More snow needed to improve summer’s water outlook

While February moisture boosted snowpack levels across the state, March didn’t help much – except in southwest and southern parts of the state.

However, recent rains have boosted precipitation in the Flathead basin, dumping 153% of 1991-2020 average precipitation for the first week of April. The upper and lower Clark Fork basins also received significant boosts.

Still, the overall outlook for March wasn’t helpful in western Montana according to the Natural Resources Conservation Service's monthly water-supply outlook, released April 5.

“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 NRCS Water Supply Specialist Eric Larson.

What seemed to promise the beginning of a potential recovery then tapered off in many basins.

Precipitation in the Flathead basin remained below normal as of April 1 at 71%, which brings the seasonal accumulation (October-March) to 80% of median. The snowpack in the Flathead is also well-below normal at 75% of median, compared to 92% at this time last year.

March precipitation in the Kootenai basin was near normal at 96%, which brings the seasonal accumulation (October-March) to 88% of median. The snowpack in the Kootenai remains well-below normal at 78% of median, compared to 85% at this time last year.

The Upper Clark Fork basin is also sparse: precipitation in March was well-below normal at 75%, which brings the seasonal accumulation (October-March) to 71% of median. This brings the basin to even further below normal at 67% of median, compared to 114% at this time last year.

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 given the low snow year it has been, loss of snowpack this early is not ideal, said Larson. 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,” he added.

In its initial water-supply forecast, the NRCS suggests April-through-July streamflows will be about 70-85% of normal in Montana.

“There are some exceptions – including a couple pockets of northwest, southwest and southern Montana,” Larson said. In those locations water-year precipitation has been closer to normal, and as a result water supply is forecasted to be closer to normal.

“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.