Add tornadoes — or rather, the lack of them — to the latest round of weather phenomena.
Iowa is on the verge of setting a record for most consecutive days without a EF1 tornado, according to the National Weather Service.
Nebraska is about 20 days from doing the same, said Greg Carbin, a meteorologist at the National Severe Storms Laboratory.
Nationwide, a record was recently set for the fewest EF1 tornadoes in a 12-month period, the National Severe Storms Laboratory said. An EF1 tornado has wind speeds of at least 86 mph.
The reason for so few tornadoes?
The weather pattern that established historic drought across the region last year also suffocated tornado development, said Mark Paquette, meteorologist with AccuWeather Inc., The World-Herald's weather consultant.
This year, we have opposite conditions but the same result, he said. The weather pattern that has allowed spring to be so cool and wet has robbed the atmosphere of the instability needed to spawn tornadoes, Paquette said.
Extreme weather has led to a number of records lately, including 2012 as Nebraska's hottest, driest year. This May is setting records for snowfall.
The last time Iowa had a confirmed tornado was May 24, 2012. If no tornadoes occur through Wednesday, the state will surpass the record of 355 days set at the end of April 1956, he said.
“To have gone this long without one is pretty extraordinary,” said John Lee, meteorologist for the National Weather Service in Des Moines.
Harold Brooks, research meteorologist for the National Severe Storms Laboratory, said preliminary numbers for May 2012 through April 2013 indicate that 197 tornadoes rated EF1 or stronger occurred in the United States. Lesser tornadoes weren't factored into his analysis because they cause little damage and may even have gone unnoticed in the past, so the historical record is considered suspect.
Also notable: The tornado drought is occurring two years after the worst year for total tornadoes. From May 2010 through June 2011, more than 1,000 EF1 or stronger tornadoes occurred, Brooks said.
The Nebraska record for consecutive days without a tornado is 371, ending May 3, 2003, Brooks said. As of today, Nebraska has gone 354 days since its last EF1 or stronger tornado.
Nebraska has had a handful of EF0 tornadoes — those with winds up to 85 mph — in the past year, according to the weather service. As is typically the case, they caused no noticeable damage.
The calm before the storms
Tornado droughts make weather experts nervous.
They worry that the public will become complacent.
“We're looking at a lull now, but the switch could go on at anytime,” said Ken Dewey, climatologist at the University of Nebraska-Lincoln. “That's something people need to know.”
Tornado season in Nebraska and Iowa typically kicks into gear in May and peaks in June.
The ingredient that has been missing this spring has been a flow of warm, moist air from the Gulf of Mexico, Dewey said.
Pent up for now, Gulf air eventually will cut loose and flow north, he said. When that happens, the potential for tornadoes will rise.
Annual tornado numbers are deceptive, Dewey said, because tornadoes occur in swarms.
High-number years typically get those numbers from intense tornado outbreaks.
Dewey points to May 22, 2004, as example.
About 60 tornadoes occurred across the region that day, including one that obliterated Hallam, Neb.
“We need to be prepared and on our toes,” Dewey said. “We live in Nebraska. The weather conditions change fast here.”
That's equally true for Iowa.
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