Billion-dollar disaster numbers have increased since 1980. The annual average is 6.3 events, but the annual average for the last 5 years is at 12.6 disasters.

Dr. Harold Brooks with the National Severe Storms Laboratory has noticed an increase in the number of tornado outbreaks in the United States. He shared this information through a Climate Central webinar this summer.

Since 1970 the average number of outbreaks has increased from one to four a year. For the study, a tornado outbreak is categorized as one day with at least 25 or more EF-1 or greater tornadoes.

“So that is a really large change that’s taken place. We haven’t had fewer than 2 days in the last 15 years and in fact this year we’ve already gone passed that,” Brooks said.

Preliminary numbers from the Storm Prediction Center show that across the United States, there have been 17 days with at least 25 tornadoes over a 24 hour period.

Right now Memorial Day tops the list with 78 tornadoes.

“The number of big days has increased. As I said, we don’t fully understand that processes yet, and there’s a lot of work being done to try to look at that, but it’s a fairly hard question because the physical link between tornadoes and large scale climate aren’t fully understood yet,” Brooks said.

The trend shows both tornado outbreaks and yearly global temperatures are increasing.

Since 2003 there have been at least two tornado outbreaks each year.

Ohio is listed in 20 tornado events that cost the U.S. at least a billion dollars. This does not mean Ohio saw the most damage. Each decade the number of billion-dollar tornado events impacting Ohio has increased. In the 1980s there was one major event. In the latest decade, 10 major tornado events impacted the state.

Brooks noted in the study, there is no clear trend that there is an increase in tornado intensity.

“What has changed is the number of days per year with Tornadoes and the number of days per year with a lot of Tornadoes,” Brooks said.

The blue line indicates days in the year with tornadoes. The number of days with at least one tornado is going, but the number of tornadoes in one day is going up.

Memorial Day is included in a four-day tornado outbreak that impacted 12 states from the Rocky Mountains to the Atlantic Ocean. The entire outbreak is estimated to cost 3.2 billion dollars.

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According to the National Centers for Environmental Information, Memorial Day is one of 10 major weather disasters in the U.S. this year.

The NCEI also organizes billion-dollar disasters by state. Ohio was impacted by four events this year, an Ohio Valley severe weather event Feb. 23-25, the April 13 Tornado Outbreak across the Southeast, the Memorial Day Tornado Outbreak, and historic flooding across the Plains, Midwest, and South from March 15 – July 31.

In the last five years, there have been 10 or more billion-dollar weather disasters each year.