Water outlook remains below average
According to the USDA Natural Resources Conservation Service (NRCS), the North Fork Jocko SNOTEL in the southern Mission Mountains has received 36.9 inches of precipitation since Oct. 1, which is the lowest May 1 water year precipitation total in 35 years of record. And that's not an anomaly.
Well-above normal precipitation during April was needed given the meager snowpack conditions experienced this year. While monthly precipitation was above normal last month in the Powder and Tongue River basins, precipitation was about 65-80% normal at basins across the state.
“A couple of mid-month storms did provide significant snowfall, but April is typically a wet month in Montana, and total precipitation last month did not meet that standard,” said Eric Larson, NRCS Water Supply Specialist.
As of May 1, the Flathead basin was at 81% average for precipitation, and 68% average for snowpack.
Although snow fell last week in the mountains, adding to the snowpack across upper elevations in Montana, it's not apt to make up for the deficit.
“It’s not uncommon to have significant snowstorms during May in Montana, particularly east of the Continental Divide,” Larson said. “While this storm is helpful, this one storm alone will not likely make up for the water year precipitation deficit across most of western Montana.”
Water year precipitation is only 75-85% of normal for most of the state. SNOTEL sites in the region extending from near Missoula to the Rocky Mountain Front and around Helena are reporting total water year precipitation that ranks in the 15th percentile or less for a 30-to-40-year period of record.
As of May 1, snowpack percentages across most of Montana range from about 55-75% of normal. The Upper Missouri near Helena and Sun-Teton-Marias are lower at about 40%. The Bighorn and Tongue River basin snowpack is closer to normal at about 80-85%.
Water supply forecasts as of May 1 align with water year precipitation and the resulting snowpack. Currently, they indicate runoff volume will be below normal this summer in most locations.
For the Flathead, Clark Fork and Blackfoot basins in western Montana, the entire range of streamflow forecasts falls below the median May-July volume for most streams. According to Larson, that means that even with well above normal precipitation during May, below normal runoff volume is expected this season.
A full report of conditions on May 1 can be found in the monthly Water Supply Outlook Report available on the Montana Snow Survey website, https://www.nrcs.usda.gov/conservation-basics/conservation-by-state/montana/montana-snow-survey/water-supply-outlook-reports-montana.