But will La Niña last for long?
Cooler than normal sea surface temperatures indicative of La Niña conditions stretch across most of the eastern and central equatorial Pacific. (Source: earth.nullschool.net) After much anticipation, La Niña is finally here. During October and now into November, cooler than normal sea surface temperatures indicative of this weather-altering phenomenon have been stretching across most of the eastern and central equatorial Pacific Ocean. Here's a summary of the situation from today's update by the Climate Prediction Center of the National Weather Service:
. . . the forecaster consensus favors the continuation of weak La Niña conditions through December-February (DJF) 2016-17. At this time, the consensus favors La Niña to be short-lived, with ENSO-neutral favored beyond DJF.
The forecast pegs the odds of these conditions persisting through winter of 2016-17 at 55 percent. What might this mean weather-wise for North America?
Typical impacts of La Niña on U.S. winter temperature and precipitation. Such impacts have been associated with past episodes, but all impacts aren't seen with every episode. (Source: NOAA Climate.gov drawing by Fiona Martin.) La Niña typically tilts the odds in favor of below-average precipitation and above-average temperatures in the southern tier of the United States. Meanwhile, colder and wetter conditions are favored across the northern part of the nation, and large swaths of Canada as well. The Pacific Northwest already has been drenched in copious rainfall in recent weeks, with many records set for soggiest October. But it probably would be simplistic to pin this all on a weak La Niña, since other powerful climatic factors are likely at play as well.
Just what is La Niña? It is the flip side of the coin from El Niño — the other half of what's known as the "El Niño-Southern Oscillation, or ENSO. La Niña disrupts normal patterns of precipitation and atmospheric circulation in the tropical Pacific. Abnormally cold surface waters develop in the eastern and central equatorial Pacific. This tends to suppress cloudiness and rainfall there, especially during the Northern Hemisphere winter and spring. Meanwhile, far to the west, rainfall is enhanced over Indonesia, Malaysia and northern Australia.