You're not imagining it: There have been a lot of tornadoes this spring. Here's why.

If you think there have been a lot of tornadoes this year, you're right: With at least 850 confirmed tornadoes so far and several major tornado outbreaks, it ranks among the busiest years in recorded history.

It's at least the sixth-busiest in the past 30 years, based on preliminary information from the Storm Prediction Center. That number is likely to rise as the National Weather Service continues surveying and confirming damages from the April and May tornado reports, which were up significantly over previous years. Even some of the most veteran storm chasers have been astounded by tornado activity so far this year.

"We've had a lot of tornadoes and several 'big' days," said Harold Brooks, a senior scientist at the National Severe Storms Laboratory in Norman, Oklahoma.

Preliminarily, the U.S. has seen four days with at least 30 tornadoes rated EF1 or stronger, Brooks said. The average is two a year. That likely puts 2024 in the top 10% of years.

Dozens dead from spring 2024 tornadoes

Since April 26, the U.S. has experienced 18 killer tornadoes in which 36 people have died. Half the victims were in mobile homes.

• May 27: At least 22 people killed in Arkansas, Kentucky, Oklahoma and Texas.

• May 6-8: Multiple tornadoes hit northeastern and central Oklahoma, including one in Barnsdall, Oklahoma, that killed one person and destroyed 30 to 40 homes. They were among dozens of tornadoes in the U.S.

• April 27-28: Tornadoes struck 12 Oklahoma counties, leaving at least four dead and 100 injured.

Sheriff Ray Sappington of Cooke County, Texas, a veteran of more than 30 years in law enforcement, was overcome with emotion as he talked to the news media overnight Saturday night after a deadly tornado.

“I’m still emotional,” Sappington told USA TODAY on Tuesday. The EF3 tornado traveled 48 miles across three counties, one of four tornadoes in the Dallas/Fort Worth weather service region. Its winds of up to 140 mph killed seven and injured 100, the weather service said.

Sappington has responded to countless storm scenes, but said it's "different when you’re the sheriff and it’s in your county.”

“I told the parents of a 2-year-old and a 5-year-old that their kids were dead and I led them in there to make the identification and watched that,” he said. “It’s just tough.”

Why has this tornado season been so active?

So far, the weather service puts the number of tornadoes at 857 though May 27, based on preliminary reports.

Meteorologists interviewed by USA TODAY blame an active jet stream, coupled with a series of powerhouse storms rolling from the West Coast across the nation's midsection. It has "been a great recipe for numerous severe thunderstorms and tornadoes" over the past few weeks, said meteorologist Peter Mullinax of the Weather Prediction Center.

The storms have been able to tap into a very warm, moist atmosphere that's been sitting over the Gulf of Mexico, AccuWeather meteorologist Paul Pastelok added.

Both meteorologists said the active jet stream is being powered in part by the diminishing El Ni?o, a climate pattern in the Pacific Ocean that affects weather in the U.S. and around the world.

The storm activity has come in waves this year, with unusual warmth earlier in the year fueling more storms, said Victor Gensini, an associate professor of meteorology and severe weather at Northern Illinois University.

The big heat dome over Central America and the Gulf of Mexico "allows for this reservoir of gasoline, in this case moisture, to store up," said Gensini, in the field on Tuesday in Texas, where additional severe weather is expected over the next week over the high plains of West Texas and eastern New Mexico.

Typically this time of year, a cold front will pass over the region and shut down storm activity but it's difficult for cold fronts to push down into the heat dome, he said. "The moisture remains in place, that's one of the fundamental ingredients you need for tornadoes."

Looking ahead, Pastelok said the stormy pattern should continue into June, but that the month shouldn't be as busy as May was.

Is climate change causing more tornadoes?

Additional research is needed to understand the role climate change is playing in tornado activity, Gensini said. "I think it's safe to say climate change plays a role, but is it 10%, 5% or 1%, I don't think we know that right now without a bigger push to understand the role of climate change in these events."

For example, climate scientists say they’re not confident in a long-term trend in larger numbers or intensity of tornadoes. Instead, what appears to be happening is that tornadoes are occurring at different times and in different places than they have in the past, making old certainties less useful in predicting when and where communities are at risk.

Tornado warning: Twisters are hitting more frequently and dealing more deaths in the South

Among the oddities observed this year:

• April was well above average for the number of tornadoes, Brooks said.

• Some areas have been hit repeatedly, or by multiple tornadoes. Gilmer County, Georgia, experienced four tornadoes on May 8 and 9.

• The Dallas/Fort Worth weather service office reported four tornadoes in its region over the weekend, then gusts of up to 77 mph in Dallas and Arlington on Tuesday.

• Illinois experienced several strong storms in February, a time of year in which they are certainly known to happen, but the spacing was surprising, Gensini said.

“We had tornadoes in similar areas just a few weeks ago,” Gensini said of the Illinois tornadoes. Couple the earlier than typical tornadoes with some record-breaking temperatures and folks begin asking why that's occurring. “To me, this is a good example of the new norms associated with climate change.”

Cities mostly spared – so far

As devastating as this season has been, the worst storms have not hit densely populated areas.

"We've had some terrible disasters and loss of life, but thankfully some of the most violent storms so far this year have missed highly populated areas," Gensini said.

What to do during a tornado warning: Staying safe at home, outside, in a car

Gensini hopes the trend will continue but worries about an outbreak hitting a heavily populated area.

"From a perspective of somebody who's continually watching these events, it's a matter of time before we see 'the big one.'"

This article originally appeared on USA TODAY: Is 2024 a record year for tornadoes? Data shows a busy, deadly spring.