Multiple waves of severe storms swept across the Washington region Thursday afternoon and evening, leaving behind thousands of power outages, damage and several minor injuries.

The day’s most intense drama unfolded when the National Weather Service in Sterling, Va., issued a rare tornado warning for portions of Arlington, Alexandria, the District and central Prince George’s County around 9 p.m. The White House, Capitol and the National Mall were all within the warning zone.

The Weather Service has confirmed two tornadoes touched down Thursday evening between Arlington and the District around 9 p.m.:

1) An EF1 tornado, on the 0 to 5 scale for tornado damage, tracked from the Cherrydale neighborhood of Arlington to near 16th Street and Constitution Avenue NW in the District, along the Mall, with maximum winds of 90 mph. It was as wide as 125 yards on its 4.4-mile path.

2) An EF0 tornado touched down inside the District, one mile northeast of the Capitol in the H Street Corridor, and continued for 0.75 miles into Kingman Park. The tornado had a maximum width of 75 yards and peak winds of 80 mph.

Both tornadoes were spawned by the same rotating storm as it tracked across the area.

The storm toppled scores of trees along a path that began in Falls Church, before the tornado warning was issued, and that continued through Arlington, the Mall, Southeast Washington and Capitol Heights in Maryland. In its survey of the storm damage, the Weather Service determined tree damage in east Falls Church and the Westover and Virginia Square areas of Arlington was due to straight-line winds rather than a tornado.

The most concentrated tornado damage occurred in the Waverly Hills and Cherrydale neighborhoods in Arlington, where the twister first touched down at 8:59 p.m., according to the Weather Service.

“We have severe damage — three giant trees down — damage to an attached greenhouse, a smashed shed and power lines down and possibly more damage,” wrote Dakota Springston on Capital Weather Gang’s Facebook page, describing the scene on North Quebec Street in the Waverly Hills community. “The neighborhood has lots of other damage.”

Matthew Lovell described more damage in Arlington’s Cherrydale neighborhood, where the twister headed next and reached its greatest intensity, according to the Weather Service. “Lots of debris. Wood paneling from fences and the dumpster enclosure are scattered about the parking lot,” he wrote in a Facebook post. “My building shook. The insulation from my hvac closet was blown under the door into my living room. The toilet bowl water was almost empty. There are tree limbs stripped of bark on the ground.”

The Weather Service said some homes in the Cherrydale neighborhood had siding removed, before the twister moved into the Lyon Village neighborhood in Arlington, bringing down some trees.

Damage became “hard to identify” as the tornado moved over urban Rosslyn, the Weather Service said, but “emerged again” after it crossed the Potomac into the District. Wind damage to trees on the National Mall “was prominent from 23rd St NW east for 0.75 miles to near 16th Street NW south of The Ellipse,” the Weather Service said. It added that the tornado “lifted up and twisted” fencing installed for the Independence Day celebration, “landing in a mangled and haphazard manner” before the twister dissipated at 9:05 p.m.

But, three minutes later, the rotating thunderstorm dropped the second but weaker tornado in the H St. corridor. On the ground for just two minutes, the Weather Service found only scattered, “intermittent” tree damage. “Several hardwood trees were downed in Rosedale Recreation Center property, falling due west,” it wrote.

So how in the world did this happen?

Why were there tornado warnings and rotating thunderstorms?

The storm line that gave rise to the tornado warnings across D.C. developed as a second wave of storms, distinct from an earlier batch in the afternoon. That first batch impacted the District around 3 p.m., unleashing a 58 mph gust at Reagan National Airport, while the evening event began around 8:45 p.m. and produced a gust to 52 mph at the airport.

A broad radar view, below, reveals that the second wave took the form of an arrow- or arc-shaped complex of intense cells spanning Montgomery County through the District, Arlington, Alexandria and Fairfax County:

Note that the most intense cells traversed D.C. from about 8:45 to 9:15 p.m. and featured a prominent bulge. The red polygon is one of a series of tornado warning boxes issued by the Weather Service. The radar scan was obtained by the Doppler radar at Sterling in Loudoun County (near Washington Dulles International Airport).

To focus in on the bulge, let’s take a view from a different Doppler radar, one that is much closer and offers a different viewing angle — the Terminal Doppler radar at Reagan. The scan below was obtained at 8:53 p.m.

From proximity, the bulge shown in the previous view from Sterling morphs into a well-defined hook echo, which is indicative of a small area of rotation called a mesocyclone. Some mesocyclones (but not all) condense a region of their spin into a tornado.

That hook echo maintained its form as the cell crossed the District. A later scan from the National Airport radar is shown in the next image below, from 9:11 p.m., as the storm was exiting D.C. As part of this figure, we’ve included the corresponding Doppler velocity scan on the right. Shown is a pair of strong outbound and inbound velocities closely juxtaposed, a feature called a “velocity couplet.” “X” marks the spot of the mesocyclone.

Was the storm cell a supercell or some other type of storm complex?

The bulging cell with the hook could be classified as a supercell, or rotating thunderstorm. Alternatively, the mesocyclone was part of a larger complex called a “quasi-linear convective system” (QLCS). In a QLCS, lobe- and cleft-like features along the leading edge are generated by embedded mesocyclones. The difference at this point is somewhat academic.

What triggered the rotating storm so late in the evening?

This is a particularly interesting question, since this was a second wave of activity that occurred hours after the initial batch midafternoon with much more widespread severe activity (including large hail and damaging wind reports).

That first batch processed the bulk of the unstable air, ahead of the approaching cold front, but just enough remained. This second wave was triggered right along the cold front itself, which helped provide the concentrated uplift of air. But the relative paucity of lightning compared to earlier activity testifies to greatly reduced, unstable air.

The wind shear (increase in winds with altitude) did increase significantly through the evening, as the core of the upper-level disturbance passed through. That shear no doubt increased the tendency for these late cells to rotate.

How common are tornadoes in the Washington region?

Tornado warnings are unusual for the city. The area in D.C. covered by the tornado warnings Thursday night has seen only two others since comparable storm-based warnings began in 2007.

Most recently, there was one in May 2019. Before that, the last occurrence was October 2014.

Actual confirmed tornadoes last hit the city in April 2017. A storm similar to Thursday night’s crossed the area, dropping two weak twisters in the District and several others elsewhere. One caused damage at the Tidal Basin. Before that event, only two days in the modern record since 1950 have produced twisters inside Washington.

Across the broader Mid-Atlantic, the so-called tornado season statistically peaks in July. It’s a similar story in the immediate D.C. area, with a peak often coming during the summer months of June or July. In both cases it more or less coincides with when thunderstorms are most numerous and frequent in the region.

April and September can also be active tornado months in the region and have produced memorable events. Stronger tornadoes tend to favor these shoulder months given increased wind shear, a critical ingredient for tornadoes, compared to the summer.

About 85 percent of tornadoes in the local area are rated F/EF0 or F/EF1 on the 0 to 5 scale for tornado damage. These lower-end tornadoes are capable of significant property and tree damage, but tend to be easily survivable if protected from trees.

Stronger tornadoes have occurred in the region as well, but much more rare. Examples include the F3 College Park tornado of 2001 and the La Plata F4 twister in 2002 still fresh in many people’s minds.

The area served by the Weather Service office serving the Washington-Baltimore region averages about 12 tornadoes per year. In Virginia it’s about 18 and in Maryland roughly 10.

Visuals of the storm and its damage from social media

Sky and storm scenes

Damage photos

Arlington

The District