2021 Super Outbreak

The 2021 Super Outbreak was the most violent tornado outbreak in history along with the costliest outbreak and had the most tornadoes ever recorded in a 24 hour period. 300 tornadoes touched down in just 24 hours, with 102 violent tornadoes (EF4+). These tornadoes caused 13 billion in damages, and killed 330 people.

Meteorological synopsis
A deep upper level cyclone developed over Saskatchewan during the afternoon of May 10. The low swung into the Dakotas and Minnesota by midnight, delivering and unseasonably warm airmass, which settled across much of the area. The low was tied to a cold front, which lingered behind the system, prompting storm development.

First system
A squall line emerged just south of the canadian border at 11:45 AM, about 30 miles north of Grand Forks. The storm swung through Minnesota, spawning an outflow boundary across Iowa and Illinois. Supercells were arising as the storm migrated across lake superior.