* Storms cut power in Virginia, spark house fires and water rescues in Montgomery County *

Radar & lightning: Latest regional radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

10:25 p.m. update: Occasional bursts of heavy rain and isolated flash flooding remain possible over the next few hours. That includes a heavy band of rain now leaving College Park, which flooded badly just yesterday. Most spots, however, have seen showers weaken and generally that trend should continue, though scattered showers could persist through the night and a few could be heavy. More showers and thunderstorms are likely tomorrow, especially during the afternoon into the evening, but can’t rule out some morning activity as well. The atmosphere is more stable tomorrow, so the severe threat is diminished from today, but it’s still really humid with highs near 80 to the mid-80s. This will be our last update for the night unless conditions warrant otherwise.

9:40 p.m. update: A targeted flash flood warning has been issued for Potomac, Md., until 12:30 a.m. in light of the torrential rains that have now moved out, but have caused flash flooding and prompted multiple water rescues. Another flash flood warning is in effect for southwestern Frederick County and far northern Loudoun County.

9:25 p.m. update: Torrential rains that clobbered Montgomery County and parts of D.C., northern Fairfax and northern Loudoun counties over the past hour or so are now confined to mainly east of I-270 and heading north-northeast away from the immediate area, but not before there were several water rescues in Montgomery County. Remember to “turn around, don’t drown” in those areas during the next couple hours until areas of standing water recede. Lingering rain across the area during the next few hours should be of the moderate to light variety. The tornado watch covering the D.C. area, and severe thunderstorm watch for central and southern Virginia and southern Maryland, have both expired.

8:54 p.m. update: That line of strong storms moving north through the western and northwestern suburbs has prompted a Severe Thunderstorm Warning for northern Fairfax, northern Loudoun, western Montgomery and southern Frederick counties until 9:30 p.m. In addition to very heavy rain and frequent lightning, damaging wind gusts to near or over 60 mph are possible. These storms will move northward across the warned area over the next hour.

8:35 p.m. update The main east-west band of heavy showers and thunderstorms is moving north of I-66 and will continue northward through areas mainly from around D.C. and I-95 toward points west, producing about 30 minutes of heavy rain and lightning. Behind that, a large batch of moderate to light showers should rain on pretty much the entire area for the next few hours. While some minor flooding is possible for low-lying areas in the western suburbs, we don’t expect anything severe with this trailing activity, and the tornado watch will likely be allowed to expire at 9 p.m.

7:20 p.m. update: Strong storms that dumped heavy rain on the western suburbs are heading north into Frederick County. No severe warnings are currently in effect in the metro area. The next wave coming from the south is now reaching areas from around Warrenton to Manassas. Some of this activity looks to be heavy again, and could cause some flooding problems as it moves north through northern Fauquier, northern Prince William, western Fairfax and Loudoun counties over the next couple hours. Areas further east, including DC proper and Prince George’s County may see more rain with this next wave than before, but generally speaking rains shouldn’t be as heavy from around DC/I-95 toward points east.

6:30 p.m. update: West of the Beltway, storms are lined up along I-66 from around Fairfax to Gainesville.  These are quickly lifting north.   Of concern, is the thunderstorm activity to the south in central Virginia which has its eyes on D.C.’s western suburbs later this evening.  It contains very heavy rain and may pose a flooding risk. We’ll keep you posted.

The tornado watch for the D.C. area and severe thunderstorm watch to the south remain in effect, but no severe weather warnings are currently active in the metro area (however, a tornado warning is now in effect for a sliver of northwest Virginia and the pandhandle of West Virginia until 7:15 p.m.). Scroll to the bottom of this post for overview information on these watches.

6:00 p.m. update: There’s a severe thunderstorm warning in effect for northwestern Prince William and central Fauquier County until 6:30 p.m., which includes Warrenton.  Gusty winds and small hail are possible with this storm.

While we cannot rule out isolated severe storms with damaging wind gusts and hail, we think the storm hazard of concern this evening may become flooding in our western areas. We are seeing a parade of storms with heavy rain  from central Fauquier County all the way into south central Virginia. (In northern Spotsylvania County, 2-3″ of rain has already fallen). These storms may “train” or track over the same areas this evening west of I-95 producing high rain totals.  Areas to keep an eye on for heavy rain are Fauquier, western Prince William, western Fairfax and Loudoun Counties, perhaps reaching western Montgomery and Frederick counties later tonight.

5:28 p.m. update: The cluster of thunderstorms around Fredericksburg looks like it wants to ride northward just west of I-95 and impact D.C.’s western suburbs in northern Virginia between around 6 and 8 p.m.  If you live right along I-95 and in the District, you may get grazed by these storms or they may miss.  East of I-95, chances are you see little  based on storm motion (unless the storms expand) from this batch.

5:00 p.m. update: Severe thunderstorm warning for eastern Spotsylvania County, city of Fredericksburg and southern Stafford County until 5:45 p.m.   A storm with very heavy rain and possibly some large hail in central Spotsylvania County is moving north at 20 mph.  These storms will be a hazard for folks traveling along I-95 in this area for the next 45 minutes or so.

While we continue to see a couple widely scattered  storms well west and north of the District, these storms impacting the Fredericksburg area are the ones to watch.  They will likely impact D.C.’s southwest and western suburbs between 6:00 and 8:00 p.m.  or so.

Note: there is no imminent sign of stormy weather for the immediate D.C. area inside the Beltway, but that could change as the evening wears on, so keep an eye on updates.

4:45 p.m. update: We’re starting to see widely scattered storms pop in the D.C. area. A thunderstorm is intensifying in southern Fauquier County, and moving north towards western Prince William County, around Haymarket.  A thundershower has also formed around Gaithersburg in Montgomery County, tracking towards just west of north towards Germantown.

Still no signs of any immediate severe weather in the D.C. area. The storms to watch are those getting close to Fredericksburg along I-95.

4:30 p.m. update: Storms in central Virginia are creeping northward up I-95.  A severe thunderstorm warning is in effect for eastern Spotsylvania County until 5:15 p.m.  Storm could produce hail to ping pong ball size and 60 mph winds.  If you’re traveling along I-95, use caution traveling through this region.

4:15 p.m. update: Radar remains mostly quiet in the region, while strong to severe storms continue to slowly move north through central Virginia.

I just spoke to CWG severe storm expert Jeff Halverson and, based on the evolution of storms so far, we think the risk of widespread severe storms in the D.C. area has gone down slightly. However, the atmosphere remains very unstable, so there is still the chance that strong to severe storms could develop with little notice. Also, the storms in central Virginia could still impact the region, but probably later than the 5-7 p.m. time slot we identified earlier and it’s not clear if they will hold together that late. Bottom line: remain vigilant, but the odds of widespread severe storms has dropped some.

3:45 p.m. update: Radar is quiet here in the D.C. metro region, but strong to severe storms are erupting in central Virginia. A tornado warning is in effect just south of Charlottesville (until 4 p.m.), and potent storms are forming in the vicinity of Richmond. We expect to see storms increase in coverage in the D.C. metro region starting around 5 p.m. – first in our western and southwestern suburbs.

Severe thunderstorm watch in effect until 10 p.m. (NWS) Severe thunderstorm watch in effect until 10 p.m. (NWS)

3:30 p.m. update: To the south of the tornado watch covering the D.C. metro area, a severe thunderstorm watch has been issued for  central and southern Virginia and southern Maryland, including D.C.’s far southern suburbs that include Stafford, Spotsylvania and St. Mary’s (Md.) counties until 10 p.m.

Overview, 3:05 p.m.

The National Weather Service Storm Prediction Center has issue a tornado watch until 9:00 p.m. for a large part of the Washington, D.C. metro region.

(The watch excludes counties adjacent to the Chesapeake Bay – namely Anne Arundel, Calvert, and St. Mary’s counties.)

Area shaded in red under tornado watch (NWS) Area shaded in red under tornado watch (NWS)

The hot and humid air has destabilized the atmosphere and, given some spin in the lower atmosphere, a few tornadoes could develop. While a few tornadoes are possible, the more common storm hazards will likely include: lightning, strong – possibly damaging – straight line wind gusts, hail, and heavy rain.

Detailed overview: Atmosphere primed for possible severe weather this afternoon and evening

This is a relatively low-end watch.  The National Weather Service indicates there’s about a 40 percent chance of 2 or more tornadoes in the watch zone (shaded area above).  There is a 30 percent chance of 10 or more occurrences of damaging straight-line winds (58 mph or higher) and 10 or more occurrences of large hail (1-inch in diameter or bigger).

Remember that a tornado watch means conditions are favorable for the development of tornadoes, but is not a guarantee. A watch is the equivalent to a yellow light: stay weather aware. However, if a tornado warning is issued, that means a tornado has been spotted or detected by radar and is imminent/occurring. A warning is equivalent to a red light: take action.

The safest place to be in a tornado is in the lowest level of a well-built structure in an interior room away from windows. Avoid mobile homes, trailers and motor vehicles.