Streamflow forecast positive for Missions

As Montana enters spring and the typical snowpack peak season, the water supply outlook is currently good across most of the state. That can be attributed to consistent and mostly above normal precipitation this water year.

“March precipitation continued the trend of exceptional moisture received this year on the east side of the Continental Divide,” said Eric Larson, a water supply specialist for the Natural Resources Conservation Service.

East of the divide, March precipitation ranged from about 100% of normal in the Bighorn Mountains to nearly 170% of normal in the Jefferson River basin. The exception is the northern Rocky Mountain Front, which has had below normal precipitation this water year like the rest of northwest Montana.

“Montana was on the northern tier of the storms that tracked across California, Nevada, and Utah last month and provided record precipitation to those states. Those storms benefitted southwest Montana more than northwest Montana,” said Larson.

That trend has mainly been the case all year leaving the western Bitterroot, Lower Clark Fork, Kootenai, northern Flathead, and Rocky Mountain Front with below normal precipitation since Oct. 1. Snowpack percentages decreased from March 1 in the Flathead and Saint Mary River basins and all other major basins remained the same or saw an increase.

Snowpack percentages are about 80-90% in the northern Kootenai and northern Flathead River basins. Snowpack conditions are more favorable further south on the west side of the divide at about 90-105% of normal.

“The Flathead River basin is very large, and the basin-wide snowpack percentage is currently elevated by the deep snowpack in the southern Flathead region,” said Larson. The Upper Clark Fork River basin snowpack is more similar to east of the divide conditions at about 115% of normal.

“Mountain snowpack peak season is upon us and conditions are on track across most of the state except in northwest Montana which is generally lacking snow,” said Larson.

The snowpack usually peaks in early May at upper elevations and April at lower mountain elevations. Much of the lower mountain elevation snowpack east of the divide has already reached normal peak levels.

Elsewhere upper elevations are still generally two to three inches below normal peak levels. In those locations, normal precipitation during April will be necessary in order to reach normal peak snow water equivalent values at an ideal time. Well above normal April precipitation will be required in the furthest northwest part of Montana in order to reach typical peak levels this year.

West of the divide, streamflow forecasts are highest in the southern Mission Mountain region and the Upper Clark Fork River basin at about 110-130% of normal. Streamflow forecasts in the northern Kootenai and northern Flathead River basin are at about 70-90% of normal.

A full report of conditions on April 1 can be found in the monthly Water Supply Outlook Report available on the Montana Snow Survey website. In addition, real-time snow survey data can be found at nrcs.usda.gov/montana. Click on Montana Snow Survey Program.