7:30 p.m. — Storms have weakened and are no longer severe. Updated forecast through Wednesday.

After putting down hail as large as ping pong balls and unleashing wind gusts up to 60 mph in parts of the region (see earlier updates), storms have substantially weakened over the last 60 to 90 minutes. Radar shows some showers still scattered showers with locally heavy rain and even some lightning around the region, but they should gradually diminish or move off over the next hour or two.

Here’s the forecast for the rest of tonight and tomorrow:

Tonight: Once the storms are totally out of the region, it’s fairly quiet overnight as skies remain partly cloudy. Lots of low-level humidity and little wind may equal some fog in the favored locations. Lows range from near 70 to the mid-70s.

Tomorrow: It’s yet another hot day, much like the ones that came before it. Under hazy sunshine, highs again rise to a range from near 90 to perhaps as high as the mid-90s. Although temperatures step back a notch or two compared to today, humidity remains high so we’re still talking heat indexes near 100. Some afternoon showers and storms are possible as well.

Unless any severe weather develops, this is the final update in this post.

6:25 p.m. — Intense storms over Dale City and between Middleburg and northern Loudoun County. A weakening trend elsewhere.

The showers and storms inside the Beltway and to the northeast have generally weakened and are no longer severe. However, we see an intense storm between Dale City and Burke, which may produce damaging winds and ping-pong ball size hail, and another to the northwest between Middleburg and Purcellville, pushing east-northeast toward Leesburg. Severe thunderstorm warnings are in effect for both of these storms, which are moving east at around 15 mph, until 7 p.m.

After 7 p.m., showers and storms may continue to affect parts of the region and, while an isolated storm could continue to be severe, we expect their intensity to generally weaken.

6:05 p.m. — Storms scattered around the Washington region, some still severe

The storm over the District and just to its southeast, which produced damaging winds and large hail, is no longer severe. However, we see severe storms southwest of Leesburg, in southwest Fairfax County between Lake Ridge and Burke and then on the northeast side of Columbia.

Any of these storms could produce some pockets of damaging wind and hail, in addition to heavy rain and frequent lightning.

5:55 p.m. — Large hail reported on the Mall, Capitol Hill

The severe storm over the southern half of the District has produced some hail between half-dollar and perhaps golf ball size. We received a report of half-dollar size hail on the Mall and these images of hail just to the south:

5:45 p.m. — Video shows pedestrians struggling with the torrents in downtown Washington

5:30 p.m. — Strong to severe storms from Centreville to Great Falls, near north Bethesda, and from downtown Washington southeast to Upper Marlboro

Many parts of the Washington region are dealing with intense storms producing heavy, possibly flooding, rain, frequent lightning, strong winds, and hail.

We have severe thunderstorm warnings in effect for the northern half of Fairfax County, from Centreville to Great Falls, around north Bethesda near the Interstate 270 spur in Montgomery County, and from downtown Washington southeast to Upper Marlboro in Prince George’s County. The warnings expire between 6 and 6:15 p.m.

These storms are slow-movers (drifting east around 5 mph), meaning they could easily produce 1 to 3 inches of rain, and some places have already reported over an inch.

5:15 p.m — Flood warning for District; 58 mph wind gust reported at Andrews Air Force Base along with half-dollar size hail

The National Weather Service says up to an inch of rain has already fallen from the storm over the District and more could fall causing flash flooding. A flood warning is in effect until 8 p.m.

The image above shows high water adjacent to Adams Mill Road in northwest Washington.

Meanwhile, Andrews Air Force Base has clocked a wind gust of 58 mph and reported half-dollar sized hail.

5:00 p.m. — Three severe storms in Washington region: near Chantilly, northeast Washington and Andrews Air Force Base

In the last 45 minutes, three vigorous storms have erupted in the Washington region, each of them producing heavy rain, frequent lightning, strong winds and some hail. Warnings are up for storms between Chantilly and Reston, the northeast District, Takoma Park, College Park, and Beltsville and right over Andrews Air Force Base.

These storms are slow-movers, only drifting east-northeast around 5 mph, which will allow them to produce very heavy rainfall. Try to avoid driving through these storms if possible.

Here are some images of the storms and their effects:

4:45 p.m. — Severe thunderstorm warning for City of Fairfax, northwestern Fairfax County, north central Prince William County in Virginia until 5:30 p.m.

A severe thunderstorm was located over Chantilly, moving slowly east at 5 mph, dropping heavy rain, small hail, and producing vivid, frequent lightning.

4:40 p.m. — Severe thunderstorm warning for D.C., Silver Spring, Arlingon Va. until 5:15 p.m.

This storm developed quickly over DC and is producing frequent cloud-to-ground lightning, heavy rain, and strong winds.

3:10 p.m. — Severe thunderstorm watch issued for entire D.C. and Baltimore region until 9 p.m.

Storms are increasing in eastern West Virginia and are about to move into Virginia, while a couple of isolated storms have popped up in the immediate area. Given the possibility of strong to severe storms in our region through this evening, the National Weather Service has issued a severe thunderstorm watch until 9 p.m.

A watch means conditions are conducive for some storms to become severe, and residents should remain alert. It means severe weather is possible but not assured.

However, if a severe thunderstorm warning is issued for your location, it means a severe storm is imminent and you should seek shelter.

Original post from 3 p.m.

Given the hot and humid air mass of the past several days, thunderstorms popping up here and there have been a daily occurrence. This morning, prospects for general, late day storms appeared no different. However, the National Weather Service Storm Prediction Center early this afternoon upped the ante a bit, upgrading the risk of severe thunderstorms from marginal (level 1 out of 5) to slight (2 out of 5) in the greater D.C. region.


(National Weather Service Storm Prediction Center)

Isolated storms were already popping up in the region this afternoon but are expected to become somewhat more numerous, especially around 5 to 9 p.m. Any storms that develop could produce very heavy rain, frequent lightning, strong winds and hail.

Like the past two nights, we can’t rule out some storms lingering after dark until 10 or 11 p.m.

Storm dashboard


x (The Washington Post/The Washington Post)

Approximate arrival time: 5 to 9 p.m., generally earliest west and latest east; but storms could pop up during the window throughout this time window anywhere

More isolated storms could pop up in the early and midafternoon hours

All clear: Around midnight

Storm duration: 30 to 45 minutes

Chance of measurable rainfall in any location: 40 percent.

Storm motion: west to east

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

Possible storm effects: damaging winds, hail

Rainfall potential: Highly variable. Locally up to 1 to 2 inches.

Discussion

The very small patch of elevated severe thunderstorm risk encompassing our region requires explanation. We are tracking a small disturbance in the middle atmosphere approaching from West Virginia. It’s a vortex in the flow and like an eddy in a stream, and it will drift over our realm by evening. It’s had a history of organizing a small cluster of thunderstorms. It may serve to trigger a batch of strong to severe storms east of the Blue Ridge.

This storm cluster is shown in satellite imagery below. It’s not unlike the circulation feature behind Sunday night’s super-electrified thunderstorms that impacted several counties in Central Maryland.


Early afternoon satellite imagery. (NOAA)

Our concern is the arrival of this system during the late afternoon and early evening, when the atmosphere will be most unstable.

The high resolution forecast models differ a bit in terms of storm coverage for later today, and it’s unclear if they are able to completely resolve the small circulation approaching the region. One of the model predictions below, for 8 p.m., shows a complex of storms just west and northwest of the Beltway.


High-resolution NAM simulated radar at 8 p.m.

Late-day thunderstorms may also trigger independently of the vortex, such as along the ridgelines, or along the bay breeze front, or even in connection with the urban heat islands of Baltimore and Washington. So general “pop-ups” may happen anywhere, at any time.

The wind shear (increase in winds with altitude) today is extremely weak, and in fact virtually nonexistent. These types of storms, called “pulse storms,” erupt and decay rapidly, but may spend 10 to 15 minutes in a strong to severe phase. Given a very unstable air mass, such storms can briefly generate very intense lightning, torrential downpours and microbursts (localized, fan-shaped blasts of damaging wind).

If the vortex crossing the mountains weakens, today’s storms will stay isolated and short-lived. But if the circulation remains intense and taps the building instability east of the mountains, a more coherent cluster of longer-lived storms may ensue … upping the odds that more people will experience the types of strong to severe weather mentioned above.