Severe storms cause numerous wind damage reports, especially in D.C.'s north and west suburbs

Numerous severe weather reports have come in across the area thus far. A map and sampling of them is below.

• Tree branches and power polls down east of Dulles Town Center
• Trees and wires down near Great Falls
• Multiple trees and wires down near Laytonsville
• Golf ball sized (1.75″) hail near Oakton
• Trees down on MD-117 near Germantown
• Large trees down near Dayton
• Power lines down on tree, causing a fire in Glenmont
• Multiple large trees down in Vienna
• Multiple trees down near Glenn Dale
• Large pine trees snapped near Boyds
• About 30,000 customers without power in the local region

6:25 p.m. update — Severe warning dropped in Washington, storms remain intense east and south

The severe storm warning for D.C. was dropped early as the main storm passes to the south. Heavy storms are lined up from Alexandria and to the south, with another batch of severe storms about to move into the bay from near Annapolis to Chesapeake Beach.

6:00 p.m. update — Another severe storm warning for D.C. and south, and the Annapolis area

Much of the local area is or recently has been under some sort of severe storm warning. The most recent was issued for Washington and areas to the south as storms crawl toward the city from the west. It runs until 6:45 pm. In addition, the Annapolis area is under a new warning. Both of these are for winds to 60 mph.

Original post below

A severe thunderstorm watch has been issued for the region. It runs until 8 p.m. Storms developing over the mountains to the west roll east through the area this afternoon into evening.

While the environment supports a pulse-type storm event, where storms go up and then fall apart just as quick, strong instability will aid the potential for powerful downdrafts as high as 60 mph or so. Wind damage is possible in the strongest activity.

For most spots, the main risks will be frequent lightning plus heavy and potentially flooding rain. Given the hit-or-miss nature, some locations may not see much.

Timing for main line:

• Interstate 81 (Hagerstown/Winchester/Front Royal): 2-4 p.m.
• Route 15 (Frederick/Leesburg/Gainesville): 3-5 p.m.
• Interstate 95 (Baltimore/Washington/Fredericksburg): 4-6 p.m.
• Route 301 (Crofton/Upper Marlboro/Waldorf): 5-7 p.m.

A few storms could develop before the main broken line passes through.

Storm motion and duration: Moving west to east and lasting 1 hour or so.

Main threats: Heavy rain, lightning, localized damaging wind gusts.

Small chance of: Hail.

Rainfall potential: Highly variable. Up to an inch or two in the heaviest storms. Many spots see little rain.

All clear: By 8-10 p.m.

Confidence: Medium-High. Coverage of storms is uncertain, but scattered activity is likely.

Discussion

The thunderstorm potential this afternoon and evening continues the general trend of the past week. On most days we have seen a very unstable (hot and humid) air mass, and weak winds aloft. Given those weak steering winds, storms are presently erupting over the mountains and drifting very slowly toward the east-northeast.

Without strong winds aloft (and therefore very weak wind shear), we do not expect storms to organize into a long-lived and widespread line, nor supercells. But the intensely unstable atmosphere should make up for the lack of shear, causing some cells to pulse — that is, briefly reach severe limits over localized areas, before dissipating.

When the heavy rain cores of these cells collapse, microbursts can develop and create damaging gusts near or past 60 mph in some locations. Additionally, torrential downpours and vigorous lightning are a good bet with any of these storms. There is also the chance of localized flash flooding, given very slow movement of storm cells.

We expect the mode to be largely hit-or-miss through the later afternoon and evening, with activity waning as the sun goes down. Thunderstorm downdrafts may merge together in spots (creating larger pools of chilled air) that in turn may organize small cells into larger, more persistent clusters.

Prior updates

5:50 p.m. update — Damage reports in the local area as storms continue to rage

Some more local storm reports are coming in (moved up to top). NWS is also highlighting the potential for 70 mph winds around Reston, Herndon, and Vienna.

5:17 p.m. update — Severe storm warning for D.C. and surrounds until 6 p.m.

A severe thunderstorm warning has been issued for the city and surrounding areas until 6 p.m. Wind gusts of 60 mph are possible with this storm. Although it’s been dry with distant thunder so far in the city, it’s a good time to plan on being indoors and away from windows.

4:50 p.m. update — Severe storm warning for western parts of the immediate area

A new warning is up for areas west of the city, including Herndon, Vienna, and McLean. It runs until 5:15 p.m. and the warning is primarily for damaging wind threats. Some spots of strong wind have been noted near Great Falls and Dayton, Md. recently.

4:45 p.m. update — Major gusts in some spots as storms go up and collapse on themselves

These storms are going up, not moving much, then collapsing, in general. You can see a recent signature of a downburst near Damascus, where severe winds and wires have been reported downed. While many spots won’t see severe winds, some are seeing very intense gusts.

4:30 p.m. update — Storms focused on northern suburbs, some very strong winds

A severe thunderstorm warning for a big chunk of the northern suburbs has been issued until 5:15 p.m. This storm is warned for winds up to 70 mph. A gust of 58 mph was recorded on a mesonet station near Germantown. Additional storms to the south, near Warrenton, are also warned, with one producing a wind gust of 74 mph at Warrenton Airport in Fauquier County.

4:05 p.m. update — Another local warning, parts of Loudoun, Fairfax and Montgomery counties

A severe storm warning has been issued surrounding the earlier one locally, s storms expand without moving too much. It runs until 4:45 p.m., for the risk of damaging wind and quarter sized hail.

3:50 p.m. update — Severe thunderstorms popping locally

A severe thunderstorm warning has been issued for parts of Montgomery County, including Seneca, North Potomac, and Rockville until 4:30 p.m. Wind gusts of 60 mph are possible along with quarter sized hail.

Several reports of trees and wires down have come in from near Frederick.

3:40 p.m. update — Storms firing locally, and severe storm near Frederick

A severe thunderstorm warning is up for Frederick County until 4:15 p.m. Wind gusts of 60 mph are possible.

Additionally, storms have begun to fire up locally, in the Potomac, Md., area and to the east of Sterling. Given the high heat and humidity, these storms could become intense as well.