Signs of a derecho-climate change link, ten years after the 2012 storm
Areas between Silver Spring and Hyattsville and Rockville and Derwood, where up to 5 to 7 inches of rain fell, saw the most rain. But a wide swath of southern Montgomery County, northern sections of the district and northern Prince George’s County saw at least 2 to 4 inches fall over several hours.
In addition to flooding, a severe thunderstorm that swept from Potomac to Rockville between 7 p.m. and 7:30 p.m. Saturday felled trees, including one on a housedisplacing residents.
As a result of the storms, there were nearly 17,000 power outages across Maryland Sunday morning, including about 12,000 in Montgomery County.
In total, the National Weather Service received 31 reports of flooding from Saturday night through Sunday morning and 10 reports of wind damage, mostly from downed trees.
Here is a summary of the flood reports:
- The road connecting the Beltway and Clara Barton Parkway was blocked due to high water.
- Rock Creek Parkway, Potomac Parkway and Beach Drive in northwest Washington were closed due to flooding. Many vehicles got stuck in high water.
- A flow gauge on the Northwest Fork of the Anacostia River soared 6 feet in an hour near Hyattsville. A flow gauge just east of Brentwood showed a rise of 7.2 feet in 50 minutes.
- A Hyattsville neighborhood near the intersection of 23rd Avenue and Sheridan Street was inundated with “several trapped or displaced people,” according to the weather service.
- Near Takoma Park the east-west highway was closed at Riggs Road when Sligo Creek overflowed. A vehicle became stranded near the intersection of New Hampshire Avenue and Sligo Creek Parkway.
- Just east of Silver Spring at Four Corners, three vehicles were stuck.
- Families have been displaced in Silver Spring due to flooded basements and electrical hazards.
- In Chevy Case, Beach Drive was closed due to Rock Creek overflow between Connecticut Avenue and Kensington Parkway.
- Near Aspen Hill, part of MD-28 was closed due to overflowing water from Rock Creek, and there was a water rescue along Village Lane and Rippling Brook Drive.
Pete Piringer, spokesperson for Montgomery County Fire and Rescue, tweeted that emergency teams responded to 449 incidents during the event.
Remarkably, while areas north of downtown Washington were flooded, very little rain fell to the south. Reagan National Airport recorded just 0.53 inches, while Dulles Airport reported nothing measurable.
The torrential rain was triggered by a very slow front pushing south through the region. The weather service issued a flood watch in advance, indicating the potential for several inches of rain. But the amounts exceeded forecasts in some areas.
It initially appeared that the region could avoid the worst in the late afternoon and early evening on Saturday when the rain was initially expected to start. Much of the storm’s activity was centered northwest of the region — near Frederick, Maryland, and to the west.
Summer in America is getting hotter, longer and more dangerous
But as the front sagged south after about 7 p.m., storms began breaking out in Montgomery County and rolling west to east repeatedly over the same areas, a phenomenon known as ‘coaching.
1210a: Extremely heavy rain from McLean through Silver Spring to Laurel…multiple stranded cars and water rescues in Montgomery County tonight. Stay indoors and do not try to cross a flooded road with your car. Avoid roads near creeks/streams. pic.twitter.com/hZWLrsGaAE
— Capital Weather Gang (@capitalweather) July 3, 2022
The storms were able to draw in tremendous moisture. It was a hot and humid summer day, and the precipitable water, a measure of moisture levels from the top of the sky down to the ground, was excessive.
The high-resolution NAM model simulated precipitation water values between 2 and 2.5 inches over the region – in record territory for early July.
In a special bulletin issued at 11:24 p.m. Saturday, the weather service wrote that precipitation rates could “reach 2.5 inches per hour.”
A few other factors intensified the storm. The weather service bulletin mentioned approaching “shortwave energy” from the Ohio Valley that helped sustain the storms late into the night. The storms also fed on each other. As a group of storms passes, their exhaust or cold outflow would help destabilize the atmosphere for other storms.
Finally, precipitation has likely been boosted by human-induced climate change. There is a well-documented increase in the intensity of the most extreme heavy rain events in the eastern United States, fueled by an atmosphere that is becoming warmer and more humid.
Climate change has increased humidity in DC, making it even hotter
This extreme precipitation event follows several others in recent years, including two historic floods in Ellicott City, Maryland, in 2016 and 2018 and one of the most exceptional downpours on record in Washington in July 2019, when 3.44 inches poured out in just one hour. .
Such events are likely to become more frequent and intense over the coming decades as temperatures continue to rise.