Severe thunderstorms ripped through parts of mid-Atlantic on Wednesday, June 3, 2020, leaving at least three people dead and more than half a million people without power. On Thursday morning, June 4, the National Weather Service (NWS) confirmed the event was a 'derecho' - a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system.
Areas in the northern Plains, Upper Midwest, and eastern Great Lakes were placed on a severe weather alert on Tuesday night, June 2.
In central Minnesota, a line of storms pushed an outflow boundary south into an unstable air mass over the southern region. Severe storms spawned hail, strong winds, and tornado reports. In Waldorf, winds gusted to 101 km/h (63 mph), with hail pummeling the area.
Ride along with the derecho trekking across PA & NJ.— Dakota Smith (@weatherdak) June 3, 2020
A terrific visual via GOES-East. pic.twitter.com/6LZXnEP60t
From Charmain Jains in Waldorf, MN: was/is some serious hail tonight pic.twitter.com/yMmMogZ9V7— Sven Sundgaard (@svensundgaard) June 2, 2020
The threat moved east to mid-Atlantic on Wednesday, June 3. According to the NWS, more than 185 damaging wind reports were received, while more than 525 000 customers were left without electricity in Pennsylvania and New Jersey at the height of the storm.
Three fatalities were reported in Montgomery County, Pennsylvania, in separate incidents involving downed trees. Two people lost their lives in Lower Merion when trees collapsed on their cars, while a third victim died when a tree fell on him in Lower Moreland.
As of Thursday morning, June 4, more than 350 000 customers were still without power.
"The storms raced across Pennsylvania and New Jersey, moving eastward at over 129 km/h (80 mph) at times," said Accuweather meteorologist Brian Thompson.
South Philly pic.twitter.com/pJBttVb5vi— Lauren (@istillcode) June 4, 2020
Aerial view of the intense line of storms moving through central Bucks County PA pic.twitter.com/cdXX922KUo— Ray Leichner (@stormchaserray) June 3, 2020
"We are getting widespread reports of damage across southeast Pennsylvania from these thunderstorms. This is a real situation and we urge people to take cover to protect themselves now," the NWS Mount Holly posted in a tweet, after issuing a tornado warning that covered Philadelphia, Pennsylvania, and Camden, New Jersey, on Wednesday night.
Tropical-storm-force winds destroyed roofs and blocked roads. In Reading, Pennsylvania, a thunderstorm produced a wind gust to 134 km/h (83 mph), which might have been the fastest wind speed on record at an official site in Berks.
AccuWeather meteorologist Alan Reppert quoted retired meteorologist Jeffrey R Stoudt, who believes that the gust beat a 132 km/h (92 mph) wind record set in 1954 during the passage of Hurricane Hazel's remnants.
Another gust of 109 km/h (68 mph) was recorded at Northeast Philadelphia Airport and 117 km/h (73 mph) in the Homlesburg area.
"It appears the area of damaging wind gusts extended for about 155 km (250 miles) from northwestern Pennsylvania to the New Jersey coast on Wednesday," AccuWeather's Chaffin Mitchel noted.
"Fast-moving lines of storms have an easier time producing widespread damaging winds, which this line did over southeastern Pennsylvania and portions of New Jersey," said Thompson.
On Thursday morning, the NWS Mount Holly confirmed that the intense line of severe thunderstorms was a derecho -- widespread straight-line wind storm sometimes referred to as inland hurricane.
Featured image credit: NOAA/GOES-16. Acquired: 14:10 UTC on June 3, 2020