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Latest developments

  • A confirmed, damaging tornado swept through central Anne Arundel County between Edgewater and Annapolis, between 2 and 2:30 p.m. No injuries have been reported as of this time. (Scroll down for pictures and videos)
  • Another tornado was reported in Charles County near Wicomico at 1:50 p.m.
  • Widespread flash flooding was reported in Frederick County, Md., where there were at least six swift water rescues. Six to seven inches of rain fell in many areas.
  • The chance of tornadoes and severe weather has greatly diminished and sunny skies and lower humidity return Thursday. However, river levels will be much above normal and above flood stage in many instances.
A tornado moved through parts of Anne Arundel County, Md., on Sept. 1 as part of storms caused by remnants of Hurricane Ida. (The Washington Post)

7:00 p.m. — Flash flood watch discontinued, tornado watch expires (Final update)

Rain is ending (or has ended) in the western part of the region and will gradually taper off in our eastern areas over the next couple hours or so. The flash flood watch was discontinued and the tornado watch has been allowed to expire.

Looking ahead into Thursday and Friday, we welcome sunshine and lower humidity. The biggest issue will be river flooding due to all of the rain in our far north and west areas; major flooding is predicted for the Monocacy River around Frederick and moderate flooding for the Potomac River in Georgetown.

This will be our final update. Scroll down for more videos and photos of the Annapolis tornado and damage. Stay tuned for our PM forecast update that will post around 7:30 p.m. Tomorrow, we’ll have a detailed recap of the Annapolis storm.

6:55 p.m. — Drone footage of Annapolis tornado damage

6:40 p.m. — Back edge of rain advancing into our western suburbs

Radar shows the back edge of the substantial rainfall from near Frederick to Reston to Manassas. To the east, very heavy rain is falling along Interstate 95 and just to the east and could cause some ponding on the roadways. There are no severe storm warnings in effect over the region and the risk of tornadoes has significantly diminished. The greatest chance of any intense storms is over Southern Maryland where a vigorous line is passing through with lots of lightning and very heavy rain.

Heavy rain also continues to the north around Frederick, which remains under a flash flood warning.

Over the next hour or two, the rain will continue to push eastward, mostly tapering off around the Beltway and points west, including the waterlogged Frederick area. It may take until later this after, some time after 9 p.m., for rain to taper in our eastern areas.

5:30 p.m. — Line of vigorous showers and storms entering the region from the west; flash flooding in Frederick County

Radar shows a line of showers and storms approaching from the west and southwest, with locally heavy downpours. These are not severe at the moment but may contain a bit of lightning and gusty winds, especially in our southern areas, as these pass through over the next one to two hours.

To the north, very heavy rain continues in Frederick County, where a warning for “life-threatening” flash flooding is in effect from around Frederick to the Pennsylvania state line. About half of foot of rain has fallen around Frederick and up to 7 inches just to its northeast. The flash flood warning for this area was just extended until 8:30 p.m. as an additional one to two inches of rain are possible. The Weather Service reported flash flooding is occurring “across a large portion” of the county and that additional rainfall will “exarcerbate” the situation.

5:00 p.m. — Additional Anne Arundel County tornado and damage videos emerge

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

Posted by Alan Brentzel on Wednesday, September 1, 2021

4:15 p.m. — Maryland Gov. Lary Hogan reports “substantial damage,” no injuries from Anne Arundel County tornado

In a Twitter thread, Gov. Hogan (R) described reports of “substantial damage and trees down from Central Avenue in Edgewater to West Street in Annapolis. As of now, no injuries are associated with the storm.”

He added: “We are working with Anne Arundel County and City of Annapolis officials to assess the damage and determine what further resources are needed on the ground.”

4 p.m. — National Weather Service warns of more storms to come; tornado risk is down but not out

Radar shows numerous showers and storms in the region but nothing is currently severe. These storms will take several more hours to clear the region. The National Weather Service’s latest discussion says the environment is becoming somewhat less favorable for tornadoes but “some threat for severe thunderstorms can’t be ruled out.”

In northern Maryland, flooding has been a problem and a flash flood warning is in effect north of Frederick until 5:30 p.m. The Weather Service says between 3 and 5 inches have fallen and another 1 to 3 inches is possible. Numerous high water rescues have been required.

We will continue to monitor the flooding and severe weather threats and post updates.

3:30 p.m. — Some more pictures/video of Anne Arundel County tornado and damage

3:20 p.m. — Heavy showers and storms continue in region; no severe storm or tornado warnings at the moment

Following the tornado in Anne Arundel County, we have not seen any additional storm warnings. However, numerous showers and storms will cycle through the region over the next few hours and we cannot rule out more severe weather, including pockets of flash flooding or a tornado. The tornado watch remains in effect until 7 p.m.

3 p.m. — More reports of damage from Anne Arundel County and Annapolis tornado coming in

From the Anne Arundel County Office of Emergency Management: Confirmed trees, wires down, damage to buildings in Riva, Woodland Beach, Annapolis.

2:53 p.m. — Videos and photos emerge of Anne Arundel County tornado and damage

There are currently no active tornado warnings in Anne Arundel County as the responsible storm for the tornado has moved off to the northeast.

Numerous photos and video of the tornado are popping up on social media, which appeared to track just northwest of Shady Side through Londontowne to near and just west of Annapolis. Here are a bunch:

2:30 p.m. — Tornado warning for northeastern Anne Arundel County until 3 p.m.

The tornado-producing storm has reached the vicinity of Arnold and is sweeping north at 30 mph. The storm is moving in the direction of Lake Shore (arrival 2:40 p.m.) and Riviera Beach (arrival 2:45 p.m. arrival).

2:25 p.m. — Tornadic storm passing just north of Parole and Annapolis, toward Arnold

The National Weather Service confirmed a tornado was on the ground a few minutes ago in Anne Arundel County south of Annapolis. Recent Doppler radar scans indicate the rotation has weakened.

2:10 p.m. — Tornado on ground in Anne Arundel County, south of Annapolis

Radar has shown a debris signature indicative of a tornado and storm chaser video has confirmed a tornado on the ground. Seek shelter immediately if in the tornado warning zone (see 2 p.m. update), especially if you’re between Londontowne, Parole and Annapolis.

2 p.m. — Tornado warning for Anne Arundel County, including Annapolis until 2:30 p.m.

Radar indicates an area of rotation just east of Upper Marlboro which is racing northeast at 35 mph. Londontowne and Annapolis are in the potential path of this storm. The storm could reach Annapolis around 2:15 p.m. Seek shelter if in this zone.

1:35 p.m. — Tornado warning for south central Charles and northwest St. Mary’s County until 2 p.m.

The rotating storm coming out of Virginia’s Northern Neck (see 1:10 p.m. update) is now racing into south central and southeast Charles County and northwest St. Mary’s County. This storm is passing over mostly rural areas but could be near Mechanicsville by around 2 p.m.; seek shelter if in its path.

1:20 p.m. — Tornado warning for northeast Charles and southeast Prince George’s counties until 1:45 p.m.

Radar indicates a rotating storm west of Hughesville, racing north at 35 mph. This storm will pass mover mostly rural areas east of St. Charles, Waldorf, and Brandywine. Seek shelter immediately if in this zone.

1:10 p.m. — Tornado warnings over Virginia’s Northern Neck, these storms will affect Charles County

A rotating thunderstorm has triggered tornado warnings for northeast Carolina and King George counties that will expire at 1:15 and 1:30 p.m. This thunderstorm will move into Charles County after that and could pose a tornado risk.

Elsewhere downpours are developing south of the Beltway and surging north. They are not severe at the moment but need to be monitored.

Original article

The remnants of Ida are set to bring an active afternoon of high-impact weather to the Mid-Atlantic region on Wednesday, with the potential of tornadoes, damaging winds and flash flooding among the mix of hazards expected. Flash flood watches are in effect for the area, and so is a tornado watch, with flooding the main concern in our western zones and severe thunderstorms closer to the District.

A tornado watch means conditions are favorable for the possible development of a tornado, but there’s no guarantee it will happen. Stay alert. But if a tornado warning is issued for your location, it means rotation has been detected by radar or a tornado spotted on the ground and you should seek shelter immediately in an interior room, away from windows, at the lowest possible floor.

The prospect of severe weather Wednesday afternoon has prompted Montgomery and Howard counties to close school early. D.C. and Fairfax County Public Schools have canceled all after-school activities.

The day began with an early morning tornado watch for the region as rotating storms fired along a warm front lifting north toward the Mason-Dixon Line. At least one tornado formed Tuesday evening southwest of Blacksburg, Va., along Interstate 81, with additional tornado warnings issued overnight near Charlottesville.

By early this afternoon, a broken cluster of strong to severe thunderstorms with tornado and flooding potential will fire. The heaviest rain will come down over the Blue Ridge and northwestern areas, but there are increasing signs that training thunderstorms, or cells that move repeatedly over the same area, could dump up to one to three inches in the immediate D.C. area. However, amounts will be highly variable.

Washington received more than nine inches of rain in August, nearly triple the average value. Flash flooding will be made more likely by saturated soils that can’t handle much more water.

Activity will wind down after midnight, ushering in a cooler, more refreshing air mass.

At a glance

The Washington region is on the western edge of the National Weather Service Storm Prediction Center’s Level 3 out of 5 “enhanced risk” zone, which represents the great risk of tornadoes. Storms will fire just west of or near D.C., forming one or more broken lines as they push east.

  • Timing: 1 to 8 p.m. While that’s a wide window for storms, it’s likely that they will take their time crossing our area. Individual, potentially tornadic storms will move northeast, but the line within which they will be embedded will slowly shuffle eastward.
  • Main concerns: Tornadoes and flash flooding. Thunderstorms will probably rotate and could produce quick-hitting tropical tornadoes with relatively little warning. They will also have high rainfall rates, perhaps two inches per hour or more.
  • Secondary concerns: Damaging winds and frequent lightning. Setups like this often feature “moisture loading,” meaning the atmosphere traps a lot of water at the mid-levels that can drag down strong winds when it falls to the surface. That could make for a couple of wet microbursts, which would bring tiny corridors of very strong winds.

River flooding potential

During the deluges and in their wake, rivers — already at high levels from recent rains — will rise quickly.

Many locations are forecast to enter minor or moderate flood stage, and river flood watches have been issued accordingly for locations that are expected to reach flood stage in the next 48 hours. A few locations may even approach major flooding, especially across northwestern portions of the forecast area,” the National Weather Service wrote.

The Potomac River in Georgetown, for example, is forecast to reach moderate flood stage on Friday, while the Monocacy River in Frederick is predicted to reach major flood stage on Thursday.

Discussion

An active afternoon and evening are predicted for the Washington region as the remnants of Ida combine with a frontal boundary and energy in the upper atmosphere. During the transition of this post-tropical system into a fully mid-latitude storm, we are anticipating that one or more bands of dangerous thunderstorms will develop, producing localized flash flooding, wind damage and tornadoes.

The setup is shown below, which is a forecast surface map for 2 p.m. today. Ida’s remnant vortex becomes embedded in the front, with a warm front along the Mason-Dixon and a plume of tropical moisture drawn into the warm sector to its south.

Since last night, very heavy, steady rain has fallen to the immediate north and west of the system, as it interacts with an upper-level trough over the Great Lakes and comes under the influence of a jet streak (pocket of fast winds) in the upper-level westerly flow.

These dynamic interactions have greatly enhanced flooding rains on the system’s northern side, the worst of which have shifted away from the immediate D.C. region.

Along and especially north of the Mason Dixon, there is the prospect of life-threatening flash flooding today, along with significant river flooding arriving tomorrow into Friday.

The Washington region will find itself in a different regime of the storm — the more unstable zone called the “warm sector” to the south and east of the storm center. Although we will have deep and persistent cloud cover, the atmosphere is still unstable and is expected to become more unstable through the afternoon.

The flood threat in our region is conditional on bands of intense showers and thunderstorms, several of which may pass repeatedly over the same locations. Many locations across the region already picked up a quick one to three inches of rain from a rogue storm cell that tracked through during the early morning hours (more on that below). So, hydrologically, much of the area is saturated and primed with a low threshold for flash flooding.

The Weather Service remains concerned about the period between about 1 and 8 p.m., when multiple bands of storms are likely to develop. A predicted radar snapshot for 5 p.m. today, based on high-resolution forecast models, is shown below.

Working with an unstable atmosphere and abundant moisture, the approaching vortex has increased winds in the middle levels of the atmosphere. This belt of fast flow has increased the wind shear to 55-60 mph — quite an impressive value for early September. That deep shear is almost certain to organize thunderstorm cells into rotating types called supercells.

Low-level spin energy called “helicity” is also present in large amounts, especially along the warm front that will move through the D.C. region early this afternoon and in the developing warm sector. This low-level spin may help supercells concentrate their mid-level rotation into some tornadoes.

We anticipate that the tornadoes will be on the weak, brief and short-track side of the intensity spectrum; the risk may increase some northeast of the Washington region.

Supercell storms may also draw down momentum from the fast winds aloft to the ground, creating localized pockets of straight-line wind damage, or microbursts, as noted above.

What happened last night?

To the surprise of forecasters, a large, advance storm cell developed in central Virginia before midnight and tracked northeast through Washington and Baltimore. It awoke many in the region between 2 and 4 a.m. with remarkably frequent lightning, booming thunder, torrential rain and wind. The track of this supercell is shown above in the rain accumulation map, where dark reds stretch from Charlottesville to just west and north of the District.

Some locations in the immediate western suburbs of D.C. received two to three inches or more in the space of an hour. The intensity of this large cell was remarkable, given the hour of day, as was its isolated and long-lived nature.

The rogue storm caused widespread instances of flash flooding, downed trees and thousands of power outages. Difficulties during the morning rush hour continue to plague the region.

The cell initiated in the vicinity of Charlottesville where tornado warnings were issued for nearly two hours as it tracked into the Culpeper region. Thus far, there are no reports of actual tornadoes, but the supercell contained enough rotation aloft to concern forecasters. The cell developed within a small tornado-watch region covering part of central Virginia.

Around 1 a.m., the tornado watch was extended north into the D.C.-Baltimore region as forecasters anticipated the northern movement of this storm and the development of additional rotating cells.

The cell was part of a narrow, outer rain band heralding the initial approach of former hurricane Ida, and the low-level rotation in that band became strengthened along a frontal boundary draped across central Virginia. Tropical moisture that interacted with the supercell’s dynamics enabled phenomenally efficient rain generation. Lots of buoyant energy concentrated in mid-levels of the atmosphere led to highly concentrated lightning generation.

Meteorologist Matthew Cappucci explains how, when and where tornadoes form, and how climate change could be affecting these devastating weather events. (Joshua Carroll/The Washington Post)