Radar courtesy MyRadar | © OpenStreetMap contributors

* Flash flood watch through tonight *

4:20 p.m. — Severe thunderstorm watch discontinued as storms exit eastern areas; some damage in their wake

Radar shows the worst of the storms have passed to the north and east of Annapolis with just some lingering showers trailing behind them.

As the storms roared through the region, beginning early afternoon, they produced heavy rain and frequent lightning. A few of the storms unleashed damaging wind gusts that toppled trees, small hail and isolated flash flooding. Reagan National Airport clocked a gust of 58 mph as the storms rolled through, and a location just south of Annapolis registered at 66 mph gust.

The most serious incident occurred when a building under construction in Northwest Washington collapsed, trapping one person in the rubble and sending five to hospitals with injuries, according to the D.C. fire department.

As severe storms have exited the region, this will be our last update. Additional rain and storms, which could produce heavy rain and areas of flooding, are possible later this evening, starting around 8 and continuing overnight.

Stay tuned for our PM Update, which will have the details on the forecast overnight into Friday, which will publish around 5 p.m.

Peter Hermann contributed to this update.

3:55 p.m. — Tornado warning between Bowie and Annapolis discontinued, but intense storms hitting Annapolis area

The Weather Service says the tornado threat has diminished. However, a severe thunderstorm warning remains in effect from Severna Park through Annapolis until 4:15 p.m.

3:35 p.m. — Tornado warning from Bowie to Annapolis until 4 p.m.

Radar indicates possible rotation near Bowie moving east at 50 mph. The storm could reach Annapolis by 3:45 p.m. Seek shelter in interior room at lowest possible level if in path. Note that radar shows very strong winds, potentially up to around 70 mph.

3:30 p.m. — Severe storms pointed at zone from Bowie to Annapolis

While downpours linger inside the Beltway, the worst of the storms has pushed to the east and is bearing down on Bowie and will push east along Route 50 toward Annapolis in the next 30 minutes. Extremely heavy rain, lightning and some strong wind gusts are likely.

A flash flood warning continues in the District and close-in suburbs in Northern Virginia, but the heaviest rain has exited. The temperature downtown, at The Washington Post, dropped from 91 to 71 degrees as the storms passed.

Here are some visuals of the storm:

3:15 p.m. — Flash flood warning issued for District, Arlington, Alexandria, Falls Church

As between 0.5 and 1.0 inches have fallen in a short time in the District and close-by suburbs in Virginia, the National Weather Service has issued a flash flood warning. It cautions that another inch or two of rain is possible, which could cause “life-threatening flash flooding of creeks and streams, urban areas, highways, streets and underpasses.”

Remember, never cross a flooded road in your vehicle. Turn around, don’t drown.

2:47 p.m. — Severe storm sweeping into immediate area; warnings in effect

A line of intense storms stretches from Germantown to Manassas, with severe thunderstorm warnings along the entirety. It will hit the west side of the Beltway around 3 p.m. and cross the Beltway into our eastern suburbs by around 3:30 p.m. Heavy rain, frequent lightning and wind gusts up to 60 mph are possible. Seek shelter now if you are outside.

Here are a couple of visuals of what this storm looks like on approach and as it comes through:

2:25 p.m. Line of intense storms consolidating west of Washington, to hit beltway around 3 p.m.

From north of Germantown through Sterling to Warrenton, a line of storms has consolidated over the past 30 minutes and is headed for the immediate area, probably moving inside the Beltway around 3 p.m. Severe thunderstorm warnings accompany this line, which is expected to produce bursts of damaging winds in addition to very heavy rain and lightning.

Meanwhile, a more isolated but vigorous storm is pushing through the zone from Bowie to Severn and headed for Annapolis over the next 30 to 45 minutes. It swept through the area from near Great Falls through Potomac, Wheaton and Aspen Hill and has a history of producing hail and a few areas of damaging winds.

1:50 p.m. — Widely scattered storms flaring up, some severe

Over the past hour, storms have flared around the region, mainly north, south and west of the Beltway. One intense storm tracked from west of Great Falls through Potomac is now near Wheaton and will affect the zone from Silver Spring through Greenbelt to Odenton and Bowie over the next 40 minutes. Heavy rain, frequent lightning and strong winds are likely in this zone.

Another area of intense storms is just to the southwest of Fredericksburg.

Farther west, scattered storms have popped up between the north side of Culpeper and the east side of Frederick and are headed east. We still expect storms to be most numerous and affecting the largest portion of the immediate area starting around 3 p.m. or so.

1 p.m. — Severe thunderstorm watch issued until 8 p.m.

The National Weather Service has issued a severe thunderstorm watch for the Washington and Baltimore region through 8 p.m. The watch covers a broad portion of the Mid-Atlantic, stretching from south of Richmond to north of Philadelphia.

The Weather Service cautions damaging wind gusts could reach up to 70 mph.

A severe thunderstorm watch means that the atmosphere is conducive to severe storms and that you should stay weather-aware, but they are not a guarantee. If a severe thunderstorm warning is issued for location, it means a dangerous storm is imminent, and you should seek shelter.

Original article from 12:30 p.m.

A slow-moving but strong cold front running into steamy air lodged over the Washington region will act as the trigger for multiple rounds of showers and storms Thursday afternoon and evening.

Some of the storms could be severe, with localized bursts of damaging winds in addition to torrential rainfall and lightning. The National Weather Service has signaled that it’s likely to issue a severe thunderstorm watch for the region.

As there may be multiple rounds of storms and some areas could get hit by downpours repeatedly, flooding is also a concern. The Weather Service has issued a flash flood watch through Thursday night and is predicting one to three inches of rain and the potential for locally higher amounts.

“Heavy rain in short periods of time will cause the potential for streams and creeks to quickly rise out of their banks as well as the potential for flash flooding in urban areas,” the Weather Service cautioned.

Storm threat at a glance

Timing and duration: The first round of storms is likely to enter the region between 2 and 5 p.m. from west to east, probably affecting the Beltway and Interstate 95 corridor around 3 or 4 p.m. This initial round may be the most intense. After that, a pause is possible, with more showers and storms a good bet between 7 and 9 p.m. They continue intermittently into the predawn hours Friday.

Likely hazards: Heavy rain, lightning, gusty winds.

Possible hazards: Flooding, damaging winds, hail.

All clear: A little after sunrise Friday.

Discussion

Thursday’s weather setup is shown in the forecast surface map below. We remain on the hot and humid side of a cold front slowly advancing into the Mid-Atlantic. Ahead of this front streams a deep plume of high humidity, ushered in by winds streaming from the south-southwest.

In the higher atmosphere, a wavelike disturbance will be passing through, promoting widespread uplift of air across the region (not shown). That disturbance is also “freshening” the winds (increasing their speed) such that a wind shear — or increase in wind velocity with altitude — will develop.

All of these factors have ramifications for Thursday’s weather threats: a juicy atmosphere, an unstable atmosphere and one with energetic wind currents.

First, let’s delve into the severe weather threat. The Weather Service’s Storm Prediction Center has placed our region in a slight risk zone, Level 2 out of 5, for severe thunderstorms. The combination of an unstable atmosphere and modest amounts of wind shear suggests that clusters of thunderstorms will self-organize into strong, long-lasting aggregates later Thursday afternoon and evening.

The approaching cold front and a precursor zone of weak low pressure to the east of the Blue Ridge will assist in building clusters into one or more lines of storms. We use fine-scale models to examine the simulated evolution of thunderstorms, and one of these is shown below, valid at 4 p.m.

The simulation shows a robust storm line that has congealed over the Blue Ridge, ahead of the advancing cold front. This line moves into the I-95 corridor between 3 and 5 p.m. with heavy rain, lightning and locally strong to damaging wind gusts (perhaps in the 60-70 mph range). Other fine-scale forecast models show a similar evolution.

One factor that could moderate the intensity of thunderstorms is morning cloud cover across the region; if this cloud cover persists through early afternoon, it may tone down the vigor of buoyant air currents.

Our second threat is the prospect that some of those torrential downpours could persist and lead to local zones of flash flooding. We’re also in a slight risk zone for flash flooding late Thursday afternoon and evening. This is because of the combination of very humid air streaming parallel to a slowly moving cold front. This can set up repeated passage of storm cells over the same locations, like a train, allowing rainwater to rapidly accumulate.

The guidance provided by the fine-scale models indicates hourly rain totals of one to three inches are possible, perhaps more in a few places. But it is impossible to foretell where those discrete, small zones may set up hours in advance because they are tied to the initiation and evolution of individual thunderstorm cells.

The good news is that the overall pattern (including the plume of tropical moisture, cold front and disturbance aloft) appears to be more progressive in recent model runs, compared with those a couple of days ago. In other words, there is less likelihood that the entire setup will stall across the region through the second half of Friday.

There will be quite a bit to focus on Thursday afternoon and into evening. Capital Weather Gang meteorologists will provide updates on any watches and warnings for these myriad threats and will be closely monitoring radar and other data into the evening.