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News Release

May 1, 2012, Record-Setting Temperatures Decrease Snowpac

Brian Domonkos

Record-Setting Temperatures Decrease Snowpack Across Majority of Montana

Bozeman--Cooler temperatures and average snowfall across Montana during the first half of April continued to build snowpack in most areas, but April’s second-half warming trend created substantial snow melt at most elevations causing rivers and streams to rise, according to May 1 snow survey data released by the USDA Natural Resources Conservation Service (NRCS). “The majority of our SNOTEL sites reached their maximum snow water equivalent during the first two weeks of April,” said , NRCS water supply specialist for Montana.

Although snowpack is actively melting, Domonkos said a few northwestern basins continue to be above average. The Kootenai, St. Mary’s and Milk, Flathead and Lower Clark Fork River basins continue to be at or slightly above average. Most other river basins have seen a decrease in average over the month and are slightly below average on May 1.

“The southwestern region of of Montana and the Lower Yellowstone River Basin felt the biggest effect from the unseasonably warm temperatures,” Domonkos said. “These basins experienced substantial melt during the second half of April, decreasing the basin averages to well below average and lowering stream flow prospects into spring and summer.”

Domonkos said Montana rivers typically peak during May and weather patterns over the next month will dictate the timing of river flows. “A return to warmer temperatures over the coming weeks could move our peak flows ahead of average, while cooler weather could help prolong river flows across the state into the summer,” he said.

Snow Water Content
River Basin Percent of Average Last Year Percent of Average April Percent Change
Columbia 100 241 -10
Kootenai, Montana 129 244 +2
Flathead, Montana 101 235 -5
Upper Clark Fork 80 226 -22
Bitterroot 84 299 -22
Lower Clark Fork 107 253 -5
Missouri 73 213 -20
Missouri Headwaters 70 205 -20
 - Jefferson 64 192 -25
 - Madison 78 224 -14
 - Gallatin 80 195 -7
Missouri Mainstem 82 224 -22
 - Headwaters Mainstem 72 220 -43
 - Smith-Judith-Musselshell 88 169 -12
 - Sun-Teton-Marias 86 349 -23
 - Milk (Bearpaw Mountains) 51 208 +26
St. Mary 120 218 +8
St. Mary and Milk 119 218 +20
Yellowstone 69 215 -19
 - Upper Yellowstone 78 240 -12
 - Lower Yellowstone 59 199 -27
Statewide 86 230 -15

If you encounter any problems with the files provided on this page, please contact Brian Domonkos at .

See the following text document for detailed basin snowpack information:

Basin-Wide Snowpack Summary (TXT; 64 KB)

Due to the above average snowpack melt during April, streamflow forecasts have been reduced in most watersheds. Only a select few basins have seen streamflow prospects increase as a result of above average April precipitation. “Again, this month’s forecasts vary greatly across the state so site specific forecasts will provide the best information,” Domonkos said.

Following are the averaged River Basin streamflow forecasts for the period May 1 through July 31. These forecasts assume near normal moisture and runoff conditions May through July.

Streamflow Forecasts
River Basin May to July this Year Percent of Average May to July Last Year Percent of Average
Columbia 102 155
-- Kootenai 118 145
-- Flathead 109 173
-- Upper Clark Fork 87 145
-- Bitterroot 95 134
-- Lower Clark Fork 105 153
Missouri 87 149
-- Jefferson 55 133
-- Madison 88 130
-- Gallatin 91 129
-- Missouri Mainstem 79 136
-- Smith-Judith-Musselshell 104 178
-- Sun-Teton-Marias 103 154
-- Milk 138 192
St. Mary 113 143
Yellowstone 82 140
-- Upper Yellowstone 92 142
-- Lower Yellowstone 72 138
Statewide 93 149

NOTE: The "May to July Last Year Percent of Average" column above is what was forecast last year, NOT what actually occurred.

See the following text document for detailed basin streamflow forecast information:

Provisional Water Supply Forecasts (TXT; 24 KB)


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