On the morning and early afternoon of June 3, 2020, a powerful derecho (a line of windstorms moving together) crossed Pennsylvania and New Jersey, causing four confirmed fatalities. It was the deadliest derecho in the region since 1950.
The storms were part of a mesoscale convective system (a complex of associated thunderstorms) which formed just outside of Oil City, Pennsylvania, and began moving eastward across Lake Erie just after 5 a.m. (EDT). The Storm Prediction Center (SPC) made its first warning around 8:30 a.m., and damaging wind reports began about 20 minutes later. A severe thunderstorm watch was put into effect around the region just after 10 a.m., as warm, humid temperatures further destabilized the squall line. By the time that the storm crossed the Delaware River into New Jersey, wind speeds were equivalent to those of a Category 1 hurricane. By 2 p.m., the storm had dissipated off the coast.
Fallen trees and power lines resulted in four deaths across southeastern Pennsylvania. Wind speeds also resulted in severe property damage from fallen trees, and at least two buildings lost their roofs. Over 850,000 individuals lost electricity due to storm damage, and for many, power was not restored for several days. PECO Energy recruited service crews from outside the region to work on restoring electricity in homes, while drone technology was used to survey the damage. Repairs were slowed by several days of severe weather following the initial storm, but by June 6, the thunderstorms had come to an end.
Meteorological history
A mesoscale convective system that formed just outside of Oil City, Pennsylvania, began moving eastward across Lake Erie around 5:12 a.m. EDT on the morning of June 3, 2020. By 8:32 a.m. EDT, the storm system had moved into northwestern Pennsylvania, and the Storm Prediction Center (SPC) warned that as it progressed and encountered the warmer temperatures in the eastern part of the state, there was a greater threat of severe weather. The first reports of damaging winds emerged twenty minutes later. The SPC issued its first severe thunderstorm watch at 10:05 a.m. EDT, covering an area that stretched from west-northwest of State College, Pennsylvania, and southeast of Lakehurst, New Jersey, as well as north and south. By 10:34 a.m. EDT, the squall line was moving into southeastern Pennsylvania, where the warm, humid temperatures would further destabilize the system.
While there were few damaging wind gusts of or more while the storm moved across western and central Pennsylvania in the morning, the storm intensified by noon. Significant wind damage began as the system entered Berks County, Pennsylvania, and continued through the Delaware Valley towards Ocean County, New Jersey. The wind gust measured in Berks was the strongest on record, surpassing the gusts recorded during Hurricane Hazel. Social media footage from the storm showed funnel clouds in Philadelphia and hail in State College, Pennsylvania. The storm crossed the Delaware River around 12:30 p.m. EDT and reached Long Beach Island by 1:15 p.m. The derecho was most severe in Ocean County, New Jersey, where wind speeds were measured at in Beach Haven and in Surf City. By 2 p.m. EDT, the storm had moved off of the New Jersey coast.
Wind speeds reached in New Jersey were equivalent to a Category 1 hurricane, but no hurricane, tropical storm, or tornado was recorded. To be considered a derecho, the National Weather Service states that wind damage must extend at least and include gusts of at least . An early report from climatologist David Robinson inferred that the storm had traveled in hours, which would have given it an average speed of . Derecho storms are also known for the characteristic bow-like shape of their radar profile The SPC confirmed on the afternoon of June 3 that the storm was classified as a derecho. Meteorologist Lee Robertson believed that the storm was rare even among other derecho events both for its "duration and intensity", particularly the wind speeds of . The evening before, a "ring of fire" pattern had settled over most of the contiguous United States. In such a scenario, thunderstorms moving across the ridge of a high-pressure area feed off of both the warm, humid air of the high-pressure region and the adjacent jet stream winds, causing rapidly-intensifying, unpredictable storms. In the days preceding the derecho, that weather pattern had caused damaging thunderstorms in the Midwestern United States.
