It’s quiet again in Tornado Alley – so quiet that researchers are digging deep into the record books for comparisons.
The estimated number of EF-1 or stronger tornadoes for the past 12 months is 217, according to National Severe Storms Laboratory tornado climatologist Harold Brooks. That’s “well below” the previous record of 247 for the fewest EF-1 or stronger tornadoes in a 12-month period, Brooks said.
May, which is historically the most active month for twisters in Tornado Alley, shows no signs of shaking things up.
“The pattern still looks pretty quiet,” Brooks said.
This is the slowest start to tornado season in Kansas in more than 15 years, according to the National Weather Service. There have been only four tornadoes reported in the Sunflower State through May 10, the fewest since 1997. The tornadoes that have developed were weak and short-lived.
The record for fewest tornadoes in May in all of the U.S. – 34 in 1952 – could be threatened this year, said Greg Carbin, warning coordination meteorologist for the Storm Prediction Center.
Iowa, meanwhile, is poised to break the state record for longest stretch without a reported tornado. As of Friday, it had been 351 days since a tornado touched down in the state. The current record is 355 days, set in the mid-1950s.
It’s not just the number of tornadoes that’s down across the nation. The number of people killed by tornadoes in the U.S. over the past 12 months is the lowest in more than a century.
Seven people were killed by tornadoes in the past 12 months, Brooks said. Though official tornado statistics go back only to 1950, he said, reliable records from The Tornado Project indicate that the seven who died over the past 12 months is the fewest since five died between September 1899 and August 1900.
“The data are reasonably good back to 1875, but it’s still possible that there are some missed fatalities, particularly as we go back farther in time,” Brooks wrote in the U.S. Severe Weather Blog.
Even if the numbers are blurred a bit by the mists of time, they still reflect a remarkably placid period for tornadoes.
“There is no trend” to explain the drastic drop in tornadoes in 2012 and 2013, Carbin said in an e-mail response to questions.
Last year’s silence was caused by a massive dome of high pressure that parked over the eastern two-thirds of the country for most of the year, weather researchers have said.
This year’s season has been muted by a ridge in the upper atmosphere that is bringing much higher-than-normal temperatures to Greenland and the north Atlantic, weather researcher and storm chaser Jon Davies said. A corresponding dip in the jet stream west of the ridge has brought colder air from the Northwest into the Great Plains, delivering snow and record cold deep into spring.
“A persistent northwest flow aloft pattern over the central U.S. in the early spring strongly discourages severe weather because of the colder temperatures and the associated difficulty the atmosphere has in bringing moisture northward from the Gulf of Mexico to fuel severe weather,” Davies said in an e-mail response to questions.
The lull follows the deadly and prolific tornado year of 2011, when nearly 1,700 tornadoes touched down – the second-most on record. The 550 people killed by tornadoes in 2011 was the fourth most on record and was the first time in more than half a century that the number topped 500, according to the National Oceanic and Atmospheric Administration.
Weather researchers are baffled by the dramatic swings and what could be driving them.
“There is nothing to indicate that the pattern is changing to dramatically alter the incredibly anemic severe weather season we have seen so far,” Carbin said.
The next week or so is shaping up to be somewhat more active than forecasters – and storm chasers – have seen so far this spring, he said.
“However, there does not appear to be a ‘game changer’ in the forecasts,” Carbin said.
Contributing: Associated Press