It started with a powerful line of severe thunderstorms that produced widespread damaging straight-line winds and multiple embedded weak tornadoes across the state of Wisconsin.

[2] As a frontal-wave low and associated warm front moved across the Great Lakes region, an extremely unstable and increasingly moist environment was in place across part of Minnesota and most of Wisconsin.

By the late afternoon and early evening hours, significant moisture advection and daytime heating had occurred, with steep lapse rates present and CAPE values reaching up to 4500 J/kg across the threat area.

However, with helicity values at up to 600 J/kg, and effective shear reaching 70 kts, a secondary threat for tornadic supercells and embedded circulations within the line was also present, and a 10% risk area for tornadoes was outlined.

The storms produced additional wind damage in the extreme northern portions of Illinois and Indiana, before weakening to sub-severe levels and pushing though the Ohio Valley region by sunrise.

However, areas of enhanced helicity from remnant outflow boundaries were present as well, and the low-level wind profile became favorable for rotating supercells and tornadoes as the day progressed.

By the evening, the storms moved towards the coast and out into the Atlantic Ocean, including a supercell that spawned an EF2 tornado which struck High Bar Harbor, New Jersey, resulting in structural damage and minor injuries.