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Mountain Snowpack, Summer Streamflow Forecast Slightly Improved by February Snowfall

March 6, 2007

For More Information:
Roy Kaiser, 406-587-6991

Bozeman-- “February has been the best snowfall month so far this winter,” said Roy Kaiser, Natural Resources Conservation Service (NRCS) water supply specialist. “Mountain snowpack statewide increased seven percent over the course of the month.”

Comparing the snow water equivalent that accumulated during the month of February to the seasonal snow water equivalent peak illustrates this fact. For example, in the Columbia River basin the accumulated snow water equivalent was 118 percent of the average seasonal peak. In the St. Mary it was 100 percent of average, the Missouri was 131 percent of average, and the Yellowstone was 113 percent of average.

In addition, February mountain precipitation was 105 percent of average and water year precipitation was 101 percent of average. February mountain precipitation in the Columbia River basin was 93 percent of average, Missouri was 118 percent of average, St. Mary was 73 percent of average, and Yellowstone was 111 percent of average.

March 1 is more than three quarters of the way through the main snowfall period. There are normally about four to six weeks remaining until the seasonal snowpack peak is reached. On March 1, accumulated snow water equivalent west of the Continental Divide was 90 percent of average and east of the Divide was 84 percent of average.

“March is a critical snowfall month. Having an average to above average March snowfall will build on a very good February and continue to bring snowpacks closer to average,” said Kaiser.

Statewide, mountain snow water equivalent was 87 percent of average and 84 of last year at this time. West of the Continental Divide, snowpack was 90 percent of average and 87 percent of last year and east of the Continental Divide, snowpack was 84 percent of average and 85 percent of last year.

Snow Water Equivalent
River Basin Percent of Average Percent of Last Year February Percent Change
Columbia 90 87 +5
--Kootenai, Montana 99 93 0
--Kootenay, Canada 109 122 -3
--Flathead, Montana 89 84 +5
--Flathead, Canada 102 95 +4
--Upper Clark Fork 85 89 +8
--Bitterroot 85 79 +5
--Lower Clark Fork 93 86 +5
Missouri 87 84 +16
--Missouri Headwaters 82 77 +11
----Jefferson 83 81 +9
----Madison 79 74 +11
----Gallatin 80 72 +16
--Missouri Mainstem 98 97 +15
----Headwaters Mainstem 93 89 +11
----Smith-Judith-Musselshell 102 88 +23
----Sun-Teton-Marias 90 97 0
----Milk 136 155 ---
------Bearpaw Mountains 115 101 +42
------Cypress Hills, Canada 152 240 +48
St. Mary 87 85 +1
St. Mary & Milk 102 105 +20
Yellowstone 79 85 +9
--Upper Yellowstone 81 79 +11
--Lower Yellowstone 77 92 +7
Statewide 87 84 +7

Streamflows across Montana are forecast to average 73 to 87 percent of normal. West of the Continental Divide, streamflows are forecast to average 83 to 93 percent of normal and east of the Continental Divide, streamflows are forecast to average 66 to 83 percent of normal.

Below are averaged streamflow forecasts, by river basin, for the period April 1 through July 31. These forecasts assume normal spring conditions and do not account for well below average (70 percent or less) or above average (110 percent or more) snowmelt or spring rain. Specific forecast probabilities are available in each individual River Basin Report on the Montana NRCS web page.

Streamflow Forecasts
River Basin April-July This Year Percent of Average April-July Last Year Percent of Average
Columbia 83 to 93 89 to 100
--Kootenai 88 to 96 90 to 99
--Flathead 86 to 94 95 to 104
--Upper Clark Fork 79 to 94 78 to 94
--Bitterroot 79 to 88 103 to 112
--Lower Clark Fork 83 to 93 89 to 98
Missouri 64 to 83 78 to 98
--Jefferson 56 to 76 70 to 91
--Madison 77 to 85 103 to 111
--Gallatin 74 to 84 99 to 110
--Missouri Mainstem 67 to 80 87 to 102
--Smith-Judith-Musselshell 48 to 73 99 to 119
--Sun-Teton-Marias 76 to 95 68 to 86
--Milk 67 to 101 46 to 86
St. Mary 92 to 98 85 to 92
Yellowstone 69 to 81 88 to 100
--Upper Yellowstone 76 to 87 98 to 108
--Lower Yellowstone 60 to 74 75 to 89
Statewide 73 to 87 84 to 99

NOTE: The April-July Last Year Percent of Average column above is what was forecast last year, not what actually occurred.

The NRCS snow survey and water supply forecast program provides detailed snow water content, streamflow forecast, and climate data for Montana by evaluating data collected by a series of manual and automated snow survey sites located in the mountains of the state. Visit the NRCS Snow Survey and Water Supply Forecast Program website for more information.

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