This week, Wisconsin was drenched by heavy rainstorms. Some parts of Milwaukee saw as much as six inches of rain, according to the MMSD. It's caused flooding in some streets and homes.
We’re not used to so many days of extreme weather this time of year. But Wisconsin’s state climatologist, Steve Vavrus, says the month we’re in doesn’t matter that much.
Vavrus directs the Wisconsin State Climatology Office.
“We need to consider what the conditions actually are outside on a given day. It doesn’t matter if the calendar said early April, we need to be prepared and take seriously any watches that are issued by the National Weather Service,” Vavrus says.
He says April has been unusual in several ways.
“Wisconsin doesn't usually get such severe weather this early in the season. Our severe weather season is usually May through August,” Vavrus says.
He adds that storms have impacted “such a wide area of the state. It's not just been localized thunderstorms. These have been very widespread types of outbreaks.”
Vavrus says warm, humid air has fueled the severe thunderstorms.
"We've also had the right dynamical forcing, meaning that we have weather fronts. We've had stationary fronts and warm fronts hanging around the region, and those fronts give the air enough lift. And so when you have lift from a front and you have enough warm humid air for fuel, you have the ingredients for some thunderstorms, which if they become strong enough, can even become severe and produce hail," Vavrus says.
Historically, May through July have been Wisconsin’s biggest months for hail.
"Our three biggest months for hail in our state are May, June, July — yet, we've had those conditions just right this week, particularly Tuesday around southcentral Wisconsin in particular,” Vavrus says.
Tornadoes have been reported including in Juneau County. “So that's to be taken very seriously as well. So the combination of high wind and hail and then the heavy rains, all three conspired to make a very difficult week in Wisconsin,” Vavrus says.
He says we've already surpassed record April rainfalls.
“Green Bay had its wettest April by far, and we're only halfway through the month," Vavrus says. "And as of [the morning of April 16,] I think Milwaukee is now experiencing its wettest April on record. And no doubt that these numbers, these ranks will climb as we go further into the month,” Vavrus says.
He says climate change is one of the forces driving these storms, providing the ingredients for extreme weather events.
"We are seeing an extension of our severe weather season from the middle of summer toward the shoulder months and seasons of spring and fall," says Vavrus. "When we have warm, humid, unstable atmospheric conditions, as we've had much of this week, conditions are favorable for developing thunderstorms, some of which can become severe."
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