The white stuff on the way this winter could be more fog than snow.
Above-normal temperatures and below-normal precipitation from an expected weak El Niño weather pattern will likely dominate the months of December through February, according to the latest National Weather Service seasonal outlook. The winter will still get cold and wet, but probably not as dramatic as the last two La Niña winters.
“Watch for valley fog and dense fog days especially in December when the sun angle is at its lowest,” said National Weather Service forecaster Bob Nester. “We could also see flash freezes, where we get an inch or two of snow in Missoula in the nighttime and right afterward that stuff can freeze. That makes for pretty dangerous travel, generally during commute time.”
For the past week, warm, dry weather has been great for colorful larch and aspen foliage, but not so productive for big-game hunters. Montana Fish, Wildlife and Parks Region 2 Wildlife Manager Mike Thompson said game check stations in western Montana were recording lower-than-average success.
“Weather is always the driving factor in big game harvest, especially early in the season,” Thompson said. “When the weather is fairly warm and we have rain instead of snow, deer and elk don’t move much, making them harder to spot and track.”
Automatic snow-measuring stations in the Upper Clark Fork, Blackfoot and Bitterroot drainages all reported zero snowpack in the second week of hunting season for the first time since FWP started monitoring them in 2001.
El Niño/La Niña weather patterns shift back and forth every three to five years as a bulge of warm water off the western coast of South America expands and shrinks. In an El Niño year, Jet Stream winds that push Pacific moisture into North America get pulled south, causing wetter winters in the southwest United States and warmer conditions in the Pacific Northwest and western Canada. La Niña winds flow more to the north, drying the Southwest and feeding big snowfalls in the Northwest.
Historical records show consistently warmer temperatures in the Northwest during an El Niño year, but aren’t as reliable for precipitation and snowpack. Nester said the coming winter months could run four to six degrees warmer than average, especially in the central Idaho region.
“The December-to-February average snowfall is 25.4 inches in the Missoula area,” Nester said. “About 50 to 75 percent of normal is all we get in a weak El Niño. In the last two years, when we had a weak La Niña pattern, we got between 158 and 200 percent of normal snowfall. There’s quite the difference year to year.”
There can also be big differences day to day. An El Niño winter doesn’t mean the Northwest won’t experience an occasional arctic outbreak of super-cold air blowing down from Canada. And there’s a low possibility that this winter could be even snowier and colder than last year.
“Compared to last year when we had good snows and severe winter temperatures, this year doesn’t look like we'll have as severe a winter or the frequency of big winter events,” Nester said. “We could have a wet season but less snow.”