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Hundreds of trees were downed and hundreds of thousands of people lost power Tuesday afternoon and evening as three sets of storms swept through the Washington area. The storms were fueled by hot, moist air that swept into the region, and were fueled and sustained by strong high-altitude winds along the approaching cold front.
Two complexes in particular were responsible for the lion’s share of the damage. Both were arcuate, arc-shaped lines that ran from west to east. The first plowed from Washington County to Cecil County in northern Maryland in the late afternoon. The second struck northern Virginia, the District and central Maryland during the evening. Both brought down dozens of trees and power lines – some on homes and cars.
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A third, slightly less intense complex tracked across north-central Virginia and southern Maryland late in the evening, leaving behind scattered reports of damaging winds and at least one case of flash flooding.
In total, the National Weather Service received about 150 reports of damage from the three complexes. Pockets of hail, some as wide as half a dollar, also formed within the storms. PowerOutage.US reported that more than 70,000 outages still remained Wednesday afternoon, nearly 24 hours after the storm — most in northern Maryland.
All three complexes generated downdrafts of strong winds that slammed into the ground and spread outward. The National Weather Service received about 40 reports of winds between 39 and 70 mph. Here are some of the peak gusts recorded:
- Centerville: 70 mph
- Leesburg: 62 mph
- Washington Dulles International Airport: 60 mph
- Quantico: 59 mph
- Reagan National Airport: 52 mph
Within a one-county radius of Washington, concentrated areas of damage were reported near Chantilly, Olney, College Park and Bowie. Olney appeared to be the hardest hit, where trees damaged about 20 houses and about half a dozen families were displaced.
Damage was also extensive in College Park, where a man was seriously injured when a tree fell on a house. The weather service concluded that peak winds in the area reached 80 to 90 mph and that the winds were blowing in a straight line, ruling out a tornado.
608p: Radar shows very intense winds just east of College Park toward Greenbelt…probably headed for Glen Dale. Take shelter in this area, a microburst is possible with 60-70 plus mph winds. pic.twitter.com/2rddBQMpxr
— Capital Weather Gang (@capitalweather) July 12, 2022
“Straight-line winds from thunderstorms can cause tornado-like damage,” the weather service wrote in a study of the storm. “Expected winds in College Park as of yesterday evening are equivalent to a low-end EF1 tornado.”
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The storm that caused heavy wind damage in Olney and College Park is known as a long-track echo. A transverse echo, unlike a supercell, which is organized around a rotating updraft, is powered by a powerful downdraft. A surge of intense downwind causes the front of the squall line to curve outward, racing ahead of neighboring regions. Bow echoes often travel at high speeds of at least 40 to 50 mph.
556p: Intense storm from Olney to Arlington to Burke. College Park, Capitol Hill, Old Town, Fort Washington, you’re next. Strong winds, hail, lightning and downpours on the way. pic.twitter.com/ynqOH8bPla
— Capital Weather Gang (@capitalweather) July 12, 2022
The radar image below shows the bow moving over West Virginia, south of Romney, between 3 and 4 p.m., as observed by the Weather Service’s Storm Prediction Center. The weather service in Sterling, Virginia, issued a continuous series of severe thunderstorm warnings ahead of this storm as far south as the Chesapeake Bay.
The following figure shows the storm at 5:30 PM as it approaches Interstate 95. The shape of the rainbow is unmistakable. The northern end of the bow echo has evolved into a comma-head-like structure and may have contained a large vortex, as is common in this type of storm.
The strong downdraft along the leading edge of the storm generates an ominous-looking shelf cloud – where moist air is lifted several hundred feet, then condenses into a low cloud.
This comma northerly head generated a powerful downdraft that impacted the subdivision just south of downtown Olney at 6:00 p.m. An enlargement of the cell is shown in the following figure. The echo from heavy rain at the northern tip of the promontory is shown in the left panel. The right panel is Doppler velocity and reveals air currents hidden in the rain.
The white circle encloses the area affected by the gust, but the most extreme winds are contained in the pink subregion, just southwest of Olney. This is a strong flow off the radar, to the northeast. The green adjacent region represents a strong flow in the southwest direction.
Taken together, these two spots indicate a highly divergent airflow. The premise here is that an intense downdraft core hits the surface at an impact point shown by the white “X”. The white arrows indicate the bidirectional outflow from the point of impact. Winds in the pink region must have generated winds of at least 60 mph, possibly stronger given the size of the trees that were felled.
Many people hear a sudden roar as the wind quickly accelerates to high speed during a gust. After the storm, the extent of tree damage can seem incredible. Based on the level of damage and the roar, many assumed a tornado had occurred. But like the situation in College Park, the radar shows a diverging, straight-line wind pattern rather than the rotating signature that would be associated with a tornado.
As the bow echo approached, the ominous shelf cloud was a sight to behold. We received dozens of cloud photos from readers and share an example below:
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