EF1 tornado in Mercer County, New Jersey

The Windsor-Robbinsville Township tornado began on Route 130 just

south of the town of Windsor near the Assunpink Creek. A few

hardwood trees were uprooted along the highway near the Chestnut

Montessori. The building lost a portion of its roofing material

and several other hardwood trees were uprooted or snapped just

behind the property into a small wooded area. The tornado then

continued in a somewhat transient and weak manner through a series

of fields and tree lines. A few large tree branches were snapped

off near a farm home on Windsor Road and a hardwood tree in a tree

line was uprooted across the street. The sporadic tree damage

continued along Perrineville Road where a large section of a tree

was snapped off at another residence. The tornado then produced an

area of intense convergent tree damage near the intersection of

Perrineville Road and Voelbel Road where numerous trees were

snapped or uprooted. The tornado ended just downstream from this

intersection at a residence on Perrineville Road where a final

tree was uprooted. Despite its short path length, the tornado was on the ground for nearly 10 minutes, and radar data corroborates its motion as being much slower than other tornadoes on this day.

A strong shortwave trough moved east-southeastward out of the Great Lakes region on July 29. An associated, strengthening surface low also tracked out of the Great Lakes and into upstate New York. A warm front associated with this low moved through most of New Jersey and eastern Pennsylvania during the late morning and early afternoon hours. This front, combined with the remains of widespread convection to the west from the previous overnight and morning hours, brought significant cloud cover to the eastern mid-Atlantic for much of the day on the 29th. This was mainly in the form of mid and high level cloud cover, however, and temperatures still warmed to near seasonal levels behind the warm front, allowing moderate to strong instability to build. Meanwhile, the robust surface and upper level disturbances approaching the region brought both strong forcing and unseasonably strong wind shear. By mid-afternoon, an unusually favorable convective environment existed over eastern Pennsylvania and New Jersey.

The result of this environment was a rare tornado outbreak across the area. Initially, during the mid-afternoon hours, mixed convective modes over east-central Pennsylvania produced a couple instances of damaging wind and brief tornadoes as storms attempted to overcome cloud cover and some light stratiform rain in the area. With time, as storms moved into better instability and a less contaminated environment over far eastern Pennsylvania and New Jersey, they took on more supercellular structures. Multiple cyclic supercells would go on to produce several tornadoes, three of them strong (EF2+) over eastern Pennsylvania and New Jersey. Convection persisted past the sunset hour with little to no loss in intensity due to the strong forcing. The only thing that put an end to the outbreak was the coastline, as storms moved offshore towards 9 to 10PM local time. Even offshore, one supercell continued to exhibit strong rotation and likely produced a strong waterspout for tens of miles over the Atlantic.

Fortunately, and miraculously, no serious injuries or loss of life occurred as a result of this outbreak. With the passage of a cold front late on the evening of the 29th, cooler, drier, and much less active weather would grace the region for several days as clean-up efforts began.