With drier air coming into the region, the risk of severe storms reduces.

5:00 p.m. – The severe thunderstorm watch from Interstate 95 westward is lifted.

While showers and thunderstorms are dispersed throughout the region, the severe thunderstorm watch has been lifted for regions along and west of Interstate 95, as they are generally below the severe threshold.

Until about 7 p.m., an isolated severe storm is still possible east of Interstate 95.

For the most up-to-date forecast, see: PM Showers probable till sunset, then colder and drier into a lovely Thursday.

This concludes our update.

3:10 p.m. — Scattered downpours moving east of Interstate 95.

Showers with brief periods of heavy rain are spread across Maryland from Columbia to Potomac and are moving southeast. They'll cross I-95 in the next 30 to 45 minutes, but their stay will be brief.

There is little activity in Northern Virginia, however an area of downpours in southern Loudoun and northern Fauquier counties is expected to move southeast along Route 50 into our western suburbs over the next hour.

None of this activity is considered significant, but if it intensifies and becomes dangerous, we will provide an update.

2:10 p.m. – Initial storminess is advancing into Southern Maryland, while fresh storms develop to the northwest.

The violent storm that swept through Alexandria and southern Prince George's County has now made its way into northeast Charles and northern Calvert counties. It has developed into a cluster of multiple storms that will move southeast during the next hour into St. Mary's and southern Calvert counties.

To the northwest, sporadic thunderstorms have formed in northern Loudoun and Frederick counties and should be monitored as they move east-southeast toward the District's northern suburbs over the next hour or two. We'll provide updates as they approach. Continue scrolling down for a general thunderstorm forecast through the afternoon.

1:25 p.m. — Alexandria's severe storm barrels toward southern Prince George's County

A powerful storm exploded in Alexandria shortly after 1 p.m., unleashing damaging winds and hail. It is currently flying between the southwest corner of the District and Camp Springs, Maryland, at a speed of 25 miles per hour toward Andrews Air Force Base and Clinton. It is possible for damaging wind gusts of up to 60 to 70 mph and small hail to occur in addition to extremely heavy rain and lightning.

As the storm raged over Alexandria, one eyewitness described it as "ten minutes of apocalypse" on Twitter. Another stated, "I couldn't see out my window due to the amount of water, but I could hear the hail stones hitting against the glass."

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A cold front is on its way to clear the city of this hot, smokey air. However, it is possible that it will spark a few scattered severe thunderstorms along the route.

Through 8 p.m., a severe thunderstorm watch has been issued for the Washington and Baltimore metropolitan areas. The watch also extends significantly further north, through Philadelphia, New York, and Boston.

Storms are most likely to pass across Washington and Baltimore between 3 and 6 p.m., heading northwest to southeast. However, isolated showers and thunderstorms may form in the region prior to that in the early afternoon.

Along with torrential rain and lightning, storms may produce hail and brief bursts of devastating winds. Storms may concentrate east of Washington, with the greatest chance of severe weather in New Jersey and southern New York. However, a few severe storms are anticipated throughout the District, particularly in our eastern suburbs.

A severe thunderstorm watch indicates that the conditions are favorable for severe storms, but they are not guaranteed. If, on the other hand, a severe thunderstorm warning is issued for your location, it indicates that severe storms are impending and that you should seek shelter in a sturdy structure.

Discussion

Today's storms will develop along a slowly moving cold front, as depicted in the picture below, with initially scattered cells clumping together into larger aggregates and line segments as the afternoon progresses.

Storms will approach from an uncommon direction, northwest. They are being fueled by an unstable, humid air mass that is being pushed westward by westerly-southwesterly winds. A trough or dip in the jet stream is approaching in the upper atmosphere, boosting the dynamic uplift over the Mid-Atlantic.

Mid-level winds are strengthening within the trough, resulting in wind shear (shown below). Wind shear acts to separate the updraft from the downdraft in storm cells, hence boosting storm strength.

Wind shear speeds of 35 to 40 mph will combine with the air's high buoyancy (instability) to form longer-lived clusters of storm cells, dubbed multicell thunderstorms. Notable is the dearth of cell coverage depicted in the high-resolution simulations (see below). This could be because the low-level airflow is descending mountains to our west, suppressing storm formation and slightly drying out the lower atmosphere.

Severe storms that coalesce along the Interstate 95 corridor have the potential to produce torrential downpours, strong cloud-to-ground lightning, hail up to a quarter in size, and peak wind gusts of 60 to 70 mph.