Despite spring moisture and cool temperatures in northwest Montana that helped strengthen snowpack and delay runoff this year, hydrologists expect water levels to still be below average through July after a dry winter that resulted in low snow depths in the Flathead.

The Flathead River basin is expected to experience about 80 to 90 percent of normal flow from June 1 to July, while the Sun-Teton-Marias River basin is expected to experience about 16 percent of normal flow, according to the Water Supply Outlook Report.

Eric Larson, a hydrologist with the U.S. Department of Agriculture's Natural Resource Conservation Service (NRCS), says that while the rainfall helped improve water flows in the short term, it was not enough to offset the weak snowpack.

“But it definitely helps,” Larson said. “That's the story of the last month.”

The Swan, Flathead and Whitefish mountain ranges experienced severe spring storms in May, bringing more than 30 cm of precipitation in some areas. For example, the Noisy Basin SNOTEL station in the Swan Range recorded 15 cm of snow water equivalent (SWE) and about 90 cm of snow during the first week of May. Snow depth was 132 cm on June 10.

Over the Memorial Day weekend, up to a meter of snow fell in the high elevations of Glacier National Park, followed by cool temperatures that posed major challenges for the Going-to-the-Sun Road clearing crews as they worked to clear the road.

According to snow clearing services, the snow cover in the highlands of the Glacier region was thicker than it had been in 13 years.

“Spring can be a volatile season weather-wise, and we've seen some big changes,” Larson said. “Precipitation in April, May and June is deposited on top of the snowpack and delays snowmelt.”

The Tongue and Powder River basins in southeastern Montana received the most rainfall this spring, increasing the runoff forecast through July from about 70% of normal to 130%.

SWE values ​​in the Flathead Basin are 78% of normal as of June 10, based on the median percentage between 1991 and 2020, while values ​​in the Kootenai Basin are 87% and in the Sun-Teton-Marias Basin are 0%.

Larson said all weather stations on the east side of the Continental Divide at the Rocky Mountain front have melted away, including Badger Pass, the highest elevation at 2,018 meters.

“The water supply forecast for this area is pretty bleak this year,” Larson said.

Other problem areas, according to Larson, include the Bitterroot, whose SWE level is four percent of normal, the Smith-Judith-Musselshell Basin in the central part of the state at 34 percent, and the Upper Clark Fork at 52 percent.

“Below-average snow depths this season will likely impact late-summer runoff volumes,” Larson said. “From a water supply perspective, above-average summer precipitation is almost always welcome, and slower melting of remaining snowpack at high elevations would also help maintain near-normal late-summer runoff volumes.”