* Flash flood watch until 11 p.m. | Severe thunderstorm watch until 10 p.m. for Interstate 95 and east *

8:00 p.m. - Showers, some thunder in some areas for a few more hours. Tomorrow brings another chance of late day showers and storms.

Showers and a few thundershowers continue to track along Interstate 66 and Rt. 50 from west to east and just to the south. But none of the activity is severe. Here is the outlook for the rest of tonight and tomorrow.

Through Tonight: Scattered showers and storms continue to roam into the early night, but they should be generally waning as we lose daytime heating. After the main rain threat ends, it’s partly to mostly cloudy with temperatures in the upper 60s and lower 70s. Some patchy fog is likely to develop late as winds are light and variable, plus moisture is plentiful.

Tomorrow (Wednesday): No major changes to our pattern for now. Clouds are dominant before showers and storms develop in the afternoon. Some could be strong, although the risk for organized storminess may be slightly lower than recent days. Highs head for a near 80 to mid-80s range. Winds are from the south around 5 to 10 mph

Unless we see any new severe weather breaking out, this will be the last update of the evening. Have a great night.

7:30 p.m. - Severe thunderstorm watch canceled in western areas

Showers and storms have now shifted mostly east of Interstate 95, except for areas southwest of the Beltway extending to around Manassas.

No storms in the area are severe and the severe thunderstorm watch has been discontinued west of Fairfax and Montgomery counties. We anticipate it will probably be lifted for the rest of the immediate area before long.

We could have a few scattered showers and storms continuing into late this evening, but the odds of anything severe are pretty low.

We’ll post another update around 8 p.m. and that may be it for the night.

7:00 p.m. - Showers and storms passing through immediate area, but not severe

Radar shows a cluster of showers and storms stretch from Manassas (to the west) to Annapolis.

While the western area of this complex was briefly intense between Warrenton and Manassas, it has lost some steam. Still, there is some heavy rain and lightning around Burke and Franconia.

This activity should push east-northeast through the area over the next hour and it’s possible there’s a break behind it. On the other hand, new storms may fire up or back build along the western fringe of the complex keeping the storminess going some time longer.

6:10 p.m. - Storms delayed but not denied - rapidly increasing west and southwest of Washington

Storms have quickly fired up in northern Virginia from near Warrenton east-northeast through Centreville and into southern Alexandria. Some of these storms contain heavy rain, lightning and strong winds.

In fact a severe thunderstorm warning cover the area from Warrenton to Nokesville in western Prince William County through 6:45 p.m. mainly for the possibility of some damaging wind gusts.

All of this storm activity is moving east-northeast along Interstate 66 toward the southern half of the Beltway and the District which should expect storm conditions for the next hour, at least.

5 p.m. - Storminess off to slow start, mostly confined well south of Washington, but still need to monitor possible evening development.

The Beltway area is free of showers and storms with the closest activity south of Dale City. Short-range models continue to suggest more showers and storms should pop up this evening between 6 and 9 p.m. although these models have been a little overly aggressive in their forecasts for storms up to this point.

We’ll continue to monitor. We’d be surprised if there are not some showers and storms in the immediate area this evening, but widespread severe storms and/or flooding may not materialize. That said, there’s enough instability (from all of the heat and humidity) in the atmosphere that a few intense storms cannot be ruled out.

Our next update will be around 6 p.m. (or sooner if conditions warrant).

4:10 p.m. - Storms may start to increase after 5 p.m.

Radar is rather quiet showing just one isolated storm in southern Fauquier County. Our short-term models suggest storms may begin to increase in coverage and intensity after 5 p.m. and for conditions to remain unsettled with on and off showers and storms through 10 or 11 p.m.

While we can’t rule out some isolated severe storms in our region, the most intense activity may focus to our northeast and to our south, where there is greater wind shear - which helps sustain and strengthen storms.

We’ll update again around 5 p.m. (or sooner if conditions warrant).

2:50 p.m. - Severe thunderstorm watch until 10 p.m.

The National Weather Service has issued a severe thunderstorm watch in effect until 10 p.m. that includes the Washington and Baltimore metro areas.

A severe thunderstorm watch means conditions are favorable for severe storms and that you should remain weather-aware, but storms are not guaranteed. If a severe thunderstorm warning is issued for your location, on the other hand, it means a storm is imminent and that you should seek shelter immediately.

Original post

Much like Monday late afternoon and evening, showers and storms are likely to develop Tuesday, and some could be heavy.

The area is under a flash flood watch considering the possibility that some areas may get hit repeatedly by waves of storms. Any flooding should be isolated rather than widespread. Low-lying areas near creeks and streams as well as poor drainage areas will be most susceptible.

Some of the storms Monday were borderline severe with isolated pockets of damaging winds and hail. We run that risk of severe storms again Tuesday, but, on balance, the storms should be slightly less intense. Even so, the National Weather Service has indicated there is a 60 percent chance it will issue a severe thunderstorm watch again.

Like Monday, prime time for storms should be between about 4 and 7 p.m. Tuesday, but they could initiate as early as around 3 p.m. (especially in our western areas) and linger until 10 or 11 p.m. in some areas. While any individual storm may not last all that long (30 minutes or less), it’s possible that some areas will see multiple rounds.


Lightning photographed in storms Monday. (Carol Jean Stalun/Flickr)

Storm dashboard


(The Washington Post)

Approximate storm initiation time:

  • 2:30 to 4 p.m. in western areas.
  • 3:30 to 5 p.m. in immediate area, including the Capital Beltway.
  • 4 to 5:30 p.m. in areas east of Interstate 95.

More than one round of storms possible.

All clear: after 11 p.m.

Storm duration: 30 minutes or so, but more than one round possible.

Chance of measurable rainfall in any location: 65 percent.

Storm motion: west to east.

Likely storm effects: heavy rain, lightning, gusty winds.

Possible storm effects: damaging wind gusts, flash flooding, hail, isolated tornado

Rainfall potential: highly variable; average may be 0.5 inches, but some areas could see two to three inches, while some areas could end up with little rain.

Discussion

Tuesday and the next few days, we enter a weather pattern that is very typical of summertime in the lower Mid-Atlantic — a plume of very moist, unstable air that pinwheels clockwise around the Bermuda High, which is anchored over the western subtropical Atlantic. This sets the stage for daily showers and thunderstorms timed to the late afternoon and evening.


Forecast surface weather map for midafternoon Tuesday. Dark green arc east of Mississippi defines the corridor of high-moisture, unstable air arcing around the Bermuda High over the western Atlantic (not shown). (National Weather Service)

A clear focus for storms is lacking, with the nearest front retreating northward into northern Pennsylvania through Thursday. The jet stream aloft has weakened, but small ripples of energy (often hard to identify) will stream through, triggering off batches of storms now and then.

The overall flow is progressive, meaning storms will be on the move (as opposed to stalling out), but the very deep, moist atmospheric layer means locations that receive one or more cells in succession could pick up locally heavy rainfall, as much as two to three inches.

Additionally, the combination of significant instability later Tuesday afternoon, and modest levels of wind shear (the increase in winds with altitude, which helps to organize longer-lived, stronger storm cells) raise once again the specter of isolated strong to severe thunderstorms.

According to the Weather Service’s Storm Prediction Center (SPC), Tuesday’s threat is greatest in the direction of Baltimore and northeastern Maryland, which is in the slight risk zone (level 2 out of 5). The rest of the area is in a marginal risk zone (level 1 out of 5).


Threat of severe storms on Tuesday. (National Weather Service)

Tuesday’s wind shear levels over D.C. are weaker than those of Monday. Several impressive storm cells, which featured significant lightning, a smattering of wind damage reports (downed trees) and, in St. Mary’s County, golf-ball-size hail, developed Monday.

With weaker shear, overall thunderstorm intensity may be a notch lower, but isolated damaging gusts, a couple of pockets of hail, and frequent lightning cannot be ruled out for anyone.