* Flash flood watch until 5 a.m. *


Radar courtesy MyRadar | © OpenStreetMap contributors

1:45 a.m. — Torrential rain, flooding continues across region...may continue into the predawn hours

Storms have defied forecasts and regenerated and regenerated resulting in the National Weather Service extending the flash flood watch until 5 a.m., while flash flood warnings are in effect for many areas east and southeast of the Beltway. In some of these areas 5 to 7 inches of rain have fallen and another inch or two is possible.

At 1:45 a.m., radar showed storms along a corridor from Leesburg to Great Falls to Bethesda to the District then curling to the southeast into Southern Maryland. Many of these storms are training or passing over the same areas repeatedly, leading to flooding.

It may still be a few hours until these storms finally dissipate and move off and it’s possible flooding will expand into some areas around the District and to the west and northwest where it has been raining very heavily the last couple of hours.

11:20 p.m. — Flash flooding a concern east and southeast of D.C. as storms continue across much of the D.C. area

A flash flood warning remains in effect for much of the area until midnight with a trio of flash flood warnings (green boxes below) across the eastern and southeastern suburbs of D.C., where up to 3 to 5+ inches of rain has fallen with more to come. Driving conditions are dangerous in these areas, so take extreme caution if you have to be out. Storms may linger in these and other parts of the DMV--in fact, new storms are popping up inside and west of the Beltway now--a few more hours before finally dissipating.

10:40 p.m. — Stubborn storms won’t quit over eastern half of D.C. area

Raging thunderstorms continue to dump heavy amounts of rain across the eastern half of the D.C. area, east to the Chesapeake Bay and south into lower Southern Maryland, with a severe thunderstorm warning until 11 p.m. across a large swath of Southern Maryland including St. Charles, La Plata, Hughesville, Eagle Harbor and Golden Beach. These storms may continue redeveloping over the same areas a couple of more hours.

The storms, which began during the late afternoon and have lasted well into the evening, have brought several trees down according to Pepco with nearly 9,000 customers affected by outages at this time. High water may have contributed to a jeep flipping over in Montgomery County and prompted water rescues in Prince George’s County.

9:40 p.m. — Heavy storms hanging on south and southeast of D.C.

Storms won’t quit south and southeast of the Beltway, extending eastward through southern Prince George’s County and northern Clavert County to the Chesapeake Bay. A severe thunderstorm warning remains in effect until 10 p.m. for a large portion of that area (yellow box) with damaging wind gusts and small hail possible. A flash flood warning is in effect until 12:30 a.m. for areas including Clinton, Andrews Air Force Base, Upper Marlboro and Largo. Some areas in this zone have seen 3 to 4 inches of rain this evening.

8:10 p.m. — Severe storms lingering east and southeast of D.C.

One severe thunderstorm warning remains in effect--for central Prince George’s County including Largo, Andrews Air Force Base and Upper Marlboro until 8:30 p.m.--as the late-afternoon and evening storms finally start to dissipate and exit to our east.

Pockets of heavy rain, lightning and gusty winds will linger in east-central Prince George’s County, southern Anne Arundel County, and northern Calvert County for the next hour or so, as well as northeast of D.C. from around Columbia to Glen Burnie and into the Baltimore area.

7:25 p.m. — Severe storms with damaging winds showing signs of eventually exiting to the east

Intense storms with heavy rain, frequently lightning and wind gusts near 60 mph have brought trees down as they continue to move through southern Montgomery County, D.C., southern Prince George’s County and points east.

While a severe thunderstorm warning remains in effect until 7:45 p.m. for a large area east of D.C. and south of Route 50, where we suggest staying inside and delaying travel for now, the storms should begin to exit to the east during the net hour or so, and may weaken as they do so.

6:40 p.m. — Storms focused around and east of the Beltway; some with damaging winds possible

Storms have intensified around and east of the Beltway with multiple severe warnings in effect (see yellow boxes below). A 60 mph wind gust has been reported at Reagan National Airport, which meets the criteria for severe winds.

6:05 p.m. — Storms with very heavy rain from Bethesda to Severna Park; Damaging wind gusts possible north and east of the city, where flood threat could develop

Storms have greatly increased in coverage and intensity over the last year mainly north of downtown Washington along the northern side of the Beltway and then continuing east just north of Rt. 50. These storms are producing a good deal of lightning and very heavy rainfall.

Storms just northeast of Bethesda have become potentially severe and could produce some damaging gusts as they pass through southeastern Montgomery County over the next 40 minutes.

The storms east of the Beltway are the most intense and could unleash brief bursts of damaging winds. A severe thunderstorm warning is up for a large area north of Rt. 50 through 6:45 p.m.

As the storms are organized along a west to east line and may pass over the same areas repeatedly, we’ll have to watch for the possibility of flooding - especially if new storms form and continue tracking across the corridor.

5:10 p.m. — Storms beginning to develop, may flare up quickly next hour

Radar is beginning to show some small, but growing storm cells near the Interstate 95 corridor. They are widely scattered but - assuming they increase in size - should cover more territory especially as they drift east of the Interstate.

The National Weather Service Storm Prediction Center issued a statement noting the atmosphere east of I-95 is strongly unstable, which means there is some potential for storms to erupt and become severe.

3:45 p.m. — Radar is quiet in the Washington region

While severe storms are bombarding southeast Pennsylvania and southern New Jersey, little has yet to erupt in the Washington and Baltimore region.

Our short-term models do suggest storms may start to flare-up, especially after 5 or 6 p.m. The most likely area to see storms will be along and east of Interstate 95, but a storm could pop-up anywhere in the region.

Original article from 2:45 p.m.

A hot, unstable air mass over the Washington and Baltimore region has set the stage for numerous strong to severe thunderstorms this afternoon and evening. The storms may be hit or miss, but they could erupt quickly with little notice and unleash bursts of damaging winds and hail.

The National Weather Service has issued a severe thunderstorm watch for much of the northern Mid-Atlantic until 11 p.m. Monday night, extending through Washington and Baltimore to eastern Pennsylvania and all of New Jersey.

A storm watch means conditions are conducive to the development of storms and you should stay alert. If a storm warning is subsequently issued, it means a storm is imminent or beginning, and you should seek shelter indoors.

A flash flood watch is also up for much of the Washington and Baltimore area, the summertime moisture set to brew slow-moving downpours that could drop one to three inches of rain in a hurry.

The storms come less than 24 hours after a severe thunderstorm injured 19 people in Anne Arundel County on Sunday evening; violent winds toppled a tree onto a garage where guests at a child’s birthday party were sheltered.

Storms at a glance

Timing: Storms look to fire along and west of Interstate 81 as early as 3 p.m., with thunderstorms bubbling up in the D.C. to Baltimore corridor by 4 or 5 p.m.

Individual storms should last an hour or less, but some places — especially near and east of the District — could see multiple waves of thunderstorms. Areas to the west should see their storms wind down by mid evening, though thunderstorms may linger in eastern zones until after sunset

Impacts: Strong to locally damaging winds could accompany any storms that develop, along with hail to the size of quarters or perhaps a little larger in the most intense cores. Frequent lightning will also be a threat with any storms.

Thunderstorms will develop and collapse quickly due to their pulse-type nature, so it won’t take long for any towering clouds to begin spitting out lightning strikes.

Flash flood risk: The slow-moving storms may eventually move into clusters capable of producing torrential downpours, with rainfall rates briefly topping three inches per hour. A few locations could see a quick 1 to 3 inches of rain if storms stall.

Discussion

A toasty summer air mass in place juxtaposed against cool air at high altitudes has left the atmosphere highly unstable, offering storms plenty of fuel to work with. As the lower atmosphere warms in the midafternoon sun, a spattering of storms will quickly bubble up. Satellite imagery already revealed building clouds — the precursor to thunderstorm development — east of the Blue Ridge around 2 p.m. as strong storms quickly fired in New Jersey.

“Today, like Sunday, the atmosphere will become exceedingly unstable, with isolated, rapid development of severe thunderstorms,” wrote Jeff Halverson, Capital Weather Gang’s severe weather expert. “Given the tremendous buoyancy for strong updrafts, expect isolated to scattered instances of large hail, damaging winds, intense lightning and torrential downpours. Storms may once again be particularly intense along and near the Bay.”

Slightly lacking today are winds at the mid-levels, which means there won’t be much to move storms along. Any thunderstorms that occur will eventually rain themselves out, their cores collapsing — perhaps accompanied with strong or damaging wind gusts — after a little while. The quick pulse nature of storms today makes predicting them especially challenging, making it all the more important to seek shelter if a warning is issued.

Storms will likely be strongest and most numerous just to the west of the Chesapeake Bay, where an onshore “bay breeze” could give storms a boundary to develop on. There are some indications storms may cluster along that boundary and survive into the evening even after the sun has begun to set.