Severe weather outlook for spring

Jefferson City, MO (KFVS) Tornado Alley, the swath of prairie from Texas through Oklahoma, Kansas and Missouri famous for twisters, may see a largely calm tornado season this year.  But, a University of Missouri meteorologist says states in the northern plains could be in the line of fire.

The same dominant atmospheric phenomenon that spawned intense winter blizzards will likely shift spring and summer thunderstorm activity northward into Nebraska, Iowa, northern Illinois and Indiana, says Tony Lupo, professor of atmospheric science at the University of Missouri College of Agriculture, Food and Natural Resources.

That dominant climate factor is a strong La Niña.  La Niña occurs when cooler than normal water temperatures develop in the Equatorial Pacific Ocean.

The impact of La Niña is most clearly seen in wintertime.  Lupo says it tends to bring cold weather extremes to parts of the nation.  La Niña's opposite, El Niño, is associated with warmer water temperatures. In the continental U.S. during El Niño years, temperatures in the winter are generally warmer over the north, Midwest and east.

Both climate phenomena, which typically trade places every 3-6 years, influence weather patterns throughout the world.

Lupo says that La Niña tends to shift the jet stream patterns northward over the U.S.  In a La Niña season, the jet streams pick up warm Pacific moisture and direct their cargoes of warm and unstable air from Nebraska to the mid-Atlantic states.  Storm systems tend to follow these streams.

In a typical El Niño or neutral year, the jet stream travels farther south through Texas, Oklahoma and Kansas – Tornado Alley.

Lupo says Tornado Alley may see an unusually calm year for another reason. But atmospheric models predict a dryer than normal spring and summer, taking away the fuel for super-cell development.

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