La Nina, warmth mix for tornadoes

WASHINGTON - 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.