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Storm updates: Flash flood warning for District

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* Flood watch until 11 pm *

5:05 pm — Flash flood warning for District with intense storms to the east

Torrential rain has produced 1.5 to 2.5 inches inside some parts of the city and another inch or so is possible. “Flash flooding is ongoing or expected to begin shortly,” writes the National Weather Service.

It would be best to delay commuting for another hour or so when the rain should be letting up.

If you have to travel and encounter standing water in your vehicle, turn around, don’t drown.

The most intense storm activity is now east of the District, prompting a severe thunderstorm warning from around College Park to Annapolis until 6 pm

Our next update will be around 5:30 pm

4:55 pm — Heavy storms soaking entire region; flooding in spots

Storms with heavy rain cover the entire Beltway area and locations to the north, south and southwest. Radar estimates of wind speeds aren’t that strong, but these storms are major rain and lightning producers.

Over two inches of rain have fallen near Oakton, Alexandria and between Dale City and Bristow where flash flood warnings are in effect for the next two to three hours. A few places could see totals up to 4 inches before the worst of the rain moves off after around 6 pm

4:30 pm — Storms with heavy rain continue to increase west of Washington as they push inside the Beltway

Radar shows widespread storms north and west of downtown Washington with some of the heaviest downpours in Fairfax County where severe thunderstorm warnings have been issued through 5 pm in both the northern and east central parts of the county.

Another severe thunderstorm warning covers northwest Washington and southern Montgomery County until 5:15 pm Localized gusty winds are possible in all of these locations although the primary threats are torrential rain and dangerous lightning.

Additionally, there is a flash flood warning for the area west of Dale City until 7:30 pm where 1.5 to 2.5 inches of rain has fallen and an inch or so is possible.

In short, it’s very stormy west of Interstate 95 and all of this is pointed at the I-95 corridor and areas to the east over the next one to two hours.

3:50 pm — Storms becoming numerous west of Beltway

Radar shows storms popping up throughout the region but there is more of a solid line in western Loudoun County extending southwestward toward Front Royal. The storms, headed eastward at around 15 mph, contain heavy downpours and frequent lightning. There are no severe thunderstorm or flash flood warnings at the moment, but that could change at any time.

Inside the Beltway, we have a few isolated downpours scattered around and it may take until between 5 and 6 pm for the more solid line of storms to reach the area.

Original article from 1:15 pm

Since August began, the Washington region has felt like a steam bath, culminating in Tuesday’s oppressive high of 97 degrees. But our 10-day run of sweaty weather is about to end.

Seldom does the air mass change from hot and muggy to dry and comfortable without thunderstorms. And numerous storms are expected this afternoon and early evening; some could be quite heavy.

The National Weather Service has issued a flood watch from 2 pm to 11 pm in anticipation of the downpours.

“Showers and numerous thunderstorms are expected this afternoon into this evening,” the Weather Service says. “Rainfall amounts will average around 1 to 1.5 inches across the area, but locally higher amounts of 2 to 4 inches are likely and much of that may fall in a one to two hour time frame.”

Areas most vulnerable to flooding include those near creeks, streams and zones where there is poor drainage. July and the beginning of August have been wetter than normal in most parts of the region, which increases the potential for flooding since the soils are already wet.

In addition to the heavy rain, storms will also bring dangerous lightning and very strong localized wind gusts. The Weather Service has placed our area in a marginally elevated risk zone for severe storms because of gusts that could cause tree damage.

Why there aren’t National Weather Service warnings for lightning

Short-term models project numerous storms in our western areas between 3 pm and 5 pm, close to the Beltway between 4 pm and 6 pm and into our eastern suburbs between 5 pm and 7 pm However, more isolated storms could develop early this afternoon ( especially west of Washington) and linger past sunset (especially south and east of Washington).

The forecast weather map for early evening (shown below) depicts the very slow-moving front (and in fact, additional fronts to approach from the Northwest later tomorrow). The slow-moving front is expected to focus heavy rain and thunderstorm development across the greater DC region starting as early as midafternoon today, and continuing into the evening.

The mountain terrain to our west and bay breeze circulations to our east will add to a focused uplift of a moist, unstable air mass. A weak high-altitude disturbance is also approaching and will boost the uplift more broadly.

The first widespread threat is for torrential rain that may lead to flash flooding. The atmosphere is exceptionally moist through a deep level, and storm cells will move slowly — given very weak flow aloft. Additionally, those weak winds are aligned parallel to the frontal boundary — creating an ideal setup for repeated passage or “training” of cells over the same regions.

A second, more marginal threat will be for a few storms to reach severe levels, in terms of isolated wind gusts reaching or exceeding 55-60 mph. These so-called “microbursts” can occur when the heavy, wet cores of storm cells collapse — creating a chilled outburst of violent wind at the ground.

Multi-fatality lightning strikes are rare, but most have this in common

As always, it’s worth reminding folks to be lightning aware. The sobering loss of life from severe storms last week near the White House is a reminder that all it takes is one strike. We’ve had an especially stormy summer and in our densely-populated region, everyone should be mindful not to neglect lightning as a distinct storm hazard.

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