This will be the last update for this article. Stay tuned for our PM update for the forecast for the rest of the evening through tomorrow, posting at 6:30 p.m.
4:50 p.m. — Storms sweep east and southeast of Beltway; intense storm approaching Fredericksburg
The storms are currently extending from near Annapolis southwest to Waldorf; they have largely left the District. While the storms contain very heavy rain, lots of lightning and strong winds, they are mostly below severe limits with wind gusts of 30 to 50 mph (over 58 mph).
The exception is towards southwest Charles County as well as the area just west of Fredericksburg where the storms are quite intense. In fact, storms about to enter Fredericksburg could unleash gusts of up to 70 mph.
These storms will continue to push east and southeast over the next hour, moving through southern Maryland and moving out of most locations around 6 p.m.
4:15 p.m. – Storms spread from Laurel to Quantico along I-95
A vigorous line of summer storms stretches from near South Laurel through the district, then south through Dale City to near Quantico. Some of the heaviest showers and strongest winds around Landover, just south of Burke and west of Triangle.
Earlier, winds blew at 67mph in Warrenton
All of this activity will cross Interstate 95 and emerge east of the Beltway over the next 30 minutes. The strongest storms may parallel Highway 50 in Maryland and also affect western portions of Charles County.
3:45 p.m. – Severe storm warning for downtown Washington and areas just north and east until 4:30 p.m.
Storms sweeping the interior of the Beltway are intense enough for a severe thunderstorm warning for southern Montgomery County, the District (from downtown areas northward) and northern and central Prince George’s County . In addition to torrential rain and lightning, some wind gusts could approach 60 mph in this area. The strongest winds are currently near Chevy Chase towards Silver Spring.
3:40 p.m. – Severe storms from Rockville to Manassas are closing in on the Beltway region
Severe storms with strong winds extend from Rockville to Reston to Centerville to Manassas to Nokesville from north to south. There are currently no warnings in effect for these storms, but they do contain lightning, very heavy rain and wind gusts likely in the range of 30-50 mph. They will move inside the ring road from northwest to southeast over the next 15 to 20 minutes and enter areas east of the ring road between approximately 4 and 4:15 p.m.
3:10 p.m. – Intense thunderstorms stretch from Germantown to Warrenton
The storms coalesced into a solid line from roughly Germantown, Maryland to Warrenton, Virginia. The strongest activity comes from sweeping areas east of Leesburg towards Poolesville where radar showed the potential for very strong gusts of wind; storms at the southern end of the line around Warrenton were showing signs of intensification, triggering a severe thunderstorm warning for central Fauquier County and western Prince William County until 3:45 p.m.
At their current travel speeds, the storms are expected to reach the Interstate 270 corridor between 3:15 and 3:30 p.m. and the ring road area and Interstate 95 around 3:45 and 4 p.m.
2:30 p.m. — Severe storm warning until 3:15 p.m. including Leesburg and Gaithersburg
Radar shows strong to severe storms around Frederick, Maryland, continuing southwest toward Purcellville in Loudoun County. Somewhat weaker storms are trailing southwest across northern Fauquier County. A severe thunderstorm warning covers northern Loudoun and western Montgomery counties until 3:15 p.m. This storm could produce wind gusts up to 60 mph and small hail as it sweeps east at 40 mph.
It appears that these storms will reach the Beltway area between approximately 3:30 p.m. and 4 p.m.
1:55 p.m. — Severe thunderstorm watch until 10 p.m.
As showers and thunderstorms reach the Interstate 81 corridor, the National Weather Service issued a severe thunderstorm watch for the Washington-Baltimore area until 10 p.m.; the watch also includes Roanoke, Richmond and Philadelphia – a combined population of over 20 million people.
“Destroying winds are the main danger,” the watch says, although torrential rains and lightning also pose a threat.
Remember that a severe thunderstorm watch means that conditions are favorable for severe thunderstorms, but it is not a guarantee. On the other hand, if a severe thunderstorm warning is issued for your location, it means that a dangerous storm is imminent and you should seek shelter immediately.
Original article from 1:30 p.m.
Monday will likely mark the eighth straight day with highs in the 90s in Washington, but a cold front breaking into the region will end that streak. This front will trigger widespread showers and storms as we move into this cooler air mass.
The strongest storms will pass quickly, arriving in our western regions around 2-3 p.m., all around the beltway around 3-4 p.m., and pushing into the Chesapeake Bay around 5 or 6 p.m. — although that timing may change slightly. There could be a weaker, trailing line of showers and thunderstorms closer to sunset that comes out at 10 or 11 p.m.
The afternoon series of thunderstorms could produce heavy showers, lightning and a few damaging gusty winds. The National Weather Service, which has placed the area under a Level 2 out of 5 severe weather hazard level, issued a bulletin saying it is “likely” (80% chance) to issue a thunderstorm watch violent.
A severe thunderstorm watch has already been issued for much of the northeast New York area to northern Maine through 8 p.m.
Storm potential Monday afternoon and evening is based on the arrival of a cold front from the northwest, crossing an unstable moist air mass along and ahead of it. The surface forecast graph below shows the position of the front at 8 p.m.:
During this time, in the middle atmosphere, a belt of strong winds will orient from Pennsylvania towards Maine, and, parallel to the front, will move towards the northeast.
Storms began to develop along the Appalachian Ridge to our west; these storms will then drift into Interstate 95 mid to late afternoon.
Given some sunshine and abundant humidity at lower elevations, we expect the atmosphere to destabilize to modest levels by mid-afternoon. This will energize and enlarge the updrafts of the clouds. However, heavy clouds drifting over the region from storms further northwest could prevent the atmosphere from reaching full destabilization on Monday afternoon.
With moderate instability, the degree of storm intensity and organization is determined by wind shear, which is the increase in wind speed with height. Wind shear levels measured by weather balloon Monday morning at Dulles Airport showed no exceptional levels, only about 20 mph (18 knots). With the faster wind ribbon approaching aloft, however, we expect these values to climb closer to 40 mph (30-35 knots) in the afternoon.
The image below shows the predicted wind shear values at 5 p.m. The DC region will lie along the southern edge of the higher northern wind shear values; the core of the strongest shear will be well to our north. Such strong wind shear values in an unstable atmosphere can trigger isolated supercell thunderstorms, with the best chance of damaging winds, tornadoes and large hail.
In the Washington area, torrential rain, lightning and a few pockets of strong to damaging winds or downbursts are expected. Activity will be gradual, so we don’t expect storm cells to repeatedly pass over the same area or train. But due to intense updrafts and abundant moisture at lower elevations, some places can quickly catch one to two inches of rain — enough to trigger isolated flash floods in areas that received large amounts of rain this month. this.