A history of Iowa’s Tornadoes

A creation of Iowa’s Climatology by Meteorologist Nick Stewart

TORNADO DATE AND TIME

Using the Storm Prediction Center database as well as summaries from the National Weather Service, 2,650 tornadoes have occurred in the state of Iowa from 1953 through 2018.

Tornadoes have been reported in every month of the calendar year.

June is the most active month of the year with 28.8 percent of all tornado reports (763) closely followed by May with 24.3 percent (643). In total more than half of Iowa’s tornadoes occur during the months of May and June.

January is a fairly unique year in Iowa regarding tornadoes as it stands at number 10 in total number, however all fifteen tornadoes occurred on the same day: January 24, 1967.

Tornadoes have struck Iowa in every hour of the day but there is an undeniable peak in the late afternoon and early evening. The data used for this summary is strictly utilizing start time for simplicity.

Between 4 p.m. and 7 p.m., 1024 tornadoes hit Iowa accounting for 38 percent of all tornadoes. In fact 91.8 percent of all Iowa tornadoes occurred after noon. Just nine tornadoes were reported between 7-9 a.m. on seven different days.

The mean start time for tornadoes is 4:30 p.m.

TORNADO DEFICITS

Since 1953 Iowa has not gone a full year (365 consecutive days) without a tornado. The longest streak on record is 360 days between reported tornadoes. On May 24, 2012 at 4:56 p.m. CDT an EF-1 tornado struck Fayette County. The next tornado wasn’t until May 19, 2013 when an EF-0 tracked for a little over two miles in Dallas County.

Only one other streak without a reported tornado hit the 300-day mark and that was between 1955 and 1956.

There have been 41 instances of 200+ days without a tornado.

FIRST TORNADO AND YEARLY COUNTS

Every year since 1953 has had at least one tornado. The years 1956 and 1957 were the only years with tornado counts in the single digits, both with seven total.

The earliest first tornado in a calendar year was on January 24 in 1967.

On average, the first tornado is confirmed on April 10.

The latest a tornado was reported in Iowa was June 7 in 1978. The other latest tornadoes on record were June 1, 2010; May 29, 1980; May 26, 1972; and May 19, 2013.

Between 1953 and 2018 an average of 40 tornadoes hit the state of Iowa. The 10-year running average is 46 tornadoes in a year, the 15-year running average is 54 tornadoes in a year and the 30-year average is 51 tornadoes in a year.

The extremes are quite literally extreme. Both 1956 and 1957 had just seven tornadoes. On the other end of the spectrum 2004 tallied 122 tornadoes. Only two other years were in the triple digits - 2001 with 107 and 2008 with 107.