The National Weather Service in Missoula is expecting a weak La Niña to set in and cause above-average snowfall this winter in Montana.

From December through February, the average snowfall in Kalispell is 31.4 inches, but during a weak La Niña the average is 47.1 inches, said Bob Nester, senior meteorologist with the National Weather Service in Missoula.

“We had a La Niña last winter, but it died out over the summer and now it is redeveloping over the winter,” Nester said. “Every time we’ve had a weak La Niña, which we are expecting this year, we have had anywhere from 110-160 percent of normal [snowpack].”

A La Niña refers to the periodic cooling of ocean surface temperatures central and east-central Pacific Ocean. That affects rainfall patterns from Indonesia to South America, which in turn has an impact on weather patterns across the globe. The effect is usually strongest in the United States in the winter months. The process usually takes place every three to five years, but can sometimes occur in successive years, according to the National Weather Service.

The impact is generally more frequent storms, which helps boost annual snowfall and leads to above average snowpack.

A good chance of snow is in the forecast for later this week.

The National Weather Service says it is likely much of Northwest Montana will see snow between Wednesday and Saturday. The chance of precipitation is 90 percent on Wednesday and rises to 100 percent on Thursday in Kalispell.

Several inches of snowfall is expected in valley locations, with more than a foot possible over the higher terrain, including Marias, Lolo and Lookout passes.

Low temperatures in the Flathead Valley could dip into the teens on Thursday and Friday nights.

Dangerous travel, dangerous backcountry conditions and extremely cold temperatures are possible, the Weather Service warns.

In the more immediate term, the Weather Service predicts it will be about 44 degrees at 6 p.m. on Halloween with only a 17 percent chance of rain.

Peregrine Frissell can be reached at 758-4438 or pfrissell@dailyinterlake.com.