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Capital Weather Gang

Torrential rain triggers widespread flooding in D.C. area, inundating roads, stranding motorists

Up to 6 inches of rain fell. Drier air arrives Friday into Saturday,

By
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September 10, 2020 at 5:17 p.m. EDT

Radar courtesy MyRadar | © OpenStreetMap contributors

* Flash flood watch through this evening *

Overview: A narrow corridor of extremely heavy rain developed over the immediate Washington region mid-Thursday afternoon, resulting in widespread flash flooding. Streams rose up to 8 feet in a single hour, and some roads were engulfed in floodwaters and closed. Dozens of cars were stranded in high water and required rescue. The heaviest rain, totaling 2 to 6 inches, focused in southern Montgomery County and between Alexandria and north-central Prince George’s County, including the northeast portion of the District. Washington received 2.88 inches of rain from the deluge, a record for Sept. 10. The rain eased by late afternoon.

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Record-setting rain deluges Washington, submerging roads and stranding drivers

Extremely heavy rain triggered widespread flooding in the immediate Washington region on Sept. 10. (Video: The Washington Post, Photo: Matt McClain/The Washington Post)

5:15 p.m. — Weather Service logged 40 reports of flooding from Alexandria to Aspen Hill

The National Weather Service map of flood reports shows the extent of today’s flooding. Reports were most numerous in Alexandria, the northeast part of the District, southern Montgomery County, and northwest Prince George’s County. These reports documented scores of high-water rescues, flooded roads, and creeks streams surpassing flood stage.

We’ll have a detailed report Friday describing how this event happened and summarizing rainfall amounts. For the forecast for the rest of this evening into tomorrow, see our PM Forecast update.

4:55 p.m. — Tremendous flooding along Route 50 in Maryland

A photo from WTOP traffic reporter Dave Dildine shows Route 50 engulfed in floodwaters at the intersection with Kenilworth Road in Maryland, inside the Beltway. Water rescues are reportedly ongoing.

4:15 p.m. — Worst of rain exits hardest-hit regions; flash flood warning in Southern Maryland

Radar shows that heavy rain has moved out of the areas in the immediate metro region under flood warnings but that high water lingers near creeks and streams. Occasional showers are still possible into the evening, but torrential rainfall is not predicted.

The heaviest rain is located in Southern Maryland, which is under a flash flood warning, and areas adjacent to the Chesapeake Bay.

4:05 p.m. — Heaviest rainfall totals exceeded 6 inches in Hyattsville, Md.

A National Weather Service rainfall analysis shows that a pocket of heavy rainfall in northeast Washington and northwest Prince George’s County produced totals of 4 to 6 inches, within a broader area of 1 to 3 inches from Alexandria to the north and northeast through the District and southern Montgomery County.

4 p.m. — Floodwaters force motorists to abandon cars along Rock Creek

Driving near creeks and streams should be avoided until waters recede (and flood warnings expire). This scene from Rock Creek Park shows why:

3:40 p.m. — Radar indicates rainfall totals of up to 4 inches, heaviest between northeast D.C. and College Park

3:25 p.m. — Flash flood warning extended until 6:45 p.m. in southern Montgomery County

While torrential rain has exited southern Montgomery County, many streams are above flood stage and adjacent roads are flooded, requiring the flash flood warning to be extended until 6:45 p.m.

3:15 p.m. — Heaviest rain along east branch of Beltway and along Interstate 95 north of Beltway

Radar shows the heaviest rain now generally north of downtown Washington between Takoma Park and Columbia and extending to the east and southeast from roughly Beltsville to Camp Springs. This rain is headed north up the Interstate 95 corridor into Howard, Anne Arundel and Baltimore counties and is likely to cause areas of flooding.

In the past hour, the Weather Service has logged reports of flooding between Alexandria and northern Prince George’s County, including the northeast section of the District. Prince George’s County Fire and Rescue reported multiple water rescues in Hyattsville, Mount Rainer and Brentwood. At 2:50 p.m., multiple vehicles were reported stranded on the George Washington Parkway near Reagan National Airport in Alexandria.

Here are some more images of flooding:

2:45 p.m. — Flash flood warnings expanded into central Prince George’s County

2:40 p.m. — Streams are rising very rapidly

As torrential rain continues, mainly north and northeast of downtown Washington, the National Weather Service has logged some rapid rises in water in area streams:

  • Stream gauge on Turkey Branch in Rockville rose 7 feet in just over an hour.
  • Stream gauge on Sligo Creek in Takoma Park rose 4 feet in an hour.
  • Stream gauge on the northwestern branch of Anacostia River at Colesville rose 8 feet in an hour.
  • 3 to 4 feet of water is covering Beach Drive at Connecticut Avenue from flooded Rock Creek.

2:30 p.m. — Radar shows large areas of 1.5 to 3 inches of rain

As shown in the image below, the heaviest rain has focused between Bethesda and Aspen Hill in Montgomery County and from Alexandria through northeast parts of the District:

2:10 p.m. — Torrential rain in the eastern half of District, where flooding is increasing

In hard-hit areas of southern Montgomery County around Bethesda and Kensington, which flooded earlier, the heaviest rain has eased. But now torrential rain is focused in D.C., especially in areas downtown and to the east; western Prince George’s County; and extreme-southeast Montgomery County.

The National Weather Service received a report of 6 to 8 inches of water flowing down Fourth Street in Northeast D.C., and there have been reports of vehicles stranded in high water.

Here are some images of the flooding:

1:55 p.m. — Several reports of cars stranded in high water in Montgomery County

The National Weather Service has received several reports of cars stranded in high water in Montgomery County, including:

  • A vehicle trapped on Dorset Avenue near Little Falls Parkway.
  • Three vehicles stranded near Kensington Parkway and Beach Drive.
  • A vehicle stranded in high water near Beach Drive and Wexford Drive in Kensington.
  • A vehicle trapped in high water near Colfax Street and Parkwood Drive in Kensington.
  • A vehicle trapped near Greentree Road and Md. 187/Old Georgetown Road in Bethesda.
  • Two vehicles trapped in high water near Arlington Road and Bradley Boulevard in Bethesda.
  • Vehicle trapped in near 6000 block of Alleghany Avenue in Takoma Park.

Bethesda Beat reported that Montgomery County Fire and Rescue had received 50 emergency calls.

“There’s been dozens of cars in water,” spokesman Pete Piringer told Bethesda Beat.

Do not attempt to drive through a flooded road in your vehicle. Turn around.

1:35 p.m. — Flash flood warning for eastern Fairfax County, the District and western Prince George’s County

As a narrow corridor of heavy rainfall focuses on the immediate area, with downpours lined up one after another, a flash flood warning has been issued for eastern Fairfax County, D.C. and western Prince George’s County until 4:30 p.m., in addition to the warning issued earlier for southern Montgomery County.

In this new flash flood warning zone, around 0.5 to 1.5 inches of rain has fallen and another one to two inches is possible.

In general, 2 to 3 inches of rain could fall in areas where heavy downpours pass repeatedly, with some locally higher amounts not out of the question.

1:30 p.m. — Images of flooding from Montgomery County

12:50 p.m. — Flash flood warning for southern Montgomery County

A flash flood warning has been issued until 3:45 p.m. for much of southern Montgomery County and a small part of northwest D.C. Radar shows very heavy rainfall between Bethesda and Olney. Around an inch has fallen in some areas, and another inch or so could fall in the next hour.

“Flash flooding is ongoing or expected to begin shortly,” the National Weather Service warned. Small creeks and poor-drainage areas are most vulnerable to flooding. Do not attempt to drive across a flooded road, where the depth of the water may be deceptive.

12:15 p.m. — Showers have increased and some could be heavy this afternoon

Today’s forecast is a bit of a moving target as showers have increased across the region, cycling in and out from southeast to northwest. There are breaks between the showers, but also some embedded heavier downpours. Radar shows more showers developing southeast of the region, which could be heavy in spots as they streak northwest through the afternoon.

The truth about the weather today may fall in the middle of our earlier forecasts — not as wet as our initial forecast issued at 5 a.m. but wetter than the 10 a.m. update signaled.

10 a.m. — Not as rainy today as previously anticipated

Radar and short-term models do not indicate as much rain as we were previously expecting today. Since this morning, the heaviest rain has focused east and southeast of the Beltway, and it has now exited the region.

The atmosphere is still very humid, and pop-up showers could still occur at any time, but it will be dry more often than not.

A few showers later today could be heavy, especially this afternoon and evening. But we no longer expect widespread rainfall of 1 to 3 inches, and some areas could end up with very little. Below is the updated rainfall forecast from the National Weather Service for the period between 8 this morning and 8 a.m. Friday. We think this forecast is overdone, but, given the nature of summertime downpours, it’s not out of the question that a few locations will see amounts this high or even a bit higher.

The most widespread heavy rainfall probably occurred last night, during which a number of areas picked up 1 to 4 inches. Heavy amounts focused in Fairfax County, Southern Maryland and locations out toward the Blue Ridge. The National Weather Service supplied a list of totals. At the airports, Reagan National picked up 0.56 inches, Dulles 0.76 inches and BWI Marshall just 0.18 inches (through 9 a.m.).

Today’s daily digit

A somewhat subjective rating of the day’s weather, on a scale of 0 to 10.

3/10: With a surge of rain and humidity, you may choose to vent without timidity.

Express forecast

  • Today: Showers with locally heavy downpours, humid. Highs: 80-84.
  • Tonight: Showers gradually taper off, calm and humid. Lows: 67-73.
  • Tomorrow: Isolated shower early? Then increasing sunshine, lower humidity. Highs: 79-83.

Forecast in detail

Considering the raging fires and smoke in the West, it’s hard to complain too much about high humidity and downpours here today. That said, some pockets of flooding could occur, especially near small streams and in poor drainage areas. Conditions improve considerably Friday into Saturday before humidity and shower chances increase again Sunday.

Get our daily forecasts on your Amazon Alexa device.

Today (Thursday): Showers are possible anytime, and localized heavy downpours are likely, especially in the afternoon and the evening. But the sky may brighten at times as high temperatures reach for the low 80s. Humidity is oppressive with dew points in the mid-70s, while negligible breezes from the northeast offer little relief. Rainfall amounts are highly variable, but up to one to three inches could fall or even a little more, especially east of the city. Confidence: medium-high.

Tonight: Showers will remain a likely feature well into the night, and a few could be heavy. Humidity will remain on the high side with calm winds. Lows will be in the upper 60s to low 70s. Confidence: medium-high.

Follow us on Facebook, Twitter and Instagram for the latest weather updates. Keep reading for the forecast through the weekend …

Tomorrow (Friday): A fairly weak cool front will do its best to clear most showers out in the morning and start to lower humidity levels by the afternoon. Clouds will break up enough for some occasional sunshine as well. Breezes will be light from the north, and highs will top out in the upper 70s to low 80s. Confidence: medium-high.

Tomorrow night: Lower humidity and calming winds will allow temperatures to drop off nicely despite partly cloudy skies. Lows will bottom out in the low to mid-60s. Confidence: medium-high.

A look ahead

High pressure does a fairly good job of holding off showers and humidity on Saturday. By afternoon, clouds will build and a shower could pop up, but most activity should stay well to our south. Highs in the mid-70s will be a treat. Clouds will gather overnight, but showers be sparse. Lows will hold in the mid- to upper 60s. Confidence: medium.

Showers and humidity will surge back into the area on Sunday ahead of an approaching cold front. Highs will climb to the low 80s. Showers will probably linger through the night, with lows mainly in the upper 60s. Confidence: medium.

Monday hinges on the cool front pushing through strongly enough to clear the area out and bring another surge of drier air. If the front is slower to move on, showers could linger. Highs should be in the upper 70s to low 80s. Confidence: low-medium.

Read more about Capital Weather Gang’s confidence rating.

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