Flood Watch through late tonight  | Live radar | Power outage tracker | Two people killed by Virginia tornado

8:50 p.m. update: With storms off to our east, it should be a mostly calm if breezy night. It stays mostly cloudy as winds shift to the west and northwest. Lows are in the low-to-mid 40s.

We’ll see those winds pick up with time, especially on Thursday when gusts past 35 mph are possible. Skies are partly to mostly cloudy on Thursday with highs in the mid-40s to near 50. A few showers may roam in the afternoon.

Stop by Thursday for post storm coverage and an explainer.

Storm overview

  • Timing: 4 to 9 p.m. A particularly strong line of storms with heavy rain and strong winds will come through the region between about 5 and 8 p.m. from southwest to northeast.
  • Coverage: Widespread showers and thunderstorms.
  • Storm motion: Southwest to northeast
  • Storm duration: 20 to 30 minutes, but multiple showers and storms possible
  • Likely impacts: Heavy rain, gusty winds
  • Possible impacts: Damaging winds, flash flooding, small hail
  • Cannot rule out: Isolated tornadoes, large hail

8:30 p.m. update: It just won’t quit for far southern St. Mary’s as another tornado warning was issued down there. The line is inching past them though, so it should be coming to an end soon. Since that’s not really the heart of our area, we’re going to get this wrapped up. You can keep track of tornado warnings, if any others come out. We’ll have full details on what happened everywhere in our recap tomorrow.

A quick forecast for the night and into Thursday in a few…

8:00 p.m. update: Storm activity has wound down across our general area, but parts of St. Mary’s County and Calvert County are still in the thick of it. It seems the tornado threat there should be just about over, but one more cell is in line so don’t let your guard down just yet in that region. Elsewhere, it’s much quieter.


8:00 p.m. radar.

7:50 p.m. update: Check out this great compilation of video and photos from today’s events.

Social media videos and photos show strong storms and high winds in the D.C. area. The entire D.C. area is under tornado watch through 11 p.m. Wednesday night, and flash flooding is possible. (Victoria Walker/The Washington Post)

7:42 p.m. update: Another tornado WARNING has been issued for St. Mary’s County. People in this area should seek shelter once again. The line of storms has largely moved out into the bay but it’s still moving over far southern Maryland.

7:28 p.m. update: A flood warning also continues for the area highlighted below, including D.C., until 10:00 p.m.


Flood warning until 10 p.m. (IEM)

A snippet from NWS on the situation:

AT 723 PM EST…REPORTING GAUGES INDICATED FLOODING ACROSS THE WARNED AREA. SPECIFICALLY…FLOODING WAS OCCURRING OR IS EXPECTED TO BEGIN SHORTLY ON ROCK CREEK…SLIGO CREEK…ACCOTINK CREEK…CAMERON RUN…AND NUMEROUS SMALLER TRIBUTARIES IN THESE AREAS. FLOODING WILL CONTINUE FOR SEVERAL HOURS. DO NOT DRIVE INTO AREAS WHERE WATER COVERS THE ROAD.

7:20 p.m. update: Streams and rivers continue to rise across the area followig the heavy rain. A flood warning has been issued for Loudoun and northwest Fauquier. Similar can be expected to occur in other places, warning or not.

7:12 p.m. update: The tornado watch is starting to shrink. Areas west of the city/I-95 have been canceled. The tornado threat is done in the city as well, so we’ll likely see the watch continue to be dropped further east with time.

7:06 p.m. update: Tornado WARNING for parts of Calvert and St. Mary’s Counties. Take cover in this area!

7:00 p.m. update: Rain from this line is coming to an end in D.C. and it has ended west of town. The eastern Beltway and east will see things wind down over the next 30-60 minutes. A flash flood warning was hoisted for Fairfax County and Alexandria. The warning runs until 8:45 p.m., but water should be subsiding before then.


Radar as of 7 p.m.

6:50 p.m. update: Power outages have spiked to around 20,000 in the local area over the past hour or so. The majority are in northern Virginia with around 12,000 there. Montgomery County is checking in with around 5,000. Several hundred are out in the city.


Power outages as of 6:50 p.m. (Washington Post)

6:45 p.m. update: Right as rain begins to end, another pulse of pretty strong winds. This is pushing through D.C. now.

6:40 p.m. update: The core of these storms continues to push east of I-95, and the back edge is moving into D.C. now.


Radar loop of storms moving through the mid-Atlantic. (College of Dupage)

6:30 p.m. update: Taking a broader view of today’s severe weather, we’re closing in on 200 reports across the East Coast. The worst of it, including a number of tornadoes, has been south of the area in Virginia and North Carolina.


Storm reports so far today. (Storm Prediction Center)

6:22 p.m. update: D.C. is under a flood warning until 10 p.m. This is primarily for areas of standing water and poor drainage.

6:18 p.m. update: Some of our far southern suburbs were not yet warned. So they join the show. Parts of Charles County and surrounds are under a severe thunderstorm warning until 7:00 p.m.

6:10 p.m. update: The worst of the storminess is lined up near I95 now, and about to begin leaving the city. In addition to the numerous hail reports around the city, winds gusted as high as 60 to 70 mph in Montgomery County near Germantown. A few other reports of trees down have come in mainly from western suburbs so far.


Radar at 6:10 p.m

6:06 p.m. update: Fortunately this line of storms is moving quick, because it’s causing some flooding since it’s been so wet recently. Flash flooding will remain at least a localized concern as it moves through.

6:00 p.m. update: With this line racing east, it’s no major surprise that our eastern suburbs are now also under a severe thunderstorm warning, until 7:00 p.m. There’s a risk of damaging winds and small hail in addition to heavy rain as it passes.

5:57 p.m. update: In addition to winds, small hail has been quite common in these storms.

5:50 p.m. update: This line is pushing into DC now. Looking impressive! Best to wait it out until it passes.


Radar at 5:50 p.m

5:45 p.m. update: Another severe storm warning up for northern suburbs. This is also mainly for the potential for strong winds to 60 mph or so.

5:40 p.m. update: It’s beginning to look and sound a lot like spring out there. Lightning and thunder are pushing through the area along with small hail and the potential for damaging winds.


Lightning in the area as of 5:40 p.m. (http://www.lightningmaps.org/realtime)

5:32 p.m. update: Severe thunderstorm warning issued for entire immediate D.C. area through 6:15 p.m. Wind gusts around 60 mph possible along with torrential rain.

5:30 p.m. update: Radar shows nasty line of storms, which may be severe and/or be warned for tornadoes, rapidly approaching the Beltway. Should reach the District by 6 p.m. and exit the Beltway around 7 p.m.

Radar at 5:30 p.m. (Weather Underground)
Radar at 5:30 p.m. (Weather Underground)

5:20 p.m. update: National Weather Service reports a funnel cloud was reported northwest of Fredericksburg. This storm is moving northeast right up I-95. Seek shelter.

5:16 p.m. update: TORNADO WARNING for Fredericksburg, much of Stafford, and eastern Prince William counties through 6 p.m. Warning includes Dumfries and Woodbridge and a large section of I-95. Radar detected possible tornado near Fredericksburg moving northeast at 55 mph. Take cover at lowest level of building in interior room if in the path.

5:14 p.m. update: Storms are roughly 30-45 minutes from moving inside the Beltway. Please take that into consideration for your commute. Get home NOW if you can make it in next 20 minutes (factoring in traffic) or, better, wait these out!

5:05 p.m. update: Radar at 5:00 p.m. shows a nasty line of storms moving towards the immediate D.C. area. Tornado warnings, in our far southern and southwestern areas are outlined in red polygons and severe thunderstorms warnings to our west and northwest are in yellow.

4:58 p.m. update: A tornado warning has been issued for our far southern and southwest suburbs, including Fredericksburg through 5:15 p.m. Take cover immediately if you’re in this zone below, which includes sections of Orange, Spotsylvania, Culpeper, Stafford and Fauquier counties:

4:52 p.m. update: The line of intense storms is coming into the metro region. A severe thunderstorm warning has been issued for D.C.’s far north and west suburbs including Frederick, Leesburg, and Gaithersburg through 5:30 p.m. Torrential rains and wind gusts to 60 mph or so possible with this storm

4:38 p.m. update: The National Weather Service has just issued a special statement urging caution due a to “rush hour tornado threat”

rush-hour-tornado-threat

4:35 p.m. update: Here’s a radar snapshot from 4:30 p.m. showing the intense line of storms headed into the region, which includes active tornado warnings in central Virginia. One (hopefully) mitigating factor for tornadoes in the immediate D.C. area is relatively low levels of atmospheric instability, but we still cannot rule out a tornado or two in the region when this comes through the immediate area between about 5:30 and 7:30 p.m.

Radar snapshot 4:30 p.m. (Weather Underground)
Radar snapshot 4:30 p.m. (Weather Underground)

4:20 p.m. update: If you can avoid commuting between about 5:30 and 7:30 p.m. tonight in the immediate metro area, try to do so.  That’s when heavy rain is very likely along with the chance of very strong winds and a tornado or two in the region.


HRRR model simulated radar at 6 p.m. (WeatherBell.com)

4:12 p.m. update: A preliminary report indicates two people died in a tornado in Waverly, Va., between Petersburg and Norfolk.

4:00 p.m. update: The line of thunderstorms currently entering central Virginia is of particular concern for the D.C. metro region starting around 5 p.m. from southwest to northeast. There are multiple active tornado warnings with this line and it is quite possible it will trigger tornado warnings in the D.C. area as it comes through.

(NWS)
(NWS)

3:50 p.m. update: Numerous tornado warnings have been issued and are active in southeast and central Virginia and in North Carolina, including in Chapel Hill, Newport News and Norfolk. You can follow the latest tornado warnings at the Twitter feed: @NWStornado

3:25 p.m. update: A tornado watch has been posted for the entire D.C. metro region through 11 p.m.

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

A tornado watch means conditions are favorable for tornadoes to develop, but not guaranteed and you should stay alert.   A tornado warning, on the other hand, means a tornado has been detected by radar or spotted by an eyewitness, and you should take cover in an interior room at the lowest level of your building, immediately.

Original post from 12:18 p.m.

A rare mix of  ingredients may gel for severe winter thunderstorms across the D.C. area, particularly late this afternoon and this evening.

storms_02

Damaging wind gusts, very heavy rain and even isolated tornadoes are possible in thunderstorms that develop.  These hazardous storms could impact the afternoon-evening commute.

We stress that dangerous storms are possible, but not guaranteed. Some areas may get hit hard, while others just see ordinary showery weather. Generally, the greatest risk of severe weather is south and southeast of the metro region, where temperatures surging to near 70 degrees offer fuel for developing storms.


(NWS Storm Prediction Center)

The National Weather Service Storm Prediction Center has placed the D.C. area in its “enhanced risk” zone for severe thunderstorms, which is level three on its one to five scale.

The Storm Prediction Center indicates there is a 30 percent chance of damaging winds within 25 miles of a point in the region, and 10-15 percent chance of tornadoes. A stronger tornado cannot be ruled (at least EF2 on the 0-5 scale), but is most likely south of the D.C. area.

Technical discussion

The crux of the entire severe weather forecast today revolves around how much the atmosphere will destabilize this afternoon and evening. Exceptionally strong wind shear is in place. We are monitoring the movement of a coastal front north and east. A surge of unseasonably mild air is expected to invade the D.C. region but the high resolution models (NAM-4 km and HRRR-3 km) disagree with regard to the magnitude of the warm-up.


NAM-4 km forecast of surface temps, valid 2 pm. (WeatherBell.com)

HRRR-3 km forecast of surface temps, valid 4 p.m. WeatherBell.com

The NAM pushes D.C. over 60 F by 2 p.m., and the HRRR is close behind, by about 2:30 p.m. The NAM brings us up to 65 degrees approaching sunset, holding it here for a couple hours afterward. The HRRR rapidly ramps up the temp at 68 degrees at 4 p.m. – due to breaks in the afternoon cloud cover – then sustains temps at 65 until about 8-9 p.m. The latest SREFs (fine scale ensemble runs) peak at 63 degrees late in the afternoon.

Thus, it seems the preponderance of model data is quite aggressive in a vigorous warm-up. A glance at the regional surface temperatures (shown below) reveals the D.C. region, as of 11 a.m., is locked in the mid-upper 40s. But a very strong temperature gradient is just on our doorstep, to the southeast, and temps are expected to begin rising quickly through the afternoon, from southeast to northwest.


Regional temperature analysis. Brown lines are isotherms. At 11 a.m., D.C. proper sits close to 50 degrees.

Next, we look at a measure of instability, or CAPE (convective available potential energy). The higher the CAPE value, the more likely we will experience thunderstorms.

There is a mix of values suggested by the various high resolution models. The NAM-4km builds in highest CAPE during a brief period of time, from about 4-9 p.m. The largest values lie to our south, across east central Va., but higher values do creep into northern Virginia and lower southern Maryland around sunset.


NAM-4 km CAPE, valid 6 p.m. (WeatherBell.com)

The HRRR-3 km builds in a plume of much higher values area-wide by 4 p.m., but the largest values still lie to the south of D.C. Elevated CAPE hangs around area-wide until 9-10 p.m.


HRRR-3 km CAPE, valid 4 p.m. (WeatherBell.com)

It’s worth noting that the ensemble forecast (SREFS) lies closer to the NAM-4 km in terms of amount of available instability, which is generally half of what the HRRR portrays.

What do the simulated radar fields show? The HRRR pushes a broken convective line, with intense cells, through the region between 4-6 p.m, coincident with the aggressive and early rise in CAPE. Only scattered showers remain through the evening.


HRRR-3 km simulated radar reflectivity, valid 5 p.m. (WeatherBell.com)

The NAM-4 km also suggests a broken line will move through but later, 6-8 p.m, with the strongest cells to the south of the District.


HRRR-3 km simulated radar reflectivity, valid 7 p.m. (WeatherBell.com)

Interpreting the various sets of guidance, it seems that we can expect a period of rapid atmospheric destabilization after mid-afternoon, peaking around sunset. The magnitude of the destabilization is more uncertain. In spite of heavy overcast, moderate showers and resistant cool air (due to cold air damming), it is hard to ignore the model guidance. The HRRR is perhaps overdone with the intensity of low-level warming and magnitude of instability.

Consistent with the Storm Prediction Center’s thinking, we believe the greatest severe threat still remains to the south of the District. Temperatures will likely break into the low 60s by sunset. The prospect for strong and perhaps locally damaging thunderstorms in our region, between the hours of 4-8 p.m, is reasonable. T

The greatest threat is damaging wind gusts; gusts to 40-50 would be more common, with isolated values in the 60-70 mph range – although the likelihood for something this extreme increases south of D.C. proper.

Additionally, the amount of potential, low-level spin (helicity) due to wind shear is very high across much of the eastern Mid Atlantic. This does not necessarily portent strong, long-track tornadoes, but isolated spin-ups associated with linear as opposed to supercell-type convection.

Older updates

3:20 p.m. update: A tornado watch will be posted for the D.C. area shortly according to the National Weather Service.

2:20 p.m. update:  Flash flooding may end up being the hazard that impacts more people than any of the others through this evening, including damaging winds or tornadoes.  The National Weather Service has issued a special statement highlighting the flash flood potential, stating rainfall rates of 1-1.5 inches per hour are possible with storms moving through.

(NWS)
(NWS)

The most likely timing for heavy storms is between roughly 5 and 8 p.m. from west to east.

Due to all the recent rain, the ground is close to saturation.  Streams, creeks and poor drainage areas will be susceptible to flash flooding this evening.


HRRR storm simulation between 5 and 8 p.m. this evening. (WeatherBell.com)

1:45 p.m. update: A tornado watch has been issued for central and eastern Virginia, and southeast Maryland and is in effect through 9 p.m. The watch may well be expanded northward to cover the D.C. area or a new watch issued.

1:25 p.m. update: The National Weather Service Storm Prediction Center – in a special discussion – says it is likely (95 percent chance) to issue a tornado watch for areas from the District south, in the coming hours.

(NWS SPC)
(NWS SPC)

It notes there is the potential for “a couple” strong tornadoes, rated EF2 or higher on the one to five scale.  “It seems very likely that the tornado risk will continue to increase/shift generally northward this afternoon,” it cautions.

Capital Weather Gang’s Ian Livingston contributed to this post.