By Jason Samenow, Ian Livingston, and Jeff Halverson
8 July 2019

(The Washington Post) – A month’s worth of rain deluged the immediate D.C. area early Monday, resulting in one of its most extreme flooding events in years. The record-setting cloudburst unleashed four inches of water in a single hour, way too much for a paved-over, heavily populated urban area to cope with at the height of the morning rush.

The sheets of rain, with nowhere to run off, turned major roads into rivers while streams and creeks shot up 10 feet in less than an hour. The rushing water stranded scores of people in their vehicles, poured into businesses and the Metro system, submerged cars in parking lots, swamped basements and caused some roads to cave in, forming massive sinkholes.

Motorists are stranded on a flooded section of Canal Road in Washington as record rains hit the Washington, D.C. region on 8 July 2019, causing major delays on roads and major power outages. Photo: Dave Dildine / AP
Motorists are stranded on a flooded section of Canal Road in Washington as record rains hit the Washington, D.C. region on 8 July 2019, causing major delays on roads and major power outages. Photo: Dave Dildine / AP

Montgomery County, northern Fairfax County and Arlington endured some of the most extreme rainfall.

At Reagan National Airport, Washington’s official weather observing location, 3.44 inches fell, with 3.3 inches coming in the 9 a.m. hour alone. The odds of rain this intense in any given year are less than 1 percent. […]

As the storm complex slugged through Alexandria and downtown Washington between 9 and 10 a.m., Cameron Run in Alexandria rose nearly 12 feet. It was in this hour that the National Weather Service declared its first-ever Flash Flood Emergency for the District (such alerts began in 2011), reserved for the most serious events which are “life-threatening” and “particularly dangerous” situations.

The maximum observed rainfall rates associated with the storms were incredible, reaching 4 to 6 inches per hour.

Some of the highest rainfall totals from across the region in Maryland included North Potomac with 5.55 inches and Gaithersburg with 4.64 inches. In Northern Virginia, top totals included 4.93 inches in Oakton and 4.5 inches in Arlington’s Westover neighborhood. Multiple locations in the District topped 2 inches, including Nationals Park.

Washington’s 3.44 inches of rain, observed at Reagan National Airport, topped its previous July 8 record of 2.16 inches from 1958. It became Washington’s seventh-wettest July day on record (since 1871) and ranked among the top 25 wettest days for the June-to-August summer months. It’s the third time in the past three years Washington has seen a rainfall event ranking among the top 10 wettest for July. [more]

How and why the D.C. area was deluged by a month’s worth of rain in an hour Monday