How can a tornado occur in January?
Tornadoes can happen whenever atmospheric conditions are suitable, says Steve Ackerman, professor of atmospheric science at UW-Madison. Over the years, Wisconsin has had at least one tornado in every month except February.
“To get any severe weather, we need really warm, moist air near the ground, and cool air aloft, which is typical of the spring, but not winter. But on Jan. 7, the temperature was in the 60s, and the snow was evaporating, moistening the lower level of the atmosphere, so we had spring-like conditions in Southern Wisconsin,” including Kenosha County.
The two tornadoes that struck Wheatland were powerful enough to destroy an estimated 26 houses, and damage about 75 others. No deaths or serious injuries were reported.
Tornadoes were also reported or suspected on the same day in Missouri, Arkansas, Illinois and Oklahoma, due to the cool air overtaking a warm, moist surface layer.
Another contributing factor on Jan. 7 was wind shear – a difference in wind directions between the lower and higher atmosphere. “The wind at the ground was from the south, and in the upper atmosphere it was from the southwest, which allowed the storms to develop rotation,” Ackerman says.
Once the warm, moist air starts to rise and spiral, he adds, the jet stream “acts like a vacuum, and as the air moves upward, the storm explodes.”