Storm season has arrived
The summer traditionally offers the highest chance of severe weather in southeastern Minnesota and western Wisconsin, and the past year has been a busy one for weather watchers.
"We had all kinds of severe weather," said Donna Dubberke, meteorologist at the National Weather Service forecast office in La Crosse, Wis. "We had tornados. We had flooding. We had extreme winter weather. You name it, we had it."
She noted that May, June, and July are the peak months for severe weather, with June being the prime month. Weather, however, can be unpredictable.
According to the NWS website for the Twin Cities/Chanhassen, Minnesota had 44 tornadoes in 2018 between May and September, with 25 of those happening on one day, Sept. 20.
"In 2018 there were a total of 11 tornadoes that touched Goodhue County thanks to two storms in August and another in September," said Jim Braaten, lead coordinator for the Sogn Valley SKYWARN group of the NWS.
Wisconsin averages 23 tornadoes a year.
As this year's storm season approaches, Dubberke offered some tips for people watching the weather.
"All thunderstorms have updraft and downdraft, the basic building blocks of the storm," she said. "Sun heats the ground and the warm air starts to rise."
She noted that the rising cumulus cloud looks like a "tower of cauliflower" as it builds, then flattens when it hits a layer of cool air. The cloud then condenses and begins a downdraft on the other side of the storm causing rain.
"The stronger the updraft, the stronger the storm," Dubberke said. "The downdraft is like dumping a bucket of water. It is a rush of water and air that fans out in front of the storm which can lead to straight line wind damage."
She noted that 60% of lightning occurs in the updraft of a storm cloud.
The stronger storms can develop into super cells, Dubberke explained. They produce the most hail and can evolve into tornadoes.
When the NWS issues a storm watch, Dubberke said that means there is a 50% or greater chance of a storm within the next two to six hours. She said a storm warning means the storm is imminent and will hit within a few minutes.