From the Plains to the Great Lakes to parts of the Mid-Atlantic and Northeast, the second half of May was extremely active with heavy rain and severe weather. Tornadoes occurred as far east as New Jersey, with flooding from Oklahoma to New Jersey and many places in between, along with damaging winds and hail in some locales.
Upper-level weather pattern in May; an active storm track occurred between a trough over the Southwest and ridge over the Southeast, bringing severe weather and flooding to many.
What caused this? The atmosphere basically got “stuck,” with a dip in the jet stream over the Desert Southwest and ridge over the Southeast. Energy coming off of the trough in the Southwest helped to spark heavy rain and severe weather, which then rotated around the north side of the Southeast ridge into the Ohio Valley and Mid-Atlantic. This pattern was very stagnant for the second half of May, so once the rain and storms started, they didn’t stop for any length of time.