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The region was located between an exceptionally warm air mass over the Southeastern States and an unseasonably cool air mass located over the Northern Plains States.  At the surface, this was delineated by a weak quasi-stationary boundary that roughly extended from the lee of the Rockies into the Southern Plains across the Mid-Mississippi Valley into the Northeastern states.  Being on the western edge of the surface high pressure, the region was continually being fed by the warm and moist air mass from the Gulf of Mexico.

The upper level pattern was dominated by a ridge over the Southeastern States and eastern Gulf of Mexico while a longwave trough was centered along the West Coast.  Every 2-3 days, a storm system would be ejected from the West Coast trough only to replaced by another storm system digging southward from Alaska. As these systems ejected from the trough, they would cause a surface low to form in the lee of the Rockies that would then move up the front towards the Great Lakes into the Northeastern States.  This produced several rounds of severe weather as well as heavy rainfall.


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    All Tornado Tracks from 20-22 May 2019
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