Severe storms exit after blasting southern parts of metro area

As the severe storm passed through our eastern suburbs it continued to produce very strong winds and hail, as shown in the video below:

5:05 p.m. — Storm most intense in southern Prince George’s County, headed toward southern Anne Arundel and northern Calvert counties

The severe thunderstorm that raked parts of Prince William and southern Fairfax County, including Alexandria, is bolting toward the Chesapeake Bay. The most intense activity is currently near Dunkirk and is headed toward Deale and Chesapeake Beach. It likely contains hail and damaging bursts of wind. This area remains under a severe thunderstorm warning until 5:15 p.m.

4:50 p.m. — Multiple reports of downed trees in Lake Ridge area, including some on homes; lots of hail reports in Alexandria

In the Lake Ridge area of Prince William County, the Weather Service has received multiple reports of downed trees, including on homes, from an apparent downburst. As this same storm continued eastward, it produced widespread reports of hail in Alexandria, mostly pea size but there were a few reports of one-inch hail (quarter size).

4:40 p.m. — Reports of hail, and possible downburst around south Alexandria; Storm warning expanded east into Southern Maryland

As this large and intense thunderstorm cell has progressed through Prince William and Fairfax County, we’ve seen multiple reports of hail as well as some downed trees and limbs.

Radar shows the most intense activity from around Annandale to around south Alexandria, where estimated wind speeds are very high – upward of 60 mph around Ft. Belvoir.

The Weather Service has expanded the severe thunderstorm warning in effect (for eastern Fairfax County, the southern part of the District as well as western Prince George’s and western Charles counties) eastward through all of southern Prince George’s, northern Charles, southern Anne Arundel and northern Calvert counties until 5:15 p.m. 70 mph gusts and hail to the size of ping pong balls are possible.

This remains a dangerous storm.

4:10 p.m. — Storm warning extended into Arlington, Alexandria and D.C. (from downtown south) — 70 mph gusts, half-dollar size hail possible

A very intense storm is passing through Manassas and extends north to around South Riding and is moving into Centreville. A severe thunderstorm warning has been extended to cover much of central and southern Fairfax County, Arlington County, Alexandria and the southern half of the District, including downtown. Winds up to 70 mph and half-dollar size are possible as this passes. It’s moving west to east at 40 mph.

This is a dangerous storm. Seek shelter until it passes.

4:00 p.m. — Intense storm between Warrenton and Gainesville pointed at southern Fairfax County

A severe thunderstorm warning has been issued for central Fauquier, much of Prince William and southwest Fairfax County until 4:30 p.m. A rapidly intensifying storm could produce damaging wind gusts and hail as it progresses east at 35 — along and just south of I-66. Manassas and Centreville are in this storm’s path. After 4:30 p.m., it should head inside the Beltway.

3:45 p.m. — Severe thunderstorm watch issued until 9 p.m.

As storms continue to build southwest of Washington and are headed east-northeast, the National Weather Service has issued a severe thunderstorm watch until 9 p.m.

The watch indicates scattered instances of large hail, damaging wind gusts (up to 70 mph) and a tornado or two are possible in any storms that form.

Remember that a severe thunderstorm watch means conditions are conducive to intense storms, but not a guarantee. On the other hand, if a severe thunderstorm warning is issued for your location, it means a severe storm is imminent and you should seek shelter immediately.

While the watch is in effect until 9 p.m., we anticipate most of the storm activity will have cleared the D.C. region west of the Chesapeake Bay by around 7 p.m.

3:35 p.m. — Storms near Warrenton could expand north, but nothing severe at the moment

Despite twice indicating an 80 percent chance of issuing a severe thunderstorm watch, the National Weather Service has yet to issue one as storms have been sparse and slow-developing.

There is one cell of interest around Warrenton and Haymarket which looks to track along and just south of I-66. It does contain lightning and heavy downpours and could intensity as it passes through Prince William and southern Fairfax County over the next hour or so. It could also expand north some.

We’ll keep you posted with any additional developments.

2:45 p.m. — Scattered late afternoon storms probable; severe storm watch anticipated

The midday showers threw a bit of a wrinkle in the forecast, shutting down the likelihood of multiple rounds of storms. Instead, we’re probably just looking at one round of scattered storms in the late afternoon and early evening hours as the cold front approaches.

The National Weather Service is likely (80 percent chance) to issue a severe thunderstorm watch shortly and we expect to see more storms popping up on radar as the front approaches.

These storms may be hit or miss (i.e. not everyone will see them) but some could well be severe. The sunshine we’ve seen since those midday showers has helped to destabilize the atmosphere.

“The strongest of these storms will be capable of damaging wind gusts and hail,” the Weather Service wrote.

Stay tuned for additional updates on any watch issued and storm developments.

Muggy air spreading over the Washington area will be met by a strong cold front Monday, setting off strong to severe thunderstorms. Storms could erupt in the area between midafternoon and early evening before drier and cooler air arrives overnight.

Storms will be scattered and probably most numerous and intense near and northeast of Interstate 95.

Severe storms, isolated tornadoes possible across Northeast today

“Damaging winds are the primary threat, but large hail and isolated tornadoes are possible as well,” the National Weather Service wrote. “The best chance for severe storms will be between 2 PM and 7 PM. An isolated instance of flooding is also possible.”

The storms may come through in two rounds, the first between around 2 and 4 p.m. and the second between 4 and 7 p.m.

The Weather Service’s Storm Prediction Center has placed much of our region in a level 3 out of 5 “enhanced” risk zone. Computer models, however, do indicate areas north and northeast of the Washington and Baltimore may see more ingredients come together for widespread severe weather.

Overall storm coverage: Scattered (hit or miss), most numerous along and east of I-95

• Interstate 81: 1 to 3 p.m.
• Germantown/Dulles/Warrenton: 2 to 3:30 p.m.
• Interstate 95 and Beltway area: 2:30 to 4 p.m.
• Southern Maryland to Annapolis: 3 to 4:30 p.m.

Estimated arrival time is for the first round of storms which may be widely scattered; a possible second round of storms may follow within an hour or two. Storms may be most numerous along and east of I-95 for second round.

All clear: 6 p.m. west of Interstate 95; 7 p.m. Beltway area; 8 p.m. Annapolis to Southern Maryland

• Significant (at least 4-in-10) chance of: Gusty winds (30 to 50 mph), downpours, lightning
• Medium (1-in-3) chance of: Damaging winds (50 to 65 mph), small hail.
• Small (1-in-10 or less) chance of: Brief tornado, large hail, destructive winds (over 65 mph), flooding.

Rainfall potential: Average 0.2 to 0.5 inches; locally amounts up to 1 inch or so possible.

A potent combination of an intensifying surface low pressure zone and very strong jet stream pattern aloft has heightened the risk for multiple rounds of strong to severe storms Monday afternoon, broadly across the Mid-Atlantic and Northeast.

The weather map (shown below) for 2 p.m. illustrates that the DMV is located in the warm sector of the low pressure region, meaning winds from the south will intensify and usher in warm and humid air. This will help destabilize the atmosphere Monday. A cold front advances across our region late in the afternoon, helping to trigger clusters and lines of storms.

The jet stream configuration (below) highlights an unusually vigorous trough, or southward dip, in the core of the jet, which will also be intensifying through the afternoon. A belt of very strong winds from the west will overspread the area and strengthen our wind shear, the increase in wind speed and turning of winds with altitude. The “dynamic uplift” caused by the advancing trough will work in concert with an unstable air mass to generate scattered to widespread thunderstorms.

We think the storms will come in two waves, with the initial batch moving into our near-western suburbs as early as 2 p.m. There are indications in the morning models that this first line of storms may be better organized and more intense, north of the Mason Dixon line. There, a severe thunderstorm watch is already in place, and the Storm Prediction Center believes the risk of wind damage may be as high as 45 percent (within 25 miles of any location) — an unusually high value for the Northeast.

Our threat of damaging straight-line wind is lower, at 30 percent, and the tornado threat is 5 percent. We may actually have a better shot at severe storms with the second wave, timed for 4 to 7 p.m. Model guidance suggests a line of intense cells will congeal right along I-95 in this time window. This will also buy the atmosphere a couple more hours to destabilize and for wind shear values to increase to even higher values.

However, the nature of storm cells in the second batch may be more scattered than widespread, and the most unstable air may lie over the Bay and further east. If storms from the first wave extend further south than the models suggest, then they may consume some of the energy building up for the second wave.

We were also socked in under a heavy overcast Monday morning, with showers already passing through. While this may break up a bit by early afternoon, the delay in the sun’s heating will reduce the time for the atmosphere to destabilize by several hours. Enough cold air moving in on winds aloft (associated with the trough), however, may compensate to some extent and keep the air moderately unstable.

We recommend staying weather-aware from 2 to 7 p.m. today. On radar, storms will organize into fast-moving, bowing line segments and clusters, with possibly a few embedded supercells or rotating thunderstorms.