Water Supply Outlook Reports - Montana

Warm temperatures and lack of precipitation over the last couple months have resulted in a bleak start to the seasonal snowpack in Montana and northern Wyoming. Precipitation since October 1 has mostly been well below normal. As a result, the snowpack is currently about 30-60% of what it normally is this time of the year, except for part of the southern Absaroka and Wind River Mountains. Currently many NRCS snow monitoring stations in the region are reporting their lowest snowpack on record. Additionally, temperatures have been significantly warmer than normal during the last two months, as a result the snowpack has experienced some melt.

An early January storm brought hope that normal winter weather had finally arrived. After record setting cold temperatures settled in mid-month for about a week, well above normal temperatures accompanied by dry weather returned and persisted during the last two weeks of January in all but the northern Flathead and Kootenai River basins.
Most basin wide snowpack percentages haven’t changed much since January 1, and are still well below normal. Above normal precipitation was needed to make significant gains on the snowpack deficit, yet January precipitation was below normal in all but the Kootenai River basin. Currently, all snowpack percentages are below normal.

Following an exceptionally slow start to the water year, winter weather arrived in February and provided much needed precipitation to the region. Precipitation last month was above normal in all but the northern Bighorn Mountains. Snowpack percentages have increased in all basins, but overall, the snowpack remains below normal. The recent improvements were timely, but there are only one to two months remaining in the normal snow accumulation season and more snow is needed.

Given the lack of precipitation from November through much of January in Montana, above normal precipitation was needed over the last couple of months to begin to catchup on snowpack and precipitation. February provided well above normal precipitation to nearly all of Montana. Basins such as the Jefferson and Upper Missouri received over 150% of normal precipitation during February and those weather patterns continued into the first week of March across much of Montana. What seemed to be the beginning of a potential recovery tapered off after the first week of March in many basins. Overall precipitation was above normal in southwest and southern Montana, but mostly below normal elsewhere.

Well above normal precipitation during April was needed given the meager snowpack conditions experienced this year. Total monthly precipitation was above normal last month in the Powder and Tongue River basins, but was not widespread across Montana. A couple 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. April precipitation was overall about 65-80% of normal with a couple of isolated locations that were higher. For example, the Gallatin and Bitterroot received about 90-95% of normal April precipitation. Spring weather in Montana can be highly variable, with a storm that is currently adding to the snowpack as this report is being prepared. While this is exactly what is needed, this one storm alone will not likely make up for the water year precipitation deficit across most of western Montana. Water year precipitation is 75-85% of normal for most of the state. Northern Wyoming basins and the upper Madison have fared slightly better and are currently at 90-100% of normal water year precipitation.

Snow Surveyors Elena Garcia and Zachary Denison measuring Norris Basin Snow Course in Yellowstone National Park on January 1, 2023. They found 4.4” of snow water equivalent at the snow course, which is above normal for January 1 and similar to conditions across the rest of the region. The snowpack is off to a good start this year and across Montana conditions are currently above normal. The timing of snowpack onset this season was near normal, and precipitation has been consistent since October, however there are still 3 to 4 months left in the snowpack accumulation season. Continued active weather in the months ahead will be necessary to reach normal spring snowpack levels.

Although much of January consisted of sunny days without precipitation, a major winter storm during the last week of the month added to the snowpack while also improving snow conditions for recreationalists. This storm provided some locations in Montana with two to three feet of snow. While this storm was beneficial, most snowpack percentages decreased over the last month. The snowpack currently ranges from below normal in northwestern Montana and the Rocky Mountain Front to above normal in central Montana. With two to three months remaining in the typical snowpack accumulation season, some uncertainty remains in terms of what spring snowmelt will provide for water supply.

Photo of the northern Bridger Range on February 24 when the ridge top wind gusted 40-50 mph as the weather transitioned from cold and snowy to warm and sunny. Similar to January, February ended with a large storm that brought several feet of mountain snow across much of Montana. February however had more consistent precipitation than January and snowpack percentages are currently near to well above normal in most river basins. Exceptions are basins along the far western and northwestern border of Montana, where the snowpack is below normal. With one to two months remaining in the typical snowpack accumulation season, water supply forecasts are now available statewide.

Photo of Montana Snow Survey Hydrologist Colin Kultys surveying Slag-A-Melt Lake Snow Course in the Beaverhead Mountains on March 28, 2023, a region that experienced active weather in March and rebounded from below normal conditions last month. Excluding Northwest Montana and the Rocky Mountain Front, March precipitation was above normal in Montana. Central Montana and Southwest Montana continued to build on an already exceptional snowpack. Peak snowpack season is upon us and much of the snowpack east of the Continental Divide is near or already exceeding normal peak levels. Snowpack conditions across the state are largely above normal, except in the far northwest region of Montana. April 1 streamflow forecasts are now available in the following report.

Warm temperatures during the week of April 10th resulted in significant melt of snowpack below mid-mountain elevations across Montana. The photo above shows the Shields River near Livingston exceeding its banks on April 12th when it reached an estimated peak streamflow of nearly 5000 cfs, which was the second highest peak on record, only behind 1979. The snowpack across all of Montana appears to have peaked for the season. Low elevation mountain snowpack has seen significant melt and many snow survey stations below 6000 ft have melted out. The high elevation mountain snowpack has only begun to melt. While it’s starting to feel like summer, it’s not uncommon to get rain and snow in May in Montana and snowpack conditions could still change. May 1st USDA-NRCS seasonal water supply forecasts are now available in the following report.

Faster than normal snowmelt during May resulted in a decrease in snowpack percentages from last month and the seasonal snowpack at many monitoring stations melted out earlier than normal. The snowpack only remains at the highest elevations across Montana. While much of the seasonal snow has melted, the total volume of snow water equivalent accumulated this year was near to above normal in all but part of northwest Montana and the northern Rocky Mountain Front. Last month’s rapid snowmelt resulted in reduced water supply forecasts for the summer at most stream gages. Given the quick melt, a normal amount of precipitation over the next several months will be necessary to sustain normal streamflows late into the summer.