Livescience.com reports that the main reason is that spring has been colder than average for much of the nation’s mid-section. Warm air over Greenland and the North Atlantic has blocked the normal flow of air from west to east and south to north.
With winds from the north, the eastern two-thirds of the United States have been socked in with Arctic air. Tornadoes are fueled by warm and muggy air.
The pattern appears to be changing with a chance of strong storms in the southern Plains states early next week.