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News Release

Snowmelt-Driven River Flows Peak During the Month of May

Contact:
Lucas Zukiewicz
406-587-6843


BOZEMAN, Mont., June 9, 2014–Snowmelt increased river flows across the state in May, according to data from the USDA Natural Resources Conservation Service (NRCS).  After nearly record-breaking snowfall during February and March, weather patterns in April and May helped transition the snowpack into runoff.  Many rivers reached the snowmelt-driven peak volumes without reaching flood stage.

“The water faucet from the mountains really turned on in May,”  said Lucas Zukiewicz, NRCS water supply specialist for Montana.  “While our peak flows from snowmelt likely occurred at the end of May, we should still keep an eye on rivers if precipitation occurs.”

Beginning in the middle and end of April, snowmelt decreased lower elevation snowpacks; warm weather at the beginning of May started the melt at mid-elevations; and after mid-May, snowmelt occurred at all elevations. The melt of different elevations over a few weeks limited the large volume of snow water, which accumulates in the winter snowpack, to enter the river systems.  Snow water entered rivers in small waves, instead of all at once.

Snow Water Content
River Basin June 1 Percent of Median June 1 Percent Remaining Percent of Last Year
Columbia 169 43 193
Kootenai, Montana 173 42 178
Flathead, Montana 159 53 154
Upper Clark Fork 159 44 240
Bitterroot 192 32 507
Lower Clark Fork 230 38 213
Missouri 129 31 192
Missouri Headwaters 123 35 184
- Jefferson 124 35 186
- Madison 108 40 171
- Gallatin 132 38 164
Missouri Mainstem 152 24 235
- Headwaters Mainstem 136 29 403
- Smith-Judith-Musselshell 118 17 193
- Sun-Teton-Marias 189 35 221
- Milk (Bearpaw Mountains) 0 0 0
St. Mary 144 60 127
St. Mary and Milk 144 55 127
Yellowstone 144 38 209
Upper Yellowstone 140 44 214
Lower Yellowstone 149 31 229
Statewide 148 30 195

 

Statewide snowpack is currently 148 percent of normal and 195 percent of last year at this time.  As of June 1, 71 SNOTEL sites at low and some mid-elevations have melted across the Montana Data Collection Office (including WY and SD). 50 to 75 percent of the peak snow water equivalent at higher elevation SNOTEL sites still have not entered river systems. This snow water will help to sustain flows through spring and into summer.

Due to the amount of snow during the winter, water year-to-date precipitation has been above average since October 1. Statewide water year-to-date precipitation is 108 percent of average and 103 percent of last year. “All of the basins in Montana received below to well-below average precipitation for the month of May,” Zukiewicz said.  “This kept river flows mostly influenced by snowmelt runoff.”

Streamflow

Streamflow response to snowmelt has been a best-case scenario this spring.  However, if precipitation events occur, they could amplify high-elevation snowmelt and rapidly add water to already swollen rivers.

Assuming normal conditions in the future, many rivers experienced their snowmelt-driven peaks across the state at the end of May.  Because a large volume of the snow water was moved during May streamflow, forecasts have dropped slightly since May 1.  Statewide streamflow is forecasted to be 128 percent of average for the June 1 – July 31 time period and 154 percent of last year.

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

June-July Streamflow Forecast Period
River Basin Forecast as Percent of Average This Year Forecast as Percent of Last Year Streamflow
Columbia 124 133
Kootenai 110 91
Flathead 130 134
Upper Clark Fork 114 172
Bitterroot 136 217
Lower Clark Fork 128 161
Missouri 129 174
Missouri Headwaters 123 217
- Jefferson 125 428
- Madison 109 176
- Gallatin 132 197
Missouri Mainstem 130 165
Headwaters Mainstem 130 164
Smith-Judith-Musselshell 240 269
Sun-Teton-Marias 132 166
St. Mary 110 104
Yellowstone 135 195
Upper Yellowstone 134 185
Lower Yellowstone 134 204
Statewide 128 154

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