The Washington PostDemocracy Dies in Darkness

Second round of storms passing south of Beltway after first wave causes damage to the north

Concern through the evening will be possibility of flooding south of Washington after earlier storms brought damaging winds and hail. Power outages topped 180,000.


Radar courtesy MyRadar | © OpenStreetMap contributors

9:20 p.m. — Storms from Culpeper to Southern Maryland; stunning sunset in immediate D.C. area

Storms are lined up like train cars from Culpeper to Southern Maryland where several severe thunderstorm warnings are in effect and flooding is also a concern for the next couple of hours.

To the north — near the immediate D.C. area — the heaviest storm activity ended long ago but there are still some thundershowers in the area and lightning. The combination of the storm clouds. lightning and the setting sun made for a spectacular sunset.

Phenomenal sunset boasts red sky, lightning and rainbows — all at once

Here’s the forecast for the rest of tonight into tomorrow:

The severe weather threat has waned in the immediate area, but showers and storms may continue for a few hours after sunset, lingering longest near the bay and in southern Maryland. Any storms traveling over the same area repeatedly could lead to flooding. Lows are in the upper 60s and lower 70s. Winds blow from the west and southwest around five mph.

Skies are partly to mostly sunny and humidity is down somewhat from Tuesday. You’ll still feel it, but not quite as much. High temperatures should rise to within a few degrees of 90. Winds are out of the northwest and west around five to 10 mph. We’ll probably stay dry, but an isolated shower or storm isn’t impossible in the afternoon.

Tomorrow, we’ll have a recap of the violent bow echo that traversed the region and caused significant damage around Olney, with downed trees on homes displacing dozens of families according to Pete Piringer of the Montgomery County Fire and Rescue:

7:00 p.m. — Severe storms exit with 180,000 power outages in Maryland and Virginia; watching flood risk due to new wave

The initial, intense line of storms is mostly through the region now. However, in its wake, there are some issues:

  • According to PowerOutage.US, there are about 180,000 power outages in Maryland and Virginia. Most of the outages are in northern Maryland from Carroll County to Cecil County, but there are over 20,000 outages in Prince George’s County and 10,000 in Montgomery County. About 35,000 outages are scattered through Northern Virginia, about half of them in Fairfax County.
  • The strong winds toppled numerous trees in the region. Hardest hit appears to be Olney, where a probable microburst caused heavy tree damage. Tree damage was also reported near College Park, Bowie, Centreville and Chantilly.
  • Among other storm observations, Dulles Airport clocked a 61 mph gust and Reagan National Airport reported hail. A wind gust of 70 mph was reported near Centreville.

While the threat of storms with damaging winds in the immediate area has lessened, the National Weather Service issued a bulletin about the flooding potential due to a second wave mainly focused south of the District. A zone of west-to-east oriented storms has set up just south of the Beltway where some areas could see storm cells pass over repeatedly or train, presenting a flood risk.

“An axis 2-4” [rainfall] totals are possible likely from Rockingham, VA toward Prince William and across into Charles county this evening," the Weather Service wrote. We will update if flooding materializes.

Below, find some images of the earlier storminess:

6:30 p.m. — Intense storms from Odenton to Bowie to Upper Marlboro pointed toward Annapolis

The bow-shaped severe storm complex is sweeping through areas east of the District with the most intense activity near the apex of the bow east of Bowie. Torrential wind, hail and localized bursts of damaging winds are probable. The whole complex will sweep through Anne Arundel and northern Calvert County before exiting over the Bay around 7 p.m.

6:10 p.m. — Severe storms from Laurel to Alexandria sweeping into D.C.'s eastern suburbs; intense burst of winds east of College Park

Radar shows the intense bow-shaped line of storm pushing east of Interstate 95 with the most intense activity between College Park and Greenbelt where there are probably damaging wind gusts (of 60-70+ mph). Severe thunderstorm warnings are in effect for most areas east of the District through 6:45 or 7 p.m.

5:40 p.m. — Wind gusts could reach 70 mph in dangerous storms approaching Beltway; severe thunderstorm warning for much of the immediate area

A bowing complex of intense storms stretches from Germantown to Oakton to Centreville to Gainesville. The storms have a history of producing hail and wind gusts over 60 mph. Dulles Airport gusted to 61 mph around 5:30 p.m. Wind gusts could reach 60 to 70 mph as the storms pass through central Fairfax County between Oakton and Fairfax and possibly toward Annandale and Falls Church.

The National Weather Service has extended the severe thunderstorm warning, now in effect until 6:15 p.m., for much of the Beltway area including the District.

5:15 p.m. — Severe thunderstorm warning for most of D.C.'s immediate western suburbs until 5:45 p.m.

The line of severe storms — currently stretching from Leesburg to The Plains — is bearing down in eastern Loudoun, Fairfax, northern Prince William and southern Montgomery counties. As these storms sweep eastward, they’ll produce torrential rain, small hail, lightning and widespread wind gusts of 30 to 50 mph. Localized wind bursts, which could cause tree damage, could top 50 to 60 mph.

This line of storms should reach the western edge of the Beltway around 5:45 p.m. and move inside the District before 6 p.m. Stay inside and off the roads while these pass.

4:45 p.m. — Intense storms heading into Loudoun County — could be near Beltway before 6 p.m.

Radar shows a very intense storm — probably containing damaging winds — entering southwest Loudoun and northwest Fauquier counties, prompting a severe thunderstorm warning until 5:15 p.m. This storm will pass through Purcellville, Middleburg, and The Plains over the next 30 minutes and will probably reach Ashburn and Haymarket by around 5:15 p.m. As the storm is moving swiftly eastward at around 50 mph, it could near the Beltway a little before 6 p.m.

2:55 p.m. — Severe thunderstorm watch in effect until 10 p.m.

As thunderstorms have begun to organize in western Maryland and northern West Virginia, the National Weather Service has issued a severe thunderstorm watch for the Washington region until 10 p.m. tonight.

“Thunderstorms will increase in coverage and intensity through the afternoon/evening while spreading eastward from West Virginia across northern Virginia and Maryland,” the watch states. “The storm environment will favor clusters and line segments capable of producing damaging winds up to 70 mph, as well as isolated large hail near 1 inch diameter.”

The D.C.-area severe thunderstorm watch is one of three extending from Central Virginia to Vermont.

Remember that a watch means conditions are conducive for the formation of intense storms, but that they are not a guarantee. Stay alert. But if a severe storm warning is issued for your location, it means a severe storm is imminent and you should seek shelter immediately.

We will post updates as storms develop and move through the area at the top of this article.

Original article from 1:30 p.m.

After a delightful day with below-average temperatures and humidity Monday, steamy air has surged back into the area. As a cold front clashes with the hot, muggy air in place, strong to severe thunderstorms could erupt across the Washington region, especially this evening.

Computer models suggest the most probable window for storms is between about 6 p.m. and midnight.

“Damaging downdraft winds will become a concern as thunderstorms gradually increase in coverage and intensity. Some severe hail may also occur,” the National Weather Service wrote in a special bulletin about the storm threat. The bulletin said that a severe thunderstorm watch will probably be issued.

The Weather Service has placed the region in a Level 3 out of 5 “enhanced” risk zone for severe storms.

A flood watch has already been issued for the region.

“Strong to severe thunderstorms will move across the region late this afternoon through the evening hours,” the National Weather Service wrote in the flood watch statement. “Heavy rain will accompany a number of these storms which may drop 1 to 2 inches of rainfall in an hour. Additionally, some regions could see repeat thunderstorm activity leading to an enhanced threat for flooding.”

Areas most prone to flooding include those near creeks and streams as well as low-lying, poor-drainage areas. At additional risk are those areas that were deluged last week with over 4 inches of rain, including parts of Fairfax, Montgomery and Prince George’s counties as well as the District. In these areas, the ground is already somewhat saturated, and stream levels are high.

Storm threat at a glance

Timing: Storms are most probable in the 6 p.m. to midnight window, but a few isolated cells could pop up late this afternoon. Here’s when the majority of storms might first arrive:

  • Interstate 81 (Hagerstown to Front Royal): 4 to 6:30 p.m.
  • Route 15 (Frederick to Warrenton): 5:30 to 7:30 p.m.
  • Interstate 95 (Baltimore to D.C. to Fredericksburg): 6:30 to 8:30 p.m.
  • Route 301 (Bowie to La Plata): 7 to 9:30 p.m.

Some areas could see more than one round of storms.

Hazards:

  • Likely: Very heavy rain, gusty winds (30 to 50 mph)
  • Possible: Flooding, damaging winds (50 to 70+ mph), small hail
  • Small chance: Large hail, isolated tornado

Discussion

The severe-weather story today focuses on several potential hazards — severe storm activity and the potential for flash flooding late Tuesday afternoon and into the evening.

Let’s start with the forecast weather map for early evening (shown below). A cold front associated with a dip or trough in the jet stream will arrive on our doorstep by early evening. Ahead of the front, “return flow” around the western flank of the Bermuda High — from the south-southwest — will combine with abundant sun to raise surface temperatures and dew points, a measure of humidity, into the low 90s and low 70s, respectively. Any time the dew point is over 70, it’s oppressively humid.

Meanwhile, a belt of strong winds in the middle atmosphere will approach from the west, as the trough moves out of the Great Lakes. Both the trough and region of enhanced wind are shown in the late-afternoon forecast chart at 18,000 feet (below).

It’s a solid setup for scattered to widespread intense thunderstorms. The hot, humid air mass at low levels and cooling of atmosphere in upper levels (due to the approaching trough) will cause significant destabilization of the atmosphere. The belt of strong westerly flow aloft will increase the shear, or changing of wind direction and speed with altitude. Wind shear increases the intensity of storm cells and promotes better organized, longer-lived storm complexes.

One of the factors to note are a few stable layers in the atmosphere. Certain layers are unstable and will become more unstable with continued heating and moistening of the surface. But the morning weather balloon launch at Washington Dulles International Airport indicated a few shallow but significant regions of atmosphere that could rob storm updrafts of buoyancy, and mitigate the severity of storms a bit. It’s also possible that these intervening layers will “mix out” by evening and the entire, deep atmosphere will be fully primed to maintain strong updrafts. This factor will be hard to assess unless the Weather Service launches a special midafternoon sounding balloon.

The morning model runs are unanimous about generating widespread storms along the front, starting in the late afternoon. The cells will quickly come together into better organized multicellular complexes. Some of these complexes may take on a fast-moving, bowing configuration; a few may develop transient supercell-like characteristics, meaning that they are rotating.

Scattered instances of damaging winds are the greatest single storm threat, with gusts over 60 mph possible. Some instances of hail are possible, and a brief tornado could initiate from a weak supercell or two.

There is also indication that waves of storms could move repeatedly over the same regions as we get into evening. This “training” potential is the reason the Weather Service has issued a flood watch across the region.

CWG meteorologists will be monitoring and updating the forecast as we move through the day.

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