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News Release

As Montana Snowpack Transitions Into Spring, Runoff Should Be Monitored

Lucas Zukiewicz

BOZEMAN, Mont., May 7, 2014–Data from the USDA Natural Resources Conservation Service (NRCS) SNOTEL (SnoTelemetry) sites show Montana’s April snowfall did not match the well above average precipitation experienced during February and March, but because Montana has not yet seen a major shift in weather patterns, snowmelt has been delayed and basin percentages of normal remain high.

Data shows most basins in the state exhibited peak snow water equivalent during the beginning and middle part of April, while some basins in southwest Montana and along the Continental Divide exhibited peaks at the end of the month. According to Lucas Zukiewicz, NRCS hydrologist, some snowmelt has occurred at lower to mid elevations, but higher elevations in the basins have seen little melt during the month, delaying when the bulk of snowmelt runoff enters river systems. “Assuming normal climatic conditions in the upcoming weeks, more advanced melt rates should begin to occur as days get longer with more solar influence and temperatures get warmer," Zukiewicz said.

Statewide SNOTEL and snow course data reported 155 percent of normal for May 1 and 149 percent of last year at this time. The Bitterroot River Basin currently has the highest basin percentage of normal in the state, indicating 188 percent of normal for May 1 and 199 percent of last year at this time. “Worth noting this month are the Missouri Mainstem, Tongue, and Powder River basins which reported the highest daily snow water equivalent values (SWE) since 1981,” Zukiewicz said. “However, the 2014 peak snow water equivalent did not surpass those recorded 1997 and 2011.”

Snow Water Content
River Basin May 1 Percent of Median Percent of Last Year
Columbia 159 148
Kootenai, Montana 145 126
Flathead, Montana 156 138
Upper Clark Fork 162 170
Bitterroot 188 199
Lower Clark Fork 164 138
Missouri 150 153
Missouri Headwaters 142 149
- Jefferson 143 159
- Madison 135 141
- Gallatin 148 142
Missouri Mainstem 172 164
- Headwaters Mainstem 180 186
- Smith-Judith-Musselshell 158 154
- Sun-Teton-Marias 178 160
- Milk (Bearpaw Mountains) 0 0
St. Mary 138 116
St. Mary and Milk 136 115
Yellowstone 157 153
Upper Yellowstone 166 166
Lower Yellowstone 149 144
Statewide 155 149

Zukiewicz said if snowmelt continues to be delayed in the mountains, the basin percentages of normal will continue to increase. “This time of year the daily normal value that we compare current snow water equivalent values to is decreasing as it generally represents a melting snowpack. If basin snow water equivalent decreases at a slower rate than the daily normal, or increases while the normal decreases, the basin percentages climb. Since the peak may have been observed in many of the basins, the basin percentages are indicating that there is a substantial amount of snow water left in the mountains for runoff this spring,” he said.

While April precipitation varied across the state, the statewide precipitation for April was slightly below average at 93 percent. The far western basins along the Idaho border and central part of Montana received well below average precipitation for the month. The overall water year-to-date precipitation totals since Oct. 1 still reflect above average precipitation (to date) in most basins. The statewide precipitation is currently 116 percent of average, and 115 percent of last year at this time.

Streamflow Forecasts

Streamflow prospects continue to be well above average in most parts of the state. Statewide streamflow forecasts indicate 146 percent of the average May-July flows, and 152 percent of what was experienced last year. The Smith-Judith-Musselshell combined river basin continues to have the highest percentage of average May-July flows using the 50 percent exceedance forecast at 182 percent of average. The extreme headwaters of the Jefferson River basin continue to have the lowest forecasts in the state indicating 72 percent of average May-July flows for Lima Reservoir inflow and 80 percent for Clark Canyon inflow. For greater detail on spring runoff forecasts, consult the May 1 Water Supply Outlook Report.

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

May-July Streamflow Forecast Period
River Basin Forecast as Percent of Average This Year Forecast as Percent of Last Year Streamflow
Columbia 148 130
Kootenai 122 132
Flathead 129 117
Upper Clark Fork 160 203
Bitterroot 158 207
Lower Clark Fork 144 155
Missouri 143 189
Missouri Headwaters 130 246
- Jefferson 134 349
- Madison 117 168
- Gallatin 136 189
Missouri Mainstem 145 182
Headwaters Mainstem 146 184
Smith-Judith-Musselshell 182 341
Sun-Teton-Marias 137 147
St. Mary 109 99
Milk (May-Sept. % median) 108 121
Yellowstone 146 191
Upper Yellowstone 142 177
Lower Yellowstone 149 202
Statewide 146 152