SIOUX FALLS, S.D. (KELO) – The month of May is ripe for severe weather in South Dakota, northwestern Iowa and southwestern Minnesota. 

One year ago, severe weather struck early in May with the May 12, 2022 derecho. That storm event produced more than 150 damaging wind reports, 59 significant wind gusts (75 mph or higher) and resulted in two deaths in South Dakota. The National Centers for Environmental Information listed the May 12, 2022 derecho as a billion-dollar disaster event. 

When it comes to predicting severe weather, longtime KELOLAND meteorologist Brian Karstens said a number of factors have to come together. The month of May, when the weather season is changing from spring to summer, can have those factors as warmer temperatures become more and more regular. 

“If you recall, that day (May 12, 2022) was 94 (degrees),” Karstens said. “You had a pretty potent concoction of weather ingredients – you had a lot of steep humidity that came up out of the gulf (Gulf of Mexico) combined with excessive heat.” 

Photos from May 12, 2022, storm and aftermath

Karstens said the biggest difference so far from May 2023 to May 2022 is cooler average temperatures but that is starting to change already in the first full week of May. 

“We anticipate over the next seven days, we’re going to start to warm up. We’re going to pick up some 70 degree weather,” Karstens said. “As we start to warm the atmosphere, we also are going to start to see more humidity coming in later in the week.” 

Karstens said the month of May is a good time to have plans in place to react to severe weather. 

“We are now starting to ramp up into what is traditionally the more active severe weather season,” Karstens said. “This month can change wildly. Last year, we all found out how quickly these things can change.”

Like many severe weather storms, Karstens said meteorologists and weather officials had a good forecast for severe thunderstorms and tornadoes. The National Weather Service Storm Prediction Center issued a “particularly dangerous situation” severe weather watch. 

“When the weather turns bad, are you informed? Are you getting that stream of information?” Karstens said. “That’s what we’re here for. And, of course, we have a lot of resources at” 

May tornadoes in South Dakota 

Some of South Dakota’s worst tornadoes have occurred in the month of May. 

In the past 30 years, there have been 17 tornadoes listed as F3 or stronger in South Dakota and eight of them have occurred in the month of May. One of South Dakota’s deadliest tornadoes – the Spencer tornado in 1998 happened on May 30. 

For tornadoes listed at F2 or stronger, there have been 82 tornadoes in South Dakota and more than half of them occurred in May. 

The Castlewood gym after the May 12, 2022 tornado.

Last year, there were five tornado reports in May, including the May 12 tornado in Castlewood and a May 30 tornado in Deuel County. 

Eight years ago, a May 10, 2015 tornado in and near Delmont injured nine people. 

In the past 10 years, tornadoes have also occurred in the months of June, July, August, and September.

Summer 2023 weather pattern 

KELOLAND meteorologist Scot Mundt is predicting a wetter and warmer-than-average summer in KELOLAND. For the months of May through August, Mundt is predicting above-average rain and temperatures. 

The first week of May provides an example of that wetter and warmer pattern. 

Karstens said the 10-day rainfall forecast is looking wetter across much of the plains and more 70-degree days are in the forecast. 

What is a severe storm? What is a significant severe storm? 

The Storm Prediction Center says severe storms contain wind gusts of 58 mph, hail at least one inch in diameter and the possibility of a tornado.

A significant severe storm will have wind gusts of at least 75 mph, hail at least two inches in diameter and a tornado of at least EF-2 rating.