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Updated forecast: Scattered storms this evening, but most intense activity has passed

Earlier storms brought down trees and wires around Frederick and other parts of northern Maryland

6 min

Radar courtesy MyRadar | © OpenStreetMap contributors

5:05 p.m. — Storms stretch from Baltimore to McLean, but are not severe (last update)

While the storms that tracked from Frederick, Md. to north of Baltimore were quite intense, bringing down trees and wires (and prompting severe thunderstorm and tornado warnings), the rest of the storm activity is generally subsevere.

Radar shows storms stretching from Baltimore through Silver Spring back to McLean and Chantilly. This activity is also pushing toward the east-northeast and should cross the northern half of the Beltway area over the next hour to 90 minutes. Brief downpours, lightning and gusty winds are possible. This activity should remain mostly subsevere, but we can’t rule out an additional isolated severe storm.

This will be our last update in the article. Stay tuned for our new PM Update article for a fresh look at the forecast through Tuesday, which will post around 6 p.m.

4:30 p.m. — Storm, stretching through eastern Loudoun and Montgomery counties, have weakened some

Radar shows storms from Laytonsville (in Montgomery County) through Ashburn and back toward The Plains (on the Loudoun-Fauquier county border). There are currently no severe thunderstorm warnings in effect, but the cell over Montgomery County has very heavy rain and frequent lightning. This activity continues to progress east-northeast and should be near the northern part of the Beltway starting just before 5 p.m. The trailing storms to the southwest will probably enter our southern suburbs between 5 and 6 p.m.

3:54 p.m. — Severe storm warning for eastern Loudoun, western Montgomery and northern Fairfax counties

Strong to severe storms have advanced to near Leesburg and are rapidly moving into the zone that includes Ashburn, Poolesville and, by around 4:30 p.m., the Interstate 270 corridor — from Rockville to Germantown. These storms have a history of bringing down some trees, so head inside if you’re in their path. They look to near the northern part of the Beltway by around 5 p.m. or a little before.

3:35 p.m. — Strong to severe storms from Frederick to Front Royal sweeping east-northesat

A pretty potent line of storms has pushed east of Interstate 81 and now stretches from Frederick to Front Royal, which are both under severe thunderstorm warnings. This activity — which has brought down trees and wires near Frederick — is advancing east-northward more quickly (around 35 mph) than anticipated earlier. It should arrive in northern Fauquier, eastern Loudoun and western Montgomery counties over the next 30 to 60 minutes. It may approach the Beltway by around 5 p.m., maybe even a little earlier.

Original article

It’s hot and muggy and a cold front is approaching the Washington area. Those are key ingredients for strong to severe thunderstorms that could produce very heavy rain and strong — even damaging — winds.

The National Weather Service has issued both severe thunderstorm and flood watches for the region into this evening.

Storms were already developing along and east of the Interstate 81 corridor mid-Monday afternoon and are projected to sweep across the Washington region in the late afternoon and early evening hours. Storms may reach the Route 15 corridor from Frederick to Warrenton by 3 or 4 p.m., the Beltway closer to 5 p.m., and Southern Maryland and the bay by 6 or 7 p.m.

The severe storm watch, which stretches from Northern Virginia to western Connecticut, affects 40 million people and expires at 10 p.m. “Thunderstorms will intensify this afternoon along a corridor from Northern Virginia into southeast New York,” the watch says. “The stronger cells will pose a risk of locally damaging wind gusts.”

Remember that a severe thunderstorm watch means conditions are favorable for intense storms, but not a guarantee. If a severe thunderstorm warning is issued for your location, on the other hand, it means a severe storm is imminent and you should seek shelter immediately.

Given the prospect of heavy downpours and how soggy it’s been over the last week or so, the Weather Service has also issued a flood watch until midnight.

“Afternoon to evening showers and thunderstorms may produce very heavy rainfall capable of flash flooding. This could include multiple rounds of storms which would enhance the flood risk,” the Weather Service writes. “Rainfall rates may reach 1 to 2 inches per hour, locally higher in spots. The D.C. and Baltimore metros will be the most susceptible given recent heavy rainfall the past couple of weeks.”

Remember, if you’re traveling late this evening, try to avoid routes that normally flood and, if you encounter high water, turn around, don’t drown. Places most susceptible to flooding include spots near creeks and streams as well as low-lying, poor drainage areas.

Also be aware that a few storms could be severe, with damaging gusts. Remember, “when thunder roars, go indoors.”

Severe storms with a damaging wind threats may tend to focus in areas north and northeast of Washington.

Even though the atmosphere has destabilized in advance of the cold front, and an approaching jet stream disturbance will increase uplift of air, the most intense wind shear and potential for widespread severe storms resides over Pennsylvania and New Jersey. Severe cells may be somewhat more isolated farther to the south.

The Washington region may be a little more prone to flooding given the exceptionally moist atmosphere overhead which will make for heavily raining storm cells. While these cells will be on the move, the very wet prevailing soils may present some patchy flooding concerns.

It’s been a very stormy stretch in the Washington region over the past two weeks. Multiple severe storm and flooding episodes have affected the area. Reagan National Airport has already picked up 6.57 inches of rain this month, the 21st wettest July on record with still nearly two weeks left.

The repeated storminess is tied to the fact that the jet stream, along which storms track, has consistent flowed through the Mid-Atlantic region. One silver lining of the jet stream pattern is that it has mostly kept away excessive heat.

Northeast enjoys blissfully mild summer as Plains and South bake