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Inside the Annapolis tornado: How Ida powered this destructive storm

The Weather Service found the twister was on the ground for 11.25 miles and rated it an EF-2 with 125 mph winds

A tornado moved through parts of Anne Arundel County, Md., on Sept. 1 as part of storms caused by remnants of Hurricane Ida. (Video: The Washington Post, Photo: @RobbMDWxMedia/The Washington Post)
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The high-impact “second act” of former Hurricane Ida played out across the Mid-Atlantic on Wednesday with multiple tornadoes and deadly flash flooding — including the significant twister that tore through central Anne Arundel County. The tornado carved an 11.25 mile path from near Shady Side to just north of Annapolis, the National Weather Service determined Thursday.

The tornado was widely captured on video and shared on social media. It appeared as a large, swirling mass lofting debris as it charged northward at more than 30 mph. It was on the ground from 2:00 to 2:23 p.m.., when a tornado warning was issued for the affected zone. The Weather Service’s preliminary damage survey indicated the twister was up to 200 yards wide and rated it an EF-2 on the 0 to 5 scale for tornado intensity. Winds were as high as 125 mph.

A tornado this strong in Maryland and the Mid-Atlantic is somewhat unusual; most tornadoes in this region are rated EF-0 or EF-1.

Annapolis Mayor Gavin Buckley (D) said the tornado destroyed three buildings in the city and left 24 structures condemned. In addition, 26 buildings suffered major damage, and 49 had minor damage.

After Annapolis tornado spawned by Hurricane Ida, recovery efforts begin

The Annapolis tornado was one of three confirmed in Maryland:

  • A tornado was reported and captured on video in Dorchester County near the town of Hurlock, about 15 miles east of Cambridge. The National Weather Service rated it EF-0 on the 0 to 5 scale for tornado intensity. It was on the ground for 4 miles, with peak winds of 75 mph. It damaged a metal building and overturned several irrigation systems.
  • The Weather Service confirmed a tornado tracked through eastern Baltimore County near Edgemere; it rated that tornado an EF-0 with 85 mph winds and found numerous instances of tree damage.
  • Law enforcement noted a tornado in Charles County near Wicomico, but there was no known damage from it. The Weather Service said that the tornado is unconfirmed but was surveying the area Thursday.

Destructive tornadoes also struck New Jersey and Pennsylvania on Wednesday.

New Jersey, Pennsylvania and Maryland slammed by tornadoes from Ida’s remnants

The twisters were set into motion by the spin from Ida’s remnant circulation and were intensified by the temperature contrast as the system merged with a cold front over the eastern United States. Ahead of the cold front, warm, humid air surged up the East Coast, creating a very unstable atmosphere. As the cold front and Ida’s remnants encountered the volatile environment, multiple rotating thunderstorms erupted.

Wow… at Plane Tint home airport (this was at Lee airport in edgewater facing rt2.)

Posted by Alan Brentzel on Wednesday, September 1, 2021

How the Annapolis tornado evolved

The Annapolis tornado came in the wake of a powerful, long-track thunderstorm that swept from near Charlottesville through Northern Virginia and into Montgomery County, Md., before dawn Wednesday. That initial storm unloaded one to three inches of rain and produced instantaneous rain rates up to four to five inches per hour. It was the source of the fatality in a Rockville apartment subject to a flash flood. The cell also generated an extreme amount of lightning.

After a morning pause, heavy rain bands in the humid, unstable air ahead of a cold front, known as the warm sector, began sweeping through the Washington region. The graphic below shows all warnings issued during the storm event, along with reports of flash flooding (the green icons).

The multiple rain bands are shown in the radar scan below. In general, three bands developed, and the eastern band in particular generated a number of tornado warnings as embedded cells acquired rotating updrafts. This band formed along the axis of most unstable air, and it also had access to very strong, deep winds that increased in altitude and changed direction with height, generating what is known as wind shear. Such strong wind shear helped sustain the updrafts.

The strong shear was created from a combination of rapidly increasing wind speed with altitude — as Ida’s vortex flow aloft overspread the region — and locally generated shear in the lower atmosphere, along the warm front draped over north-central Maryland.

The rotating updrafts, called mesocyclones, showed up on Doppler radar, and a compilation of these rotating storm or supercell tracks is shown below. The supercell from early Wednesday morning can be seen crossing through the District, and the supercell track that spawned the Annapolis tornado is also shown to the right.

As opposed to the intermittent showers in the warm sector, steady and heavy rain was the rule just to the north and west of the storm center. Here, a plume of tropical moisture from the south was drawn over the warm front, and dynamic uplift from the jet stream intensified rainfall.

As rain bands developed, they repeatedly swept across north-central Maryland, laying down an impressive swath of six-to-eight-inch rain totals and fairly widespread flash flooding in Frederick County.

Radar-estimated rain totals are shown in the graphic below.

The Annapolis tornado, however, was the headliner in the region from the remnants of Ida. The extensive damage made clear this was something stronger than a typically weak, garden-variety tropical cyclone-spawned tornado.

The Doppler view of the tornado’s signature is shown in the final figure below. A triad of characteristics identified this as a substantial tornado on the ground. These included a “tight” velocity couplet showing strong motion approaching the radar in green opposed to strong motion away from the radar in red (middle panel) and a very striking tornado debris signature (right panel).

Karina Elwood and Justin Wm. Moyer contributed to this report.