The lingering “polar vortex” is getting tornado season off to a quiet start, but weather officials say they expect a surge of violent weather once the cold air finally retreats.
That may not happen until mid-April, they say, but after that – look out.
“We’re off to a slow start here in March” for tornadoes nationwide, said Paul Pastelok, head of long-range forecasting for AccuWeather.
At some point, he said, “you have to pay for it.”
AccuWeather officials expect a spike in violent weather around the nation in May and June. While May is historically the most active month for tornadoes, Pastelok said he expects the month to be even more active than normal.
Thus far, he said, this year mirrors the past two with its lower-than-normal number of tornadoes.
Data compiled by the National Oceanic and Atmospheric Administration’s Storm Prediction Center indicate there have been 49 tornadoes this year in the U.S. through March 13 – the lowest number in at least the past decade.
The primary reason, Pastelok said, is the arctic blasts have plunged so far south into the continental U.S. that they’ve cooled waters in the Gulf of Mexico. Warm, moist air from the gulf is a key ingredient in the formation of thunderstorms capable of producing tornadoes.
The jet stream’s persistent track far into the southern U.S. is blocking warm air from moving north and triggering thunderstorms. Until the jet stream shifts, Pastelok said, it will inhibit the spring storm season.
Predicting how active a given tornado season will be is next to impossible, said Larry Ruthi, meteorologist in charge of the Dodge City branch of the National Weather Service.
“I wouldn’t even want to guess” how many tornadoes will strike Kansas this year, he said. “We really have little skill in forecasting tornado seasons.”
So many things have to come together in just the right way for tornadoes to develop in the first place. Often, conditions can seem ideal and yet tornadoes never touch down – or they can seem marginal at best and yet tornadoes occur.
Nevertheless, “we’re due” for an active tornado season, Ruthi said.
He watches for weather patterns that can encourage or deflect conditions for tornado development. One component he’s noticed, he said, is that a pool of warm water in the northern Pacific is farther east than normal.
When that happens, he said, it can shift the jet stream in lower levels of the atmosphere to a track that delivers enhanced instability to the atmosphere over Kansas. That instability, called “shear,” measures how much winds are rotating at varying levels of the atmosphere. Shear is another key ingredient in the development of tornado-producing storms.
Given that pattern, Ruthi said, he expects a “hot and heavy” start to the severe weather season in Kansas in early May once warm, moist air from the Gulf of Mexico begins regularly feeding into the Central Plains.
“We may be pretty active for a while,” Ruthi said. “I think we will have a longer severe weather season than we did last year.”
That’s not saying much, considering tornado season in Kansas lasted “only about two weeks,” he said, “and then we were done.”
Actually, about five months passed between the first tornado of the year and the last, but the majority of tornadoes did occur in the latter half of May and the first few days of June. Only 56 tornadoes touched down in the state last year, slightly more than half the 10-year average of 109 and well below the average over the past 30 years of 81 per year.
Most of the tornadoes that did touch down in Kansas in 2013 were weak and short-lived. There were no fatalities and just one injury, and tornadoes touched down on only 15 days.