The lingering La Niña climate cycle of cold tropical Pacific waters will impact your wintertime weather through March. The National Oceanic and Atmospheric Administration (NOAA) says the cooling of the ocean waters results in changes to the patterns of tropical rainfall from Indonesia to South America, which significantly affects the strength and location of the atmospheric jet stream over North America.

"La Niña will alter the strength and pattern of the Pacific jet stream over North America to give us a warm and dry winter in the southern half of the nation, but more snow and rain to the Pacific Northwest and Great Lakes," says D. James Baker, under secretary of commerce for oceans and atmosphere and NOAA administrator.

Drastic variations in temperature is another trait of La Niña. La Niña winters are characterized by temperature variability, or changes in the weekly mean temperatures as the season progresses. A season with little variability would have mean temperatures that changed little from week to week. A season with high variability will have some very warm weeks interspersed with very cold ones. Such temperature variability can increase health problems for livestock.

"We expect considerable month-to-month variation in temperature, rainfall and storminess in the central, northern and eastern states, which means days of warmer than normal temperatures followed by bouts of bitter cold," Mr. Baker says. "The cycling between the warmer El Niños and colder La Niñas can alter temperatures and rains to such an extent that they significantly disrupt U.S. agriculture. We're finding that last winter's La Niña may cause U.S. agriculture losses of more than $2 billion, which tops the $1.5 billion in agricultural damage from the 1997-98 El Niño cycle."

Meteorologists expect this winter to resemble last year's, and that dry conditions will be a significant concern for the central and southern U.S.