3:40 p.m. – Tornado watch canceled in the city and west
With the line of storms now approaching the bay, the tornado watch has been ended for much of the immediate area. Once the last storms exit into the bay the severe weather threat will be over for the entire region. Behind those storms, showers continue to diminish over the next hour to two.
Good news for evening plans is that this is all exiting on the early side. The Nationals game should also happen without much weather worry.
3:25 p.m. – Strongest storms shifting east
The latest severe thunderstorm warning is up for a big chunk of our east and southeast suburbs until 4:30 p.m. The threat is primarily for the risk of damaging wind.
Storms are now mainly east of Interstate 95, although some moderate to heavy rain lingers to the west. This is all moving about an hour quicker than anticipated on the back end it seems. As such, we should see rain significantly winding down into the immediate area before the heart of the commute.
3:05 p.m. – Strong to severe storms focused near Interstate 95
Front-running storms have tended to become the dominant ones over the last half hour or so. That may mean this is all moving on the fast side compared to original expectations. The latest round of warnings has been issued for southern and northeastern suburbs until 3:45 p.m., mainly for damaging wind potential.
See bottom for earlier updates…
Original post from 12:45 p.m., timeline since updated
Much as we did last Friday, we’re eyeing the risk for heavy showers and storms to erupt and move through the region this afternoon into early evening.
Hit-or-miss showers are possible at just about anytime before that, but the main risk for intense or damaging storms arises out west during the early-to-mid afternoon, then shifts east and eventually out of the area in the early evening.
The primary risks from what should be a line or lines of storms are heavy rain, lightning and the threat for damaging winds over 60 mph in some locations. A tornado or two can’t be ruled out, although they would probably be brief and weak if any do occur.
Approximate arrival time for storms:
- 2 p.m. in the west, 3-4 p.m. in the east.
- Showers, some heavy, possible from early afternoon until around sunset.
All clear: Early evening.
Storm duration: 30 to 45 minutes, longer if multiple storms.
Chance of measurable rainfall in any location: 80 percent.
Storm motion: West to east as a line, with individual storms moving more northeast.
Likely storm effects: Heavy rain, gusty winds, lightning.
Possible storm effects: Isolated damaging wind gusts, a brief tornado.
Rainfall potential: 0.25 to 0.75 inches but variable. Some places could receive up to one inch.
Severe storm discussion
As with events on April 14 and 19, a strengthening and dynamic jet stream is freshening the winds over our region, setting the stage for a severe weather event this afternoon into evening.
Like in those recent events, we lack a strongly unstable atmosphere, thanks to layers of thick cloud that have impeded heating of the ground. But it should be just enough juice to kick off widespread storms. A question on wind damage potential, in particular, is whether it will be on a fully isolated basis or somewhat more widespread.
Although clouds dominated the morning, a southerly wind has pushed the thickest cloud-cover, associated with a warm front, north of the immediate area during the midday. At least periodic sunshine is likely into midafternoon.
A convective line of showers and thunderstorms that will sweep through our region between 2 and 5 p.m. is now forming to our west, ahead of a cold front. The region will have a brief window to destabilize before that line arrives, which may limit storm organization somewhat.
Nevertheless, the increase of winds with altitude (called wind shear) makes us concerned about the prospects of severe storms, because the shear is very intense and can lead to a few strong, well-organized, long-lived thunderstorm cells.
Areas of particular interest may be along segments that try to “bow” as they move east. Those bows can increase wind damage potential when they happen.
Accordingly, the NOAA Storm Prediction Center (SPC) has mapped parts of our region in an enhanced risk report, mainly for the afternoon. An enhanced risk is Level 3 out of 5 in terms of the widespread, severe threat. Areas west of Interstate 95 are generally in a slight risk, which is one category lower.
The high resolution models are portraying a storm line, possibly broken, affecting our region as early as 1 p.m. well west, and traversing the D.C. region mainly between 2 and 5 p.m.
The very strong wind shear will generate some rotation potential in these storms, perhaps resulting in a weak tornado or two. These spinners most typically initiate along the wavy, front edge of convective lines but may also develop in any lone cells that form out ahead of the main line.
We note that the atmosphere appears to be destabilizing most rapidly to the south and east of Washington. Because of this, the greatest threat of damaging winds and tornadoes may include southern Maryland, the Delmarva, and central and southeast Virginia.
It is likely that the National Weather Service will issue a tornado or severe thunderstorm watch for parts of our region this afternoon. A watch indicates that conditions are favorable for severe weather. Warnings are later issued as storms occur.
We will continue to update as the situation unfolds.
2:43 p.m. – Tornado warning parts of Montgomery and Fairfax counties
A tornado warning is up for areas in red below, including Potomac, Rockville, and Olney. This is through 3:15 p.m. Seek shelter in this area. There is also another severe thunderstorm warning for northern parts of the area, for strong winds.
2:25 p.m. – Strong to severe storms overtaking much of the area
Storms out ahead of the main line have now been warned for the potential of damaging wind gusts. A warning that runs until 3:15 p.m. includes much of the immediate area.
And a severe thunderstorm warning has been issued for a big chunk of the western half of the area. It includes parts of Montgomery, Loudoun, and Fairfax counties until 3:00 p.m. Damaging winds to 60 mph are the main threat from these storms.
1:55 p.m. – Severe storms into far southwest parts of the area
A severe thunderstorm warning is up for parts of Fauquier and Prince William counties until 2:30 p.m. Additional warnings for western parts of the area are possible in the near term. The main risk from these storms is damaging wind.
1:40 p.m. – Tornado watch issued as storms develop west
A tornado watch has been issued for our area. In addition to covering parts of Virginia, Maryland and the entire District, it also includes parts of Delaware, New Jersey, and Pennsylvania. The watch runs until 9 p.m. this evening.
A line of storms is now developing to our west and southwest. It will be affecting southwest and west parts of the area over the next hour. Additional storms are trying to fire up ahead of the line, so they will need to be watched, as well.