BOZEMAN – Following two months of well below average precipitation, rain and snow was welcomed across much of Montana during May. Two mid-month storms brought significant precipitation to the Rocky Mountain Front and portions of the Flathead River Basin according to data from the USDA’s Natural Resources Conservation Service (NRCS). SNOTEL sites near Seeley Lake and Lincoln, Mont., received record amounts of May precipitation. Overall, the recent precipitation was beneficial and added much needed snow to the remaining upper elevation snowpack across the region. Unfortunately, other portions of Montana received well below average precipitation including portions of the Clark Fork river basin, northeastern Beartooths, and Central Montana from Wyoming’s Bighorns north to Glasgow. The good news is according to the National Weather Service, “This ranked as the 15th wettest May on record for Montana, and the wettest since 2018.”
Water users across Montana have seen stream levels rise over the last month, and a substantial portion of this year’s snowpack has melted as of June 1. “The snowpack in the state peaked early and at below average levels in most locations,” said Mage Hultstrand, Acting NRCS Montana Water Supply Specialist. A couple locations did peak above average such as the Upper Clark Fork, Upper Bitterroot, and Bighorns, which will result in sustained streamflow this summer. Mid-to-low elevation snowpack melted out weeks ago, slightly ahead of schedule. These melt-outs can be attributed to warm temperatures in April that caused above average melt rates. May weather patterns were more favorable to slowing snow melt rates. However, the first week of June brought the hottest temperatures of the year and rapid melt of all high elevation snow. This rapid melt drove many rivers to their annual snowmelt peak.
As the remaining snowpack melts in the coming months, streams will run out of snow water and begin their decline into summer. June 1 streamflow forecasts vary widely across the state. While May precipitation increased forecasted streamflow volumes for much of the Flathead and Rocky Mountain Front Range river basins, many southwest Montana river basins remained below average or even declined. “The Jefferson and Madison river basins, which have been a concern for most of the season, did receive good precipitation from the storms in May but it was not enough to make up for water year deficits from the lack of precipitation in March and April,” said Hultstrand. On the upside, streamflow forecasts for some of the larger basins such as the Gallatin and Yellowstone River basins are near normal.
According to NOAA’s Climate Prediction Center, the next several weeks have the potential for warmer than normal temperatures and, according to the 8-14 day and 30-day models, below normal precipitation. The long-range forecast also calls for a continuation of conditions seen throughout much of this year: increased chances of warmer and drier weather than normal. Current water year precipitation (October 1, 2020, to current) is near to below average in most locations.
A full report of conditions for June 1 can be found in the monthly Water Supply Outlook Report available on the Montana Snow Survey website on Monday, June 7. In addition, real-time snow survey data can be found at https://www.nrcs.usda.gov/wps/portal/nrcs/mt/snow/.