DENVER (AP) — La Niña weather patterns, warm, moist air from an unusually hot Gulf of Mexico likely driven by climate change, and years of eastward drift of tornadoes have combined to create an unusually early and deadly storm system that has made landfall, meteorologists say. , Thursday in Alabama.
And this could be the start of a bad tornado year, one expert fears.
Early signals that could change “indicate that the overall picture remains favorable for an above-average tornado year,” said Northern Illinois University meteorology professor Victor Gencini, who studies tornado patterns.
Jencini said his concern is largely based on historical patterns and changes in atmospheric conditions that occur when La Niña, the natural cooling of parts of the Pacific that changes weather around the world, is predicted to dissipate in a few months.
REQUIRED COMBINATION
Tornado formation requires two important ingredients that are often not high enough at the same time: wet storm instability and wind shear, which is the difference in wind speed and direction at different heights.
At this time of year, “shift is a guarantee,” said Harold Brooks, senior scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “What happens is that when you get moisture, you can have a (storm) system. It’s something that’s usually missing at this time of year.”
The cold front followed the classic undulations of the jet stream — atmospheric rivers that move weather systems — seen in La Niña in winter, Jencini said. La Niña winters tend to produce more tornadoes, and this week NOAA said preliminary data shows 1,331 tornadoes in 2022, which was a La Niña year, up 9% from the average.
“If you’re going to get tornadoes in January, that’s the type of setup that’s going to cause them,” Gencini said.
Still, without moisture there is no tornado.
WARM HUMID AIR
Gencini said humidity measurements in Alabama were about twice as high as they should be at this time of year, and more like May in Tornado Alley, an area known for its tornado-proneness stretching from Texas to South Dakota. That’s more than enough for a tornado.
Warm, moist air comes in from the Gulf of Mexico, and he said, “This is a signal of climate change.”
Jensini pointed to NOAA measurements of water temperatures across the Persian Gulf on a computer screen and said, “Look at that number. 70 (21 degrees Celsius). 70. 70. This is ridiculous. This is well above average for this time of year. This nearby warm water filled the air with sap.
“It’s a lot of the La Niña-type system you’d expect, but it’s complemented by abnormally high sea surface temperatures in the Gulf of Mexico,” Jensini said.
Gencini said that warm, moist air collides with a cold front and rises like a ramp, and mixing begins, which creates a tornado.
TORNADO IN THE EAST
Over the past few decades, a new pattern of tornado activity has emerged.
There are fewer tornadoes in Tornado Alley and more tornadoes east of the Mississippi River in the Southeast, a 2018 study by Jensini and Brooks found.
Tornado activity increases most in Mississippi, Arkansas, Tennessee, Louisiana, Alabama, Kentucky, Missouri, Illinois, Indiana, Wisconsin, Iowa, and parts of Ohio and Michigan. The biggest decline in tornadoes is in Texas, but even with this decline, Texas still receives the most tornadoes of any state.
Gencini said his lab is trying to figure out why that is this summer.
MORE VULNERABILITY
An unfortunate side effect of tornadoes moving further east is that they move from less populated areas to more crowded ones, Brooks and Jensini said.
In Tornado Alley, a tornado can spread for miles and miles without hitting anything or anyone, and so won’t be a problem, according to Brooks. But this is not entirely true in the East. People and buildings interfere.
And the people along the way are more vulnerable.
“There’s more poverty in the Southeast, more mobile homes,” one of the most dangerous places during a tornado, Brooks said.
Also, due to storm tracks or the routes that storms follow due to wind and weather conditions, the further east a tornado strikes, the more likely it is that they will strike later in the day and even at night when people sleeping or not listening to warnings. Gensini said.
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