Below normal rainfall?

To be sure, Halloween is next week and Thanksgiving is coming quickly. But the National Weather Service’s winter 2017-18 forecast is not supposed to be an “April Fool’s Joke.”

According to the NWS, “La Niña potentially emerging for the second year in a row as the biggest wildcard in how this year’s winter will shape up. La Niña has a 55- to 65-percent chance of developing before winter sets in.” Historically, a La Niña weather pattern will yield dry and below-normal precipitation in Southern California.

A La Niña was forecast for last winter. However, that is not what happened in Southern California — October 2016 to March 2017 was the wettest winter in Southern California history, according to Alex Tardy, warning coordination meteorologist at NWS’s San Diego office. Southern California received as much total rain as it had for the previous three years together.

But the current best forecasts — both observations and computer — suggest the probability of a drier-than-normal winter is greater than 60 percent through February and then neutral conditions will return in the early spring of 2018, according to Mike Halpert, deputy director of the National Oceanic and Atmospheric Administration’s Climate Prediction Center.

“If La Niña conditions develop, we predict it will be weak and potentially short-lived, but it could still shape the character of the upcoming winter,” said Halpert in a video. “With La Niña likely, we favor above-average temperatures across … the southern two-thirds of the United States … and below-average precipitation most likely across the entire Southern U.S.”

The NWS seasonal outlooks forecast the likelihood of above- or below-average temperatures and precipitation, but do not project seasonal snowfall accumulations. The agency stressed that snow forecasts are generally not predictable more than a week in advance because they depend upon the strength and track of winter storms.

The National Weather Service’s early winter 2018 forecast is for below-average precipitation in Southern California. The probability of less rain is 33 percent greater than a normal rainfall this winter. Map courtesy National Weather Service