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Update: Flash flood warnings for areas north of downtown Washington

4 to 7 inches of rain estimated in parts of southern Montgomery County with flooding and water rescues reported


Radar courtesy MyRadar | © OpenStreetMap contributors

12:35 a.m. -- Southern Montgomery County hammered by heavy rain and flooding

The heavy rain should let up soon, but for the moment continues across southern Montgomery County, the northern tip of D.C., and areas east of the Beltway. Parts of Rockville and Silver Spring have seen an estimated 4 to 7 inches of rain with another 0.5 to 1 inches or so possible around Bethesda, Silver Spring, Takoma Park and College Park. See below for a sampling of numerous reports of flooding and some water rescues.

11:15 p.m. — Yet another flash flood warning in Montgomery County; 3 to 5 inches of rain and counting

Kind of weird, but we have a flash flood warning inside of another flash flood warning in central Montgomery County including Rockville, Derwood and North Potomac. Radar-estimated rainfall is already 3 to 5 inches in this inner flash flood warning, which is in effect until 1 a.m., with more to come during the next couple of hours.

Note that the flash flood warning for northern D.C. and nearby areas mainly inside the Beltway--including McLean, Bethesda, Silver Spring, College Park and Takoma Park--has been extended until 3 a.m. as rain heavy rain continues to train across this area.

10:40 p.m. — Another flash flood warning issued, this time for lower Montgomery County

A new flash flood warning is in effect until 1:30 a.m. for lower Montgomery County including Travilah, Potomac, Derwood, Rockville, Wheaton, Aspen Hill and Colesville. While currently it is only raining in the northern half of this flash flood warning zone, another area of storminess now moving through the Leesburg area could target the entire warning area in the next couple of hours as it moves east.

9:10 p.m. — Flash flood warning from McLean through northwest Washington to Beltsville until midnight

While storms were slow to develop this evening, they have increased dramatically in coverage and intensity especially in areas north of downtown Washington. Heavy storm cells, passing over the same areas repeatedly, has prompted a flash flood warning from northeast Fairfax County through northwest Washington into southern Montgomery County until midnight.

“Between 2 and 3 inches of rain have fallen,” the National Weather Service writes. “Additional rainfall amounts of 1 to 2 inches are possible in the warned area. Flash flooding is ongoing or expected to begin shortly.”

Best to avoid traveling in this zone until this rain subsides. Remember to never attempt to drive across a flooded road. Turn around, don’t drown.

Based on radar trends, conditions should improve between 10 and 11 p.m. in this flash flood warning zone.

Aside from this complex of heavy storms triggering the flood warning, just one other storm caused issues earlier this evening. Between 7 and 8 p.m., a severe storm passing between Potomac and Rockville unleashed strong winds which brought down trees, including one on a home:

Original forecast

Both severe thunderstorm and flood watches are in effect in a region stretching from Virginia to New Jersey through this evening due to the likelihood of storms, especially between about 5 and 10 p.m. The main three hazards with any storms will be torrential rain, lightning and some damaging wind gusts.

Remember that a severe thunderstorm watch means ingredients are in place for intense storms but may or may not come together. However, if a severe thunderstorm warning is issued for your location, it means an intense storm is imminent and you should seek shelter.

As of late this afternoon, a few storms have already popped up along the Interstate 64 and Interstate 81 corridors, but there are no imminent storms in the immediate metro region. Strong to severe storms are most probable during the evening hours — especially toward sunset.

Calmer weather will move in Sunday, with rain chances diminishing quickly in the morning, and then clearing skies during the afternoon.

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Through tonight: Thunderstorms may slowly close in on the region through the evening hours. The main threats are damaging wind gusts in some storms. Secondarily, we have the threat of flooding downpours and lighting. At least a half inch of rain is possible for many of us, but a quick one or two inches of rain inside the heaviest of thunderstorms can’t be ruled out.

Additional showers or lesser thunderstorms are possible later into the night as temperatures bottom out in the upper 60s and low 70s. We’ll monitor the rain amounts late night to make sure they don’t exacerbate flooding issues from earlier storms.

View the current weather at The Washington Post.

Tomorrow (Sunday): Final showers will move out of the region in the morning, as light southwest breezes turn toward the northwest, indicating that the cold front has passed. Southern Maryland may be the last place in the region to clear its showers, perhaps midday.

After showers end, we all have a couple more hours of clouds behind them but afternoon skies will be bluer. High temperatures may range from 83 to 88 degrees, and humidity levels will slowly head downward.

See Ian Livingston’s forecast through the weekend. And if you haven’t already, join us on Facebook and follow us on Twitter and Instagram. For related traffic news, check out Gridlock.

Tonight’s strong to severe storm time frame

Tonight the area around the Beltway should most keep an eye on the 6 to 9 p.m. window. That is when storms may most target the D.C. area and Interstate 95 corridor. A few storms could linger after that, but the potential for damaging wind gusts should diminish a bit before the flooding downpour threat.

Small hail and frequent lightning are also a possibility this evening, even after the strongest of storms die down somewhat after 9 or 10 p.m. Always keep in mind “when thunder roars, head indoors” — if you hear thunder, lightning is close enough to strike.

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