Iowa’s tornado season is over for 2011 and forecasters say it was a fairly typical season in many ways, with a few surprises. National Weather Service meteorologist Brad Small says an even 50 tornadoes were confirmed in Iowa over the past year.
“Fifty is right about normal for the number of tornadoes in a season,” Small says. “The 30-year average is 47, so it’s really typical for a tornado season. They were clustered in three different primary events in March, April and another one in May.” He says most of this year’s twisters hit between 9 and 10 P.M.
“Tornadoes typically occur during peak heating of the day which is the late afternoon and early evening hours,” Small says. “We also had some tornadoes late in the night and early in the morning in July, not too many but that also occurs infrequently.”
A total of 20 twisters hit on a single day, April 9th, the day the Monona County town of Mapleton was hit, destroying about a hundred homes and businesses over 15 blocks. This year, no deaths were reported statewide from tornadoes but 16 people were hurt, 14 of them in the Mapleton tornado.
The average path cut by a tornado this year was three miles long but one tornado went nearly 30 miles. While Small says tornado season is essentially over for the year, tornadoes can hit during any month. “The chances are certainly diminishing and we’re all but over,” Small says. “You remember back in 2005, we had a tornado outbreak in November but we’re several weeks past that point. They hit Woodward and Stratford.”
Typically, he says temperatures need to at least be in the 60s with a dew point in the 50s for tornadoes to form. The last tornado of this year’s season was reported on July 11th. It marks the earliest cessation of tornado activity in the state since reliable records started being kept in 1980.