4:50 p.m. — Flash flood warning for Bethesda, northern District, Silver Spring
Thunderstorms with torrential rain are moving over the northern part of the District and southern Montgomery County, prompting a flash flood warning.
“Between 0.5 and 1 inch of rain has fallen,” the Weather Service writes. “The expected rainfall rate is 1.5 to 2.5 inches in 1 hour. Additional rainfall amounts of 1 to 2 inches are possible in the warned area.”
The Weather Service warns the flooding could be “life-threatening.” Avoid traveling near streams that could quickly overflow and poor drainage areas. If you encounter a flooded road, turn around — the water level is difficult to judge.
4:30 p.m. — Severe thunderstorm warning for downtown Washington and its northern suburbs through 5 p.m.
An intense thunderstorm stretching from near Glen Burnie, Md. to Bethesda is pushing east and southeast. It has prompted severe thunderstorm warnings for the District and most of its northern suburbs.
The most intense part of the cell is near Silver Spring where some small hail has been reported. Otherwise, its main impacts will be some strong bursts of wind, heavy downpours and lightning as it progresses through the northern half of the District, northern and central Prince George’s County and eventually Anne Arundel County.
3:55 p.m. — Storm in Montgomery County could produce 60-70 mph winds, one-inch hail; flooding rain possible in southern Fairfax County
A severe storm that is now moving through western Montgomery County has a history of producing hail of 1-1.25 inches in diameter in both Leesburg and Poolesville. It is also unleashing very strong winds — possibly as high as 60-70 mph. The associated severe thunderstorm warning has been extended east through the I-270 corridor into eastern Montgomery County, until 4:30 p.m., including Potomac, Rockville and Olney.
Here are some images of the storm:
Meanwhile, in southern Fairfax County, a flash flood warning is in effect in Burke, Springfield and Alexandria due to torrential rainfall rates of up to 1.5 to 2.5 inches per hour. This rain should relent over the next 30 to 45 minutes but could cause streams to overflow and flooding of poor drainage areas. Don’t try to cross a flooded road in your car; turn around, don’t drown.
3:30 p.m. — Intense storm with hail near Annapolis, with severe storms also developing to the west
The most intense storm at the moment is in central Anne Arundel County, including Annapolis, where there’s a severe thunderstorm warning in effect until 3:45 p.m. The warned storm has a history of producing hail up to 1-inch in diameter in Crofton.
Elsewhere, storms are widely scattered through the area but are increasing in intensity. Severe thunderstorm warnings have been issued for northern Loudoun and western Montgomery counties, including Leesburg, until 4:15 p.m. and for eastern Prince William and southern Fairfax County, including Manassas and Burke, until 4 p.m. Both of these storms could produce damaging wind gusts and hail, in addition to heavy rain and lightning.
2:30 p.m. — Scattered storms already erupting
Radar shows two thunderstorms have erupted inside the Beltway — one in Falls Church and Arlington and a second from southeast Washington to around Landover. Both are producing heavy downpours and some lightning. These will drift eastward through the District and along Rt. 50 in Maryland.
More numerous showers and storms are forming to the west near Interstate 81 which will also sweep through the metro area during the late afternoon hours.
No severe thunderstorm warnings have yet been issued but will become increasingly likely as we get into late afternoon and early evening when storms will have had the chance to mature.
2 p.m. — Severe thunderstorm watch issued until 9 p.m.
Due to the potential for intense storms into this evening, the National Weather Service has issued a severe thunderstorm watch for the entire D.C. area and over a region that spans from Richmond to Philadelphia.
Remember that a severe thunderstorm watch means ingredients are in place for possible severe storms; they are not a guarantee. 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 1:30 p.m.
Six days after intense thunderstorms erupted in the Washington region, including two tornadoes, another round is expected this afternoon and evening. Today’s storms could also be quite vigorous, with the potential to produce damaging gusts and hail in addition to heavy downpours and frequent lightning.
The tornado risk is lower compared to last Friday, but we cannot totally rule out a short-lived twister.
The storms are being fueled by hot, humid air ahead of a strong cold front advancing toward the area. Today will probably be the third day in a row topping 90 degrees before the storms expel the heat, making way for a beautiful stretch of weather Friday through the weekend.
The National Weather Service Storm Prediction Center has placed the region in a level 2 out of 5 risk zone for severe storms, which stretches from around Virginia Beach to Philadelphia.
Timing: Storms should initiate, mostly west of Interstate 95, between 2 and 4 p.m. Storms will probably be most numerous between 4 and 8 p.m., but could linger in some areas — especially south and east of Washington — through around 11 p.m. Rain should be over in most areas by around midnight or so.
Storm coverage and duration: Storms will be scattered but there may be multiple rounds increasing the chance most places see a storm at some point. Any individual storm may just last 20 to 40 minutes but some areas may be hit more than once.
Probable hazards: Heavy downpours, frequent lightning, gusty winds (30 to 50 mph).
Possible hazards: Damaging winds (50 to 70 mph), small hail
Small chance of: Violent winds (over 70 mph), large hail, tornado
Rainfall potential: Averaging around 0.5 inches, but localized totals over 2 inches possible.
The setup today features a volatile combination of an unstable air mass, abundant moisture, increasing winds with altitude, or shear, and several mechanisms to lift the air. The weather map for 2 p.m. is shown below.
On this map, you will note an approaching cold front with a weak low pressure system. Ahead of this front, in the soupy air is another area of low pressure. These two systems are expected to create considerable low-level convergence of air causing it to rise and fuel widespread thunderstorms through the afternoon and evening.
Storms may trigger as early as 2 p.m., especially in our western areas, and regenerate in the area over the following 5 to 6 hours.
The main form of organization suggested by the models is a multicellular mode — where larger, intense clusters develop, with some evolving into short arcs or lines.
Given the strengthening wind shear anticipated through the afternoon, a few cells may briefly acquire rotation, which increases the possibility of some larger hail and perhaps an isolated, weak tornado.
Severe thunderstorms warnings will probably be issued for damaging wind gusts in the 50 to 70 mph range. Lightning may be particularly intense in spots. Additionally, these cells will unload heavy downpours, and repeat passage could result in localized totals exceeding 2 inches in a short time.
The Weather Service’s Weather Prediction Center has placed the region in a marginal risk zone for excessive rainfall that could cause flooding — mainly near streams and areas with poor drainage.