A recent study reveals tornado season is happening up to two weeks earlier than it did 55 years ago in Tornado Alley. The study was conducted by the Department of Land Resources and Environmental Sciences at Montana State University.

According to Live Science, Tornado Alley is located in the heart of the central and southern U.S. Great Plains and includes Nebraska, Kansas, Oklahoma and northern Texas. It is known for its destructive tornadoes. The peak of tornado season now typically occurs on May 19, as opposed to May 26 in the 1950s. In 2014, most of the United States’ 209 tornados occurred in May, and the deadliest storms were in April.

From a public safety perspective, if this trend (of an earlier tornado season) is indeed occurring, then people need to begin preparing for severe weather earlier in the year, said Greg Carbin, the warning coordination meteorologist at the Storm Prediction Center in Norman, Okla.

Earlier tornadoes may be linked to El Niño, which is associated with warm waters in the Pacific Ocean changing the air-surface pressure and atmospheric circulation. When El Niño conditions happened between January and April, high tornado activity also occurred earlier in the spring.