The Fredericksburg and Warrenton storms – with estimated winds of over 80 mph – knocked down hundreds of trees and led to more than 100,000 power outages.
The Fredericksburg storm first developed north of the district before erupting in Prince William County, where it first caused wind damage. The storm then raged south along Interstate 95, taking trees and wires down the entire trail – which ended south of Richmond. The wind was intense enough to remove siding from the homes and even move a shed away from its foundation, according to reports from the National Weather Service.
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 western and central Fauquier County, including Warrenton, there were “hundreds of trees blown down, many into homes with at least three structural collapses,” the Weather Service wrote. The storm also knocked down trees around Culpeper before the storm weakened.
Amid the numerous storms sweeping through the region, there were also several reports of homes hit by lightning. At least one firefighter was injured when he responded to lightning in a home in Loudoun County.
The storms piled up in the north to southern rows which took along a track, unloading huge amounts of precipitation in some areas.
Some of the heaviest rain focused along and just west of Interstate 81, where streams overflowed and roads were closed.
Around Washington, a train of storm cells, stretching as far north as central Pennsylvania, cycled through the area from about 7:30 p.m., continuing well after midnight. Minor floods were reported along Rock Creek at Sherrill and Beach operated where several vehicles were stranded or disabled.
In general, one to two inches of rain fell in the Beltway region; over the wider range, the amounts ranged from about 0.1 to over 3 inches. Here are some of the totals:
- Woodbridge: 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
Explains the storm
The Fredericksburg and Warrenton storms were isolated and took place about an hour and 40 miles apart. The systems were compact, arc-shaped thunderstorm complexes that traveled rapidly from north to south – an atypical movement for our region in summer.
The storms started and tracked along a north-south oriented frontal boundary and were controlled by a deep wind current from the north.
The first complex solidified near Dale City around noon. 14.15 and tracked south along I-95 before disappearing south of Richmond. The system’s radar animation is shown below. In the animation, the left panel shows radar reflectivity (intensity of rain), while the right panel reveals Doppler-derived wind speeds.
The storm complex starts as an undulating, solid arc of cells, which then rapidly bend out and extend to the south. A strong wave of downward wind was responsible for the transformation into a pliable form. These winds were detected by the Doppler radar in Sterling, Va., And displayed by a spot of orange along the leading edge of the bow.
The image below reveals the peak strength of these winds – almost 88 mph, and in the range of 78 to 96 mph 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 wind speeds at the ground. But they do reveal the intense momentum that is at stake in this downdraft – a large percentage of which no doubt came to the surface to inflict damage.
The second complex developed south of Purcellville just after noon. 16, and expanded into an arc complex as it traced rapidly south. The trail of the storm took the violent core of wind just west of Warrenton’s center, as can be seen in the radar loop below.
The maximum Doppler-derived wind speeds were in the range of 90 to 95 mph as shown in the following radar snapshot:
The violent winds were the result of a linear flow called a crash, which occurs when an unusually strong downpour hits the surface and the airflow rises outward along the ground, literally like a gust of wind. The strongest winds occur in the direction the storm is moving.
The large number of trees and the extent of the destruction seem “derecho-like”, but in fact none of these storm complexes are qualified as a derecho; derechos is defined by a minimum course of continuous wind damage of at least 250 miles long.
Training of storm cells and heavy rain
Some places in the region received several inches of rain from this event, others not near as much. Interestingly, the heaviest rain fell in long, parallel, narrow corridors oriented from north to south.
This type of situation can occur when the frontal boundary that serves to lift the air into thunderstorm upwells – in this case an almost stationary front oriented north to south – is flush in parallel with the control current established by deep wind layers above the ground.
The deep gusts came from a very unusual direction in late June – heading north – because the jet stream, a river of fast-flowing air in the upper atmosphere, is in a highly distorted pattern. A heating dome is placed over the southeastern part, and the jet stream, along which storms trace, rides over it and takes a sharp dive over the northeast.
A dramatic radar snapshot (above) shows one of these rain trains in action in the middle of the evening; the corridor stretches from Harrisburg, Pa., to downtown Washington.