Forecast indicates La Niña will persist
Ski hills and snow enthusiasts in Northwest Montana are cautiously optimistic that a developing La Niña system will consistently dump powder for the next few months, but the periodic weather cycle has had an inconsistent impact on winters over the past two decades.
Defined as a period following at least three months of cooling sea-surface temperatures along the equator, La Niña pushes the jet stream north, typically pushing above-average moisture into the Northern Rockies. Winter temperatures also usually stay below average, setting up the conditions for plenty of snow.
While sea-surface temperatures have been falling in the East-Central Pacific during the last couple months, the anticipated La Niña system is not yet official.
“When we do have La Niña in effect, it tends to mean above-normal snowpack, particularly for the mountains, but often for the valleys as well,” said Jennifer Kitsmiller, a meteorologist with the National Weather Service office in Missoula. “For all intents and purposes, we’re calling it La Niña.”
Recent La Niña systems have corresponded with above-average snowfall on Big Mountain overall, but individual winters have been hit-or-miss.
According to data from Whitefish Mountain Ski Resort, end-of-season snowfall totals average 353 inches. The last six La Niña seasons have mostly hovered around that total, although the monster snow year of 2007-08 dumped an impressive 426 inches at the resort. More recently, the 2011-12 La Niña weather pattern only dropped 303 inches.
“How much [snowfall] varies from La Niña year to La Niña year,” Kitsmiller said.
“Moisture is very important for how the atmosphere behaves, and one of the biggest sources of moisture is from the ocean. ... [But] other oscillations occur in other oceanic regions that then play into each other.”
The weather phenomenon’s unpredictable effects also play out on the valley floors.
Many Flathead Valley residents remember the brutal winter of 1996-97, which started with more than 4 feet of snow falling in November, a month averaging just 9 inches of snow in Kalispell.
The Dec. 1, 1996 front page of the Daily Inter Lake described “desperate customers scrambling for everything from snow blowers to boots” and a shipment of 23 snow blowers at Costco “triggering a feeding frenzy.” By Christmas Eve, the paper reported traffic snarled by 8-foot snowdrifts blocking the road.
From November through March that winter, 139 inches of snow fell in the valley, compared with an average of 51.9 inches. But that wasn’t even a La Niña year. That weather system did appear the following winter, dropping a less impressive, but still above-average, 75.9 inches.
A strong La Niña system stayed in place for three consecutive winters, dropping significant snow beginning with the 1999-2000 season. Then the last three La Niña patterns were less impressive, with typical to below-average snowfall.
As for this winter, the National Oceanic and Atmospheric Administration’s Nov. 28 outlook gives the weather system a 55 percent chance of continuing through the season.
According to the agency’s most recent three-month outlook, Western Montana, along with the rest of state, has a 40 percent chance of above-normal precipitation through February 2017.
Overall temperatures are more likely to hew to the average.
“The overall consensus is for a weak La Niña,” Kitsmiller said. “Conditions are favored through about February, then by March they will start fizzling out toward more neutral conditions.”