Given the lack of precipitation from November through most of January in Montana, above normal precipitation was needed over the last couple of months. "February did provide well above normal precipitation to nearly all of Montana and those weather patterns continued into the first week of March across the state," said Eric Larson, USDA Natural Resources Conservation Service (NRCS) Water Supply Specialist. What seemed to be the beginning of a potential recovery only tapered off in many basins. Overall, precipitation during March was above normal in southwest and southern Montana, but below normal elsewhere.
"The good news is the southern Absaroka and Wind River region has received near normal precipitation this season, as a result the Bighorn River basin snowpack is 95% of normal," said Larson. In contrast, snowpack percentages are currently about 55-65% of normal in the Sun-Teton-Marias, Smith-Judith-Musselshell, Upper Clark Fork, and Powder River basins. All other river basins in Montana have about a 70-85% of normal snowpack. "Keep in mind that the lowest April 1 snowpack percentages since 1991 are about 50-70% of normal. One example is the Gallatin which currently has a 76% of normal snowpack. The lowest April 1 snowpack percentage since 1991 was 73% in 2001, which is not too far off from this year and also 2022," said Larson.
Ideally the mountain snowpack in Montana reaches its peak level some time from mid-April to early-May. Several lower elevation SNOTEL stations experienced melt over the last couple weeks indicating that portion of the snowpack has potentially peaked for the season. Additional accumulation in the coming months could bring a higher peak, but the given the low snow year it has been, loss of snowpack this early is not ideal. Furthermore, the snow water equivalent deficit at the highest elevations is 10-13 inches behind normal for April 1. "It is not likely those deficits will be recovered this season, and without a significant shift in weather patterns, Montanans should prepare for below normal snowmelt driven runoff this season," said Larson.
April 1 water supply forecasts currently trend with water year precipitation and the resulting snowpack. Given both are currently below normal at most locations, so are most forecasts. "In general, April through July streamflows are forecasted to be about 70-85% of normal in Montana. There are some exceptions including a couple pockets of northwest, southwest, and southern Montana. In those locations water year precipitation has been closer to normal, and as a result water supply is forecasted to be closer to normal," said Larson. Locations of greatest concern include the Teton, Shields, Nevada Creek, Bighole, Musselshell, Little Bighorn, Blackfoot, Smith, Sun, Clark Fork and Tongue River, which are forecasted to have less than 65% of normal total runoff volume during the April through July time period.
"Given the widespread lack of snow and less than ideal water supply forecasts, above normal precipitation over the next couple of months and a slow release of the snowpack is needed for the upcoming runoff season," said Larson. A wet summer could also help to sustain closer to normal streamflows later in the summer. Currently NOAA's Climate Prediction Center weather outlook indicates near normal precipitation is likely over the next 8-14 days, but there are equal chances of either below normal or above normal precipitation over the next month.
A full report of conditions on April 1 can be found in the monthly Water Supply Outlook Report available on the Montana Snow Survey website. In addition, real-time snow survey data can be found at nrcs.usda.gov/montana/snow-survey.
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