Snowpack dwindles

For the second straight month Montana has seen a decline in snowpack percentages of normal due to the lack of significant snowfall and above normal temperatures, according to snowpack data from the USDA Natural Resources Conservation Service (NRCS).

Basins west of the Continental Divide have seen the most substantial change since Feb. 1 with basin snowpack percentages declining 9 to 16 percent during the month. East of the Continental Divide most of the basins saw a decline in snowpack percentages, but not to the extent of the western part of the state. One basin that feeds Montana rivers from the south in Wyoming saw an increase in snowpack during the month (Lower Yellowstone).

“As disappointing as the declines and below normal snowpack percentages may be, Montana is in good shape snowpack wise compared to most of the West this water year,” said Lucas Zukiewicz, NRCS water supply specialist for Montana.

What do these changes mean for water users across the state as we approach runoff season this spring? “It is important to remember that many basins were above to well above normal on January 1^st, and the abundant early season snowfall has helped to keep many of our basin percentages near normal for this time on March 1^st,” Zukiewicz said. “Winter is not over; many basins east of the Divide are favored in the coming months regarding snowfall, and a pattern change would certainly be welcome at this point.”

A few basins have been below normal for the entire water year and February didn’t improve conditions in those basins. West of the Divide, the Kootenai and Lower Clark Fork River basins are well below normal for this time of year, 60% and 65% respectively. East of the Divide, the St. Mary-Milk basin and the Madison River basin are below normal, 65% and 80% respectively. Zukiewicz said in order for these basins to recover before spring runoff a major pattern change will be needed in order to receive near average water yield from the snowpack.

Streamflow Forecasts

Zukiewicz said if the snowpack numbers decline through the month, generally streamflow prospects will follow suit. “This month our forecasts have dropped in almost every basin due to the declining basin percentages of normal snowpack,” he said. Streamflows have declined the most west of the Continental Divide dropping 2 to 12 percent over the month. While they have fallen slightly, most forecasts west of the Divide are still near normal for the April-July time period.

East of the Divide April-July streamflow prospects are slightly lower and are slightly below average for the period. In this region Zukiewicz said there are a few sub-basins of concern, the Red Rocks Valley feeding Lima Reservoir and the Ruby River Valley feeding Ruby Reservoir. Both of these basins have been well below normal for the entire year and streamflow forecasts reflect the lack of snow so far this season.

“There is still two to three months left for snowpack to accumulate and the future snowfall, or lack therof, will have an impact on the streamflows this spring,” Zukiewicz said. “It is not too late to make improvements before snowmelt, but Old Man Winter better make his appearance again sooner than later.”

Below are the averaged River Basin streamflow forecasts for the period April 1 through July 31. THESE FORECASTS ASSUME NEAR NORMAL MOISTURE AND RUNOFF CONDITIONS FEBRUARY THROUGH JULY.

For detailed information on individual basin conditions refer to the March 1 Water Supply Outlook Report.