NOAA’s Climate Prediction Center has issued its forecast for the 2017-18 winter season and, for the second year in a row, La Niña is poised to be a major factor in how the season shapes up. In general, the forecasters are predicting a cooler, wetter north, and a warmer, drier south.
It’s difficult to know what the weather will be like next week, let alone the next several months, but thanks to years of accumulated weather data and computer-powered climate modeling, meteorologists can make a pretty good stab at it. This year however, their predictions are complicated by one major unknown: La Niña.
The NOAA says there’s about a 55-65 percent chance of La Niña emerging before winter sets in, but if it does, it’ll likely be weak and short-lived. La Niña is a recurring weather phenomenon that’s related to El Niño, and is characterized by sea surface temperature decreases in the Eastern Central Pacific Ocean. Last year, it arrived in early November, producing above average precipitation and colder than average temperatures along the northern tip of the United States, and drier conditions across the South. This coming winter could feature a repeat of 2016-17.
“La Niña conditions often occur two winters in a row, and we may see a follow-up this winter to the brief La Niña of late 2016,” Weather Underground meteorologist Bob Henson explained to Gizmodo. “La Niña tends to intensify temperature contrasts across the US, so northern winters tend to be a bit colder than average and southern winters even milder than average.”
But this is all playing out against a backdrop of US climate that’s being warmed by greenhouse gases, cautions Henson. “So I wouldn’t look for a winter-long stretch of brutal cold in the Northwest, Midwest, and Northeast,” he says. Henson believes it’s more likely that Americans will see a few strong pulses of Arctic air, but interspersed with some distinct warm spells. At the same time, he predicts that the South and Southwest have a shot at experiencing a consistently mid-to-warm winter.
NOAA’s Climate Prediction Center expects wetter-than-average conditions across most of the northern US this coming winter, from the northern Rockies all the way to the eastern Great Lakes and the Ohio Valley. Same goes for Hawaii and western and northern Alaska.
Meanwhile, the entire southern US should expect conditions that are drier than normal. Drought is, unfortunately, likely to persist along the northern plains states, with some improvements possibly happening further west. The NOAA says drought conditions could emerge in some areas of the south, primarily regions that missed the rainfall associated with the slew of hurricanes that came through this past summer.
Temperatures are expected to be warmer than average across the southern two-thirds of the continental US, and also along the East Coast, Hawaii, and western and northern Alaska. It’ll likely be colder than average along the US northern tier from Minnesota to the Pacific Northwest, and in southeastern Alaska. The rest of the US falls into the so-called “equal change” category, which is exactly as it sounds: These areas have an equal chance for either above, normal, or below temperatures and precipitation (NOAA meteorologists don’t have enough data at the moment to shift the odds).
While the NOAA makes long term predictions about precipitation and other weather conditions, it doesn’t make a claim about the frequency or severity of winter storms, including snowstorms.
“While the last two winters featured above-average temperatures over much of the nation, significant snowstorms still impacted different parts of the country,” writes the NOAA in a release. “Snow forecasts are generally not predictable more than a week in advance because they depend upon the strength and track of winter storms.”
The NOAA will update its forecast in mid-November, at which time we should know more about La Niña, and other weather-making patterns.