Hydrologists Expect Below-average Streamflows in Northwest Montana
The low snow water equivalent levels in the Flathead River Basin and the Swan, Whitefish and Flathead mountain ranges will likely lead to below-average streamflows during spring runoff as the ski season winds down
By Maggie Dresser
Following a dry winter in northwest Montana that led to shallow snowpack levels in the Swan, Flathead and Whitefish mountain ranges, experts are forecasting below-average streamflows through July, says Eric Larson, a hydrologist with the USDA Natural Resources Conservation Service (NRCS).
The Flathead River Basin is expected to be about 85% of normal total runoff volume from April to July and Larson says it’s unlikely that spring precipitation will be able to compensate for the weak snowpack. The Sun-Marias-Teton Basin levels are expected to be at 65% of normal runoff, according to the April 1 water supply outlook report.
“It’s below-average across the board,” Larson said.
Snow water equivalent (SWE) levels in the Flathead Basin are at 76% of normal based on the median percentage between 1991 and 2020, as of April 8, while the Sun-Teton-Marias Basin levels are at 61% and the Kootenai Basin sits at 77%.
While Larson says snowpack levels are low this year, the Flathead Basin isn’t experiencing a historically low season, which he said dropped to 65% on April 1 in 2005.
Larson said weather stations across the state are seeing a SWE deficit, with several sites on the east side of the Continental Divide in the 10th percentile. Weather stations near Missoula, Great Falls, the Rocky Mountain Front and the southern Flathead Range have experienced near record-low precipitation since Oct. 1.
“All basins on the Rocky Mountain Front are still at 55 to 60 percent of normal snowpack and there are still some gains to be made there,” Larson said. “In terms of what it’s going to take to make a full recovery – it seems unlikely.”
The Flathead River Basin saw most of its precipitation accumulation in February, which was above average at 116%, according to SNOTEL sites, but precipitation in the early winter months were well below normal. In October, the monthly accumulation was 48% of normal and December was 76% of normal.
“Overall, the problem we are dealing with is a lack of precipitation from November through January,” Larson said. “It was decent in parts of February and March, but it just wasn’t enough to buffer that lack of precipitation.”
While snowpack levels typically peak between mid-April and mid-May, Larson said there is still time for snowpack levels to catch up, but there’s currently a 6- to 9-inch deficit in most locations in the Flathead.
On Flattop Mountain in Glacier National Park, the SWE level as of April 8 is at 36 inches, which is 9 inches below normal.
At the Mount Lockhart weather station, which sits at an elevation of 6,700 feet and feeds the Teton River, it typically peaks in mid-April at about 20 inches of SWE, which is currently at 13 inches.
In addition to the Teton River, other locations that Larson have identified as areas of concern are the Blackfoot, Clark Fork, Smith and Bighole rivers and users should expect low flows this season.
Despite the deficit, the Whitefish, Swan and Flathead ranges picked up additional precipitation in the first week of April, which experts say helped bring up SWE levels along with morale at Whitefish Mountain Resort on closing weekend.
Spring showers dropped more than a foot of new snow in Noisy Basin in the Swan Range and close to 10 inches on Big Mountain since April 4, bringing the snow depth to 89 inches. The resort accumulated 255 inches throughout the season.
Meanwhile, at Blacktail Mountain Ski Area near Lakeside, the snow stake reads 35 inches at the summit as of April 8 while the SWE level is only 59%. The ski area experienced a tumultuous start to the season with a delayed opening in mid-January and is scheduled to close on April 14.
While skiers across the state were forced to wait for widespread delayed openings and limited terrain access, some ski areas like Turner Mountain near Libby did not open for nearly the whole season while Teton Pass near Choteau did not open at all.
As the chairlifts quit turning in northwest Montana, the Flathead Avalanche Center is also winding down operations and forecaster Mark Dundas provided the final daily avalanche advisory for the 2023-2024 season on April 8. Snowpack updates will be issued every Tuesday and Friday by 5 p.m. through May 3.
