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March Precipitation Improves Streamflow Forecasts in Most Montana River Basins


BOZEMAN - Snow at higher elevations and rain in the valley yielded near to above average precipitation during March in all but one Montana River basin, according to data from the USDA’s Natural Resources Conservation Service (NRCS).

“The additional moisture increased most basin snowpack percentages this month to near to above normal, while the Sun-Teton-Marias continued to be overlooked by the passing storm systems,” said Lucas Zukiewicz, NRCS water supply specialist. In the Rocky Mountain Front, this year’s lack of snowfall has resulted in well below average snowpack in the Sun-Teton-Marias River basin—which is 70 percent of normal for April 1.

“As snowpack gradually melts, it provides water over a long period of time, and can be considered the largest reservoir in the state,” Zukiewicz said. Basins west of the Divide received 124 percent of average precipitation during March and river basins east of the Divide received 121 percent above average precipitation.

“Snowpack in the state typically peaks sometime during the coming month,” Zukiewicz said. “April 1 measurements are a good indicator of water available this coming runoff season.” Basins like the Sun-Teton-Marias, which are below normal in snowpack for this date, will need to see a major change in the weather patterns in order to add to this reservoir before spring melt and runoff.

April-June are critical across the state, and in some basins, the bulk of precipitation is received during this time period. Basins that are in good standing snowpack-wise can see further increases during this time and basins that are below normal can make some recovery. As of April 1, all of Montana’s major river basins have exceeded the amount of snow water at peak accumulation during this time last year.

“The snowpack in most of our basins is looking good, but last year was a great illustration of how important spring is to our reservoir system and rivers,” Zukiewicz said.

At this time last year, snowpack appeared to be in good shape before spring, but below average precipitation during March-June resulted in below average flows in our rivers last summer and fall. Given current conditions and assuming normal precipitation and temperatures over the next three months, this year looks to be different.

Long duration streamflow forecasts have improved from last month across the state and are near to slightly above average for the April-July time period. Most rivers expect to see near normal river flows this spring. However, some water users should be prepared for below average streamflows unless conditions change in the Sun-Teton-Marias and Tongue River basins.

“May 1 measurements and forecasts should give water users a good idea of the peak snowpack this year, and hopefully will show some recovery in those basins that are below normal,” Zukiewicz said.

Upper Clark Fork Basin

Snow trickled in relatively consistently in March in the Upper Clark Fork and the basin is currently at near normal conditions, which is slightly better than last year at this time. Last year on April 1 the basin wide snow water content was at 13.1 inches and appeared to have peaked several weeks earlier until a storm brought some much needed moisture. The basin wide snowpack peaked at 13.9 inches on April 17 last year.

This year the basin wide snow water content is currently at 14.8 inches and appears to still be accumulating at higher elevations. Rock Creek and Flint Creek have the highest percentage of normal snowpack in the basin at 107 percent and 101 percent, while the Blackfoot is the lowest at 88 percent.

The mid-March precipitation event that swept across most of western Montana wasn’t quite as significant in the Upper Clark Fork River basin as it was downstream in the Lower. Peterson Meadows SNOTEL received about one inch of precipitation during this event. March basin wide precipitation at SNOTEL sites reached 3.4 inches, which is 0.4 inches more than average. Overall, mountain SNOTEL sites received 106 percent of average precipitation for the month of March, while valley weather stations received 84 percent of average precipitation in the Bitterroot River basin.

Reservoir storage in the Upper Clark Fork River basin is currently at 100 percent of average.

Streamflow forecasts are generally near to above average across the basin for the April-July time period with the exception of the Blackfoot drainage which is slightly lower.

For more information and to view the whole report visit x-msg://11348/wps/PA_NRCSConsumption/download?cid=nrcseprd804206&ext=pdf


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