EXPLAINER: What came together to make deadly Alabama tornado

DENVER (AP) — A La Nina weather pattern, warm moist air coming from an unusually toasty Gulf of Mexico, likely juiced by climate change, and a decades long eastward shift of tornadoes came together to create the unusually early and deadly storm system that hit Alabama Thursday, meteorologists said.

And it may be the start of a bad tornado year, one expert worries.

Early signals, which could change, “indicate the overall pattern remains favorable for an above average tornadic year,” said Northern Illinois University meteorology professor Victor Gensini, who studies tornado patterns.

Gensini said his concern is mostly based on historic patterns and changes in atmospheric conditions that happen when a La Nina, which is a natural cooling of parts of the Pacific that changes weather worldwide, dissipates like it is forecast to do in a few months.

A NEEDED COMBINATION

For tornadoes to form, two big ingredients are needed that often aren’t at high enough levels at the same time: wet stormy instability and wind shear, which is a difference in wind speeds and directions at different altitudes.

At this time of year, “shear is a guarantee,” said Harold Brooks, a senior scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “What happens is when you get moisture you can have a (storm) system. That is the ingredient that is usually missing this time of year.”

The cold front was following a classic waviness in the jet stream — the atmospheric rivers that move weather systems — seen in La Nina winters, Gensini said. La Nina winters tend to produce more tornadoes and NOAA this week said preliminary numbers show 1,331 tornadoes in 2022, which was a La Nina year, 9% more than average.

“If you’re going to get tornadoes in January, this is...