Winter is coming. And with it, a weather outlook impacted by weak, but persistent La Nina conditions in the equatorial Pacific.
El Ninos–like the record-breaking one that ended in June–occur when warm water from near Indonesia splashes over into the middle and eastern Pacific. La Ninas are the reverse: The same region gets cooler than usual. Two weeks ago, government forecasters finally declared that the region was showing undeniable La Nina characteristics. Yesterday, the National Oceanic and Atmospheric Administration released an updated analysis, predicting the La Nina has a 55 percent chance of lasting through the winter. “The official consensus probabilities favor La Nina to persist through January and February,” says Mike Halpert, Mike Halpert, deputy director of the agency’s Climate Prediction Center.
Mostly, this has to do with sea surface temperature. In the past four to six weeks, sea surface temperatures in the central eastern Pacific have been between a half and a full degree (Celsius) lower than historical average. This region of interest–called Nina 3.4 by weather wonks–spans the International Date Line, and extends about halfway to the Peruvian coastline.
Historically, La Ninas have meant bifurcated weather trends for the US. “We do expect above normal temperatures and below normal precipitation across much of southern US, and below normal temperatures and above normal precipitation across parts of the northern US,” says Halpert. For example, the 2007-2008 La Nina blanketed Canada with snow. And the southeast US had one of its worst droughts in recent history during the 2010-2011 event.
But Halpert says he won’t make specific predictions–no extension of California’s drought; no prolonged bout of babymakin’ weather in Wisconsin. “One of worst ways to make a forecast is do a simple analog, comparing one year to another,” he says. But dress warm anyway, sweet summer children. It’s always easier to remove a few layers than get caught in some foul weather because you put too much trust in your own sunny expectations.