Chainkeen|US tornado activity ramps up: Hundreds of twisters reported in April, May

Dozens of tornadoes left devastation in their wake this week,Chainkeen ripping through communities and leaving crumpled mobile homes, damaged roofs and a trail of broken and shredded trees from Oklahoma to Michigan. 

The destruction suggests May is starting like April ended, with an unusually large number of twisters. 

"We at Michigan Storm Chasers were just talking about how crazy the last month has been and then boom, yesterday happens,” Alex Melendez said Wednesday morning, hours after at least four tornadoes slammed the state.

“We also hope that May doesn’t continue to be so violent,” said Melendez.  

Across the nation in April, 381 tornadoes were reported, according to preliminary storm reports from the National Oceanic and Atmospheric Administration's Storm Prediction Center, which are likely to be adjusted slightly downward after review.

That's roughly twice the long-term average number of tornadoes for the month.

It's also the third most tornadoes ever counted in April, dating back to 1950,  said Harold Brooks, a senior scientist at NOAA's National Severe Storms Laboratory.

Only April 2011 and April 1974 had more tornado activity.

What to do during a tornado warning:How to reduce your risk of injury at home, outside, in a car

Iowa led the nation in April tornadoes

Among the states with the highest reported tornado activity in April, Iowa stands out with 56 tornado reports. That number is "a bit on the high side,” said Craig Cogil, a meteorologist with the National Weather Service office in Des Moines who tracks the state’s tornado numbers. As the storm reports are verified in the weeks ahead, Cogil said that number will drop down to the low 40s.

Even if the final number ends up near 40, Cogil said it would still be a record. The previous high for April was 40, set in 2001. The state’s average for the entire year is around 50, he said. 

One death was reported in April, during an outbreak on the 26th, Cogil said. 

Other states that saw dozens of tornadoes in April were Nebraska (47), Kansas (38), Oklahoma (38) and Missouri (33). Kentucky and Texas each had 22.

What states have seen the most tornadoes in May?

At just one week into May, the storm center's data shows 32 preliminary tornado reports in Texas, where the monthly average for May is 38, and 10 in Michigan, where the monthly average for May is 3.

The Michigan tornadoes on Tuesday demolished mobile homes in a neighborhood near Portage, Michigan, and heavily damaged a FedEx distribution facility.

Why the increase in tornado activity? 

All the right ingredients have been in place, Brooks said. An active pattern – with atmospheric waves moving through at 30,000 feet above the ground – was “bringing everything together.”

Brooks and Cogil point out the patterns are different every year. 

“Some years it’s more active to the south or to the north,” Cogil said. This year, Iowa has been in “a very active pattern.” 

“The jet stream is in close proximity and we've seen a lot more storms,” Cogil said. “We’ve got a good stream of moisture coming up from the Gulf of Mexico and interacting with the jet stream and producing these tornadoes we’ve seen.”

The national average for May is 275 tornadoes, and the storm center has amassed roughly 90 reports so far.

It remains to be seen how the rest of May plays out, Brooks said, because it’s difficult to predict long range activity in the spring.

Dinah Voyles Pulver covers climate and the environment for USA TODAY. Reach her at dpulver@gannett.com or @dinahvp.