What is "La Nina"?

[dan_s]

La Niña is the counterpart to El Niño, associated with cooler-than-average sea surface temperatures (SSTs) over the eastern equatorial Pacific. La Niña tends to favor an upper-level ridge over the northeast Pacific and a downstream trough over western North America. The classic effect on U.S. winters is to accentuate temperature contrasts between a chilly Northwest and a mild South, with an active polar jet stream leading to frequent storms and fronts.

In its last monthly outlook, issued October 12, NOAA gave 55-65% odds that La Niña will be in place this fall and winter. Most of the global models analyzed by the Australian Bureau of Meteorology on October 16 indicated La Niña conditions would develop. With trade winds beginning to strengthen in the last few days, and a large pool of cooler-than-average water lurking below the surface of the tropical Pacific, La Niña does appear to be a good bet for this winter.