Tornadoes can strike certain parts of the U.S. at any time of year, but April, May and June are overwhelmingly the most active when it comes to thunderstorms spawning these destructive forces of nature.
Here’s a look at several reasons why these springtime months are such a dangerous time of year for tornadoes.
Spring’s tornado threat area shifts and grows in size: The areas with the biggest threat of tornadic thunderstorms slowly change as we press through the springtime months.
Much like March, parts of the Deep South still have a heightened threat of tornadoes in April. The greater potential for tornadoes then moves toward the Plains and Midwest from May to June. You can see this general month-by-month progression in the maps below.
The peak in spring’s tornado activity is illustrated by recent weather history: The U.S. averaged 1,250 tornadoes annually from 2003 to 2022. About 54% of those tornadoes occurred in April, May and June.
The most tornadoes typically happen in May, with an average of 278. This is followed by April and June, which average 203 and 188 tornadoes per year, respectively.
Of course, these are averages. How tornadic these months are in a given year can vary, often dependent on when major tornado outbreaks occur. Some recent Aprils demonstrate this, with 147 tornadoes striking the U.S. last year, 219 in 2022 and just 78 in 2021.
Tornado intensity is also a factor in making this a dangerous time of year: About 58% of all twisters rated F3/EF3 or stronger (1950-2012) struck in those three months, according to statistics compiled by Dr. Greg Forbes, former severe weather expert at The Weather Channel. This rises to 69% when examining tornadoes F4/EF4 or stronger.
The most violent F5/EF5 rating has been assigned to 59 tornadoes dating back to 1950, and all but 10 of those occurred in April, May or June.
All tornadoes pose a threat, but intense twisters account for a higher number of fatalities and damage. About 83% of the deaths from 2019 through 2023 were from tornadoes rated EF3 or stronger, according to data from NOAA’s Storm Prediction Center.
The ingredients that come together to spawn tornadoes align most often in spring: Outbreaks of tornadoes occur when a storm system propelled by a strong, southward dip in the jet stream punches into the Plains, Midwest or South. The jet stream provides deep wind shear, or changing wind speed and direction with height, that can help form tornadic thunderstorms when moisture from the Gulf of Mexico is sufficient.
In spring, the jet stream begins to make its annual northward retreat toward the Canadian border.
That’s why the potential for tornadoes in the South is much lower in June compared to April. Although moisture is abundant across the South in late spring, the strong jet stream needed to help make conditions favorable for tornadic thunderstorms is usually absent.
Farther north, it’s the opposite effect, because the overlap between the jet stream and increasing moisture in the atmosphere happens more often there later in spring.
Now is a good time to review your plan for severe weather this spring and any other times of the year tornadoes might threaten your area.