La Niña Is Here To Stay: Cold Winter For Northern U.S.

La Niña, the weather phenomenon that is characterized by unusually cold ocean temperatures in the Equatorial Pacific, has arrived. Government forecasters say the event will continue through approximately February to April 2018, though the overall impact is predicted to be relatively weak.

In its winter weather outlook released in October, NOAA said La Niña had a 55 to 65 percent chance of developing before winter sets in. At the time, NOAA said as La Niña develops, it will be weak and potentially short-lived but could still shape the character of the upcoming winter.

On Thursday, NOAA said that with the formation of La Niña, the outlooks favor above-average temperatures and below-median precipitation across the southern United States. Across the Northern U.S., the outlooks favor below-average temperatures and above-median precipitation.

Since La Niña is predicted to be weak, NOAA says the impacts associated with it are still possible but "they become less likely."

"During La Nina winters, we often see greater than average snowfall around the Great Lakes and in the northern Rockies with less than average snowfall throughout the mid-Atlantic region," Mike Halpert, deputy director of the Weather Service's Climate Prediction Center, said in a video explaining the winter outlook in October. "Regardless of the outlook where you live, be prepared for typical winter hazards such as extreme cold and snowstorms."

La Niña is not the only factor that determines what the winter may look like, though forecasters say it is the biggest wildcard in how the year's winter will shape up.

The winter forecast is is probabilistic in nature, meaning other outcomes are possible, just less likely, according to forecasters.

Graphic courtesy NOAA