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What Caused the Deadly Tornadoes

WASHINGTON (AP) — All the right ingredients combined for Tuesday's killer tornadoes, especially warm moist air and a shifting weather pattern courtesy of the La Nina phenomenon. Just one thing was off: The calendar.

The Feb. 5 killer tornadoes — at least the 15th deadliest U.S. outbreak on record — had all the earmarks of a batch of twisters usually seen in March, said several meteorologists.

It was farther north than most February tornadoes and stronger, said Joseph Schaefer, director of the Storm Prediction Center in Norman, Okla.

Tornadoes do happen in February, but a study by Schaefer two years ago found that winter tornadoes in parts of the South occur more frequently and are stronger when there is a La Nina, a cooling of Pacific waters that is the flip side of the better known El Nino. In 1971, a deadlier February outbreak in the Mississippi Delta killed 121 people.

But Tuesday's weather violence, which killed at least 50 people, was noteworthy. February tornadoes usually pop up near the Gulf Coast, not in Kentucky or Tennessee, said University of Oklahoma meteorology professor Howard Bluestein.

Part of the explanation is record warmth. It was 84 degrees in Oklahoma before the storm front moved through on its path of destruction. On Tuesday, 97 weather stations broke or tied records in Arkansas, Alabama, Tennessee and Kentucky — the hardest-hit states.

Meteorologists are quick to say they cannot blame global warming. There is not enough good data over enough years with weather events as small as tornadoes, to draw such conclusions.

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