:15 p.m. — Severe thunderstorm warning added for northern Virginia

Almost all of Washington’s western suburbs are now under a severe thunderstorm warning as a new alert has just been posted for eastern Loudoun, central and western Fairfax, central and western Prince William, and central Fauquier counties, in effect until 3:45 p.m.

Storms with torrential rain, lightning and wind gusts up to 60 mph are pushing southeast at 35 mph.

They should hit the western part of the Beltway between 3:30 and 3:45 p.m. and then moving inside the Beltway and through the District between about 3:45 and 4:30 p.m.

3 p.m. — Severe thunderstorm for Montgomery County

As this line of storm heads east, much of Montgomery county is now under a severe thunderstorm warning until 3:30 p.m. This warning also includes northwest Howard, southeast Frederick and northeast Loudoun counties.

This storm contains very heavy rain and may produce wind gusts to 60 mph.

Storms still look to move inside the Beltway between 3:30 and 4 p.m.

2:35 p.m. — Severe thunderstorm warning for Washington’s far western suburbs, including northern Fauquier and Loudoun counties

Storms in northwest Virginia, approaching Washington’s far western suburbs, have intensified, prompting severe thunderstorm warnings. These warnings cover much of Loudoun and northern Fauquier counties, including Leesburg, until around 3 p.m. Wind gusts up to 60 mph and small hail are possible with these storms.

These storms continue trucking along at around 35 to 40 mph and should near the Beltway around 4 p.m.

2:15 p.m. — Storms cross Interstate 81; severe warnings between Hagerstown and Thurmont, Md. and around Frederick

Radar shows a line of thunderstorms from just east of Hagerstown, Md. south through Winchester and Strasburg in Va.

The most intense activity is in northern Maryland approaching Thurmont, which is under a severe thunderstorm warning until 2:30 p.m. A second severe thunderstorm warning is in effect to its south, including Frederick, Md. until 3 p.m.

These storms passing through northern Maryland may produce areas of damaging winds up to 60 mph in addition to heavy rain and lightning.

South and southwest of northern Maryland into northwest Virginia, these storms are not as intense, but still producing downpours, lightning and gusty winds.

The storms are moving quickly eastward, around 35 mph, and will approach Washington’s far western suburbs, including Loudoun and upper Montgomery counties, in the next hour.