How Severe Storms and a ‘Rain Train’ Ravaged the DC Area

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A pair of severe thunderstorms hit areas south of Washington on Wednesday afternoon; the towns of Fredericksburg and Warrenton were particularly hard hit. While the immediate DC area was spared those initial blows, it was drenched by a relentless stream of storm cells Wednesday night. This “rain train” caused areas of flooding and baffled storm watchers with its unusual north-south motion.

Storms Fredericksburg and Warrenton – with winds estimated at over 80 mph – downed hundreds of trees and led to more than 100,000 power cuts.

The Fredericksburg storm first developed north of the district before breaking into Prince William County, where it first caused wind damage. The storm then sped south along Interstate 95, knocking down trees and cables along its path – which ended south of Richmond. The winds were strong enough to strip siding from homes and even move a shed off its foundation, according to National Weather Service reports.

The Warrenton storm was relatively intense. It first caused tree damage in southern Loudoun and northern Fauquier counties around Middleburg and the Plains. It felled “dozens of trees” near Marshall, according to the weather service. In west-central Fauquier County, including Warrenton, there were “hundreds of downed trees, many in homes with at least three structural collapses,” the weather service wrote. The storm also toppled trees around Culpeper before the storm weakened.

Amid the many storms that have swept through the area, there have also been several reports of homes being struck by lightning. At least one firefighter was injured in response to lightning at a Loudoun County home.

DC area wakes up to downed trees, power outages and flooding

The storms lined up from north to south like trains along a track, dumping huge rainfall in some areas.

Some of the heaviest rains were concentrated along and just west of Interstate 81, where streams overflowed and roads were closed.

Around Washington, a storm cell train that stretched as far north as central Pennsylvania cycled through the region beginning around 7:30 p.m. and continued well past midnight. Minor flooding was reported along Rock Creek at Sherrill and Beach Drives, where several vehicles were blocked or broken down.

Typically one to two inches of rain fell in the Beltway area; throughout the region, amounts ranged from about 0.1 to over 3 inches. Here are some of the totals:

  • Wooden bridge: 3.1 inches
  • Front Royal: 2.5 inches
  • Fairfax: 2.29 inches
  • Fort Belvoir: 2.18 inches
  • Reagan National Airport: 1.86 inches
  • Rockville: 1.78 inches
  • Winchester: 1.4 inches
  • Dulles: 1.00 inches
  • BWI Marshall: 0.66 inches

Explain the storm

The Fredericksburg and Warrenton storms were isolated and occurred about an hour and 40 miles apart. The systems were compact, arc-shaped storm complexes that moved rapidly from north to south – an atypical movement for our region during the summer.

The storms started and tracked along a north-south frontal boundary and were steered by a deep northerly wind flow.

The first complex froze near Dale City around 2:15 p.m. and tracked south along I-95 before dissipating south of Richmond. The radar animation of the system is shown below. In the animation, the left panel shows radar reflectivity (rain intensity) while the right panel reveals Doppler-derived wind speed.

The storm complex begins as a solid, undulating arc of cells that then slopes rapidly and lengthens to the south. A powerful surge of downward wind was responsible for the transformation into a curved shape. These winds were picked up by Doppler radar at Sterling, Virginia, and indicated by the patch of orange colors along the leading edge of the bow.

The image below reveals the peak strength of these winds – near 88mph and in the range of 78-96mph at other times. At this distance from the radar, the lowest scanning beam was several thousand feet above the ground, so these values ​​do not reflect ground wind speeds. But they reveal the intense momentum at play in this downdraft – a large percentage of which has undoubtedly risen to the surface to create damage.

The second complex developed south of Purcellville just after 4 p.m., developing into an arcing complex as it moved rapidly south. The storm’s track picked up the strong core of the wind just west of downtown Warrenton, as can be seen in the radar loop below.

Maximum Doppler-derived wind speeds were between 90 and 95 mph, as seen in the following radar snapshot:

The high winds were the result of a straight-line flow called a downburst, which occurs when an unusually strong downdraft hits the surface and the airflow gushes outward along the ground, literally like a blast of wind. The strongest winds occur in the direction the storm is moving.

The large number of trees and the scale of the devastation appear “derecho-like”, but in fact none of these storm complexes can be called a derecho; derechos are defined by a minimum path of continuous wind damage at least 250 miles in length.

Formation of thunderstorm cells and heavy rain

Some places in the region received several inches of rain from this event, others not as much. Interestingly, the heaviest rains fell in long, parallel, narrow corridors running north to south.

This type of situation can occur when the frontal boundary that serves to lift air in thunderstorm updrafts—in this case, a nearly stationary front trending north to south—aligns parallel to the directional flow established by a deep layer of winds above the ground.

The deep-layer winds were coming from a very unusual direction for late June — due north — because the jet stream, a fast-flowing river of air in the upper atmosphere, is in a very distorted pattern. A heat dome is lodged over the southeast and the jet stream, along which the storms move, overlies it, dipping sharply over the northeast.

Brutal heat bakes the southeast, with more records expected on Thursday

A spectacular radar snapshot (above) shows one of these rain trains in action mid-evening; the corridor stretches from Harrisburg, Pennsylvania to downtown Washington.

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