La Nina Will Whip Up U.S. Winter Weather
Monastersky, R., Science News
Like a rude guest who refuses to leave, La Nina will hang around the tropical Pacific for several more months, upsetting U.S. weather for the second winter in a row, government forecasters predicted this week.
The climatologic opposite of El Nino, La Nina chills the waters of the equatorial Pacific Ocean and redirects the air currents carrying weather across North America. The current incarnation of La Nina developed in July 1998, following the strongest El Nino warming of this century.
"We have learned in recent years that local weather is determined by global climate," says D. James Baker, head of the National Oceanic and Atmospheric Administration (NOAA). "By looking at the global things that are happening, we can do a better job of forecasting what will happen locally."
The Pacific cooling has dwindled in recent months, but computer models forecast that it should strengthen over the winter and stick around at least through March, says Ed O'Lenic of NOANs Climate Prediction Center in Camp Springs, Md. Some other researchers, however, question whether this will be a La Nina-style winter.
A typical La Nina winter blows cold air over the northwestern states and northern Great Plains while warming much of the rest of the country. O'Lenic and his colleagues modified this prediction to take account of a global heating trend that has been boosting U.S. temperatures over the past 25 years.
The combination of both influences will keep most of the country warmer than usual this winter, with normal temperatures confined to the Northwest and northern Great Plains, predicts NOAA.
Whenever a La Nina appears, it tends to shove atmospheric winds into a looping route north of a high-pressure ridge over the northeast Pacific. …