Flathead Basin snowpack all but gone, increased rain needed in June

Northwest Montana’s mountain snowpack is nearly melted out already, setting up a dire forecast of below normal water supply for rivers across the region.

“If it seems to you like the snow disappeared quickly this spring, you are not wrong,” said Eric Larson, USDA Natural Resources Conservation Service water supply specialist, in a press release Thursday.

According to Larson, warmer than normal temperatures in May resulted in rapid snowmelt. Weather stations across Montana melted out about 10-20 days earlier than normal. During the first several days of May and again in mid-month, high mountain elevations in Montana reached 70 degrees. Outside of those dates, daily average temperatures were closer to normal but still warmer than normal.

“Many SNOTEL stations across Montana experienced daily minimum temperatures above freezing for extended periods of time during May, which is what accelerated snowmelt to above normal rates,” said Larson.

For example, the snowpack totally melted out at Noisy Basin in the Swan Mountains on June 6. There was more than 80 inches of snow on the ground at the SNOTEL station at the beginning of May.

The snowpack at Flattop Mountain in Glacier National Park is all but gone, as well, with just 2 inches on the ground Thursday. Typically, that site holds snowpack well into July.

“Snowpack percentages dropped from near normal or above normal to less than 50% of normal in nearly all Montana basins since May first,” Larson added.

Almost 70% of NRCS snow monitoring stations measured on June 1 are snow free. For many, this is an earlier-than-normal melt out.

Energy Keepers, the Confederated Salish and Kootenai Tribes corporation that oversees the SKQ Dam in Polson, reported Monday that Flathead Lake is nearly at full pool, but warned that “lake sagging” is a possibility over the summer as water supply dwindles.

“Pretty much all snow has melted in the Flathead River Basin above Flathead Lake. Only tiny amounts of snow at extremely high elevation remain,” Energy Keepers officials reported.

The lake level could drop by as much as 12 inches over the summer in order to maintain minimum flows on the lower Flathead River, the corporation warned.

The U.S. Drought Monitor indicates Flathead County is in a moderate to severe drought — the worst conditions in the state.

Another drier-than-normal area extends from the northern Kootenai to the Saint Mary River basin, which already had a below normal snowpack and saw further decreases last month.

An exception to the dry trend is part of southwest Montana, which had a near record snowpack along the Idaho border. Several SNOTEL stations in that area still have an above normal snowpack that is currently tilting the basin-wide snowpack up to about 50-70% of normal in the Gallatin, Madison and Jefferson River basins.

Snowpack percentages in central and southwest Montana along the Idaho border were 110-140% of normal through May 1. The rest of the region was within about 10% of normal most of the year except part of northwest Montana that lacked snow overall this year.

Additionally, snow water equivalent peaks occurred at near normal levels on near normal dates this year in most locations. Snow water equivalent peaks are a strong indicator of overall snowmelt for the season, unfortunately, the bulk of that snowmelt occurred early this year.

ACTIVE SNOWMELT began over a month ago at all elevations in Montana. Mountain locations that held more snow than normal released a substantial amount of water last month and some rivers reported near record monthly streamflows. Rivers near Missoula, Butte, Helena, Bozeman, White Sulphur Springs and Billings experienced total monthly streamflows in May that were in their 80th percentile or greater.

“On May first, the NRCS May-July water supply forecasts estimated streamflows to be within about 10% of normal or greater for most of Montana. Since some of the snowmelt that was expected to occur in June already occurred in May, the recently published June-July forecasts have reduced volumes from what they would have been if May streamflows were normal,” said Larson.

June 1 seasonal water supply forecasts range from well above normal to well below normal in Montana.

Forecasts are lowest in northwest Montana and the northern Rocky Mountain Front where many streamflows are expected to be about 60-70% of normal. Some forecasts within that region, including all forks of the Flathead River, indicate streamflows will be less than 60% of normal through September.

The Beaverhead, Ruby, Smith, Boulder (Jefferson drainage), Musselshell and Madison rivers are expected to have streamflows over 120% of normal through September.

Most forecasts across the rest of Montana are expected to be about 80-90% of normal through September.

“Regardless of location, above normal precipitation would be ideal in June before heading into the drier months of summer, especially given the rate at which the snowpack melted out this year,” said Larson.