She’s back: La Niña returns bringing potentially volatile winter temps with her

Don’t be surprised by mild temperatures early in the season

She’s back.

La Niña, last winter’s dominant climate pattern, will recur. The National Oceanic and Atmospheric Administration’s outlook for December through February indicates a La Niña winter for the second year in a row.

La Niña, Spanish for “the girl,” is characterized by unpredictable weather, according to experts, so don’t be surprised by mild temperatures early in the season. But make sure to keep snow boots, woolen gloves and snuggly scarves handy for a suburban cold snap during January and February.

“La Niña winters are known for pretty volatile temperatures,” said Ricky Castro, a meteorologist with the National Weather Service in Romeoville.

“That means our area is a battleground-type zone,” said Castro, explaining the upcoming season could consist of “episodes of substantially warm (weather) or really deep cold as well.”

To that end, Castro recalls last year which began with mild weather followed by five or six weeks of cold and snow from late January to mid-February.

“Any winter often has dueling periods of warm and cold,” said Castro. “The volatility of the temperature pattern in La Niña tends to be higher variability.”

During the 1998-99 winter La Niña, temperatures were above normal overall up until the New Year’s blizzard, which occurred Jan. 1 to 3 and was followed by two weeks of bitter cold.

According to NOAA, La Niña results from cooler than average sea surface temperatures in the tropical Pacific.

The belt of colder temperatures affects jet stream patterns across North America, the stronger effects of which are felt during the colder months, Castro said.

That translates to warmer than average winter season conditions projected across the southern U.S. and much of the eastern U.S. By comparison, NOAA predicts below average temperatures for southeast Alaska, the Pacific Northwest and eastward to the northern Plains.

The upper Mississippi Valley and parts of the Great Lakes region have equal chances for below-, near- or above-average temperatures, according to the agency’s report released Oct. 21.

As for precipitation, the Great Lakes, Pacific Northwest, northern Rockies and parts of the Ohio Valley and western Alaska have the greatest chances for wetter-than-average conditions, according to NOAA.

Castro cautions that a projection of above-normal precipitation is not a snowfall forecast.

La Niña “tends to favor higher snow amounts, but snowfall is such a variable thing,” he said.

While above-normal precipitation could statistically favor more snow -- and meteorologists point out some La Niña winters have been accompanied by “memorable snow events” -- that’s not always the case, according to the NWS.

“The predominant storm track and alignment with sufficiently cold air will dictate seasonal snowfall,” according to the NWS.