Forecasters expect spring flooding

Based on a recent survey of low-elevation snow, a hydrologist with the National Weather Service in Missoula anticipates small-stream flooding and possibly river flooding in Northwest Montana.

“Our main mission was to get a better handle on the low-elevation snow depths and snow-water equivalents,” hydrologist Ray Nickless said.

The Natural Resources Conservation Service is able to closely monitor mountain snowpack with the use dozens of automated snow measuring devices. But there isn’t a similar network for measuring snow accumulations at lower elevations.

Because significant snow remains in lower areas as of mid-March, Nickless surveyed areas in Lake, Flathead, Lincoln and Sanders counties Wednesday and Thursday.

On the lower slopes of the Mission Mountains in Lake County, snow has mostly melted out, he said, but the snowpack at high elevations is well above average.

An automated site at 4,900 feet in the Bisson Creek drainage, for example, shows a snow-water equivalent of 16.7 inches, the highest at this time of year since the big winter of 1997.

“We’re looking at small creeks in the Missions to flood,” he said, noting that there was flooding on Mission Mountain creeks in 1997.

In Flathead and Lincoln counties, Nickless found ample snow at lower elevations.

“To the west of Kalispell, snow that drains into Ashley Creek, the Thompson River, the Fisher River, the Little Bitterroot River ... we found that they still have plenty of water,” Nickless said.

A site at 4,000 feet that feeds into the Ashley Creek drainage had 19 inches of snow with 4.5 inches of water. A site above the Little Bitterroot drainage had 22 inches of snow on the ground with 5.7 inches of water. A site above the Thompson River drainage had just 13 inches of snow but a snow-water equivalent of 4.1 inches.

One of the few automated sites in the mountains west of Kalispell — at Hand Creek on the Flathead-Lincoln county boundary — is measuring a snowpack at 130 percent of average with a whopping snow-water equivalent of 14.3 inches.

Those measurements and others lead Nickless to expect ample low-elevation runoff once a period of sustained warm weather sets in. The various drainages west of Kalispell are mostly impacted by low-elevation runoff, and the Fisher River in particular is prone to flooding.

“Right now our concern that we’ll see flooding on those rivers and creeks in that area when we get into a heavy melting period,” Nickless said.

 But flooding may not be limited to areas Nickless was able to survey.

Low-elevation runoff typically influences other flood-prone drainages such as the Stillwater River and Trumbull Creek. Last spring, Trumbull Creek flooded near U.S. 2 west of Columbia Falls.

Flooding driven by high-elevation snowpack typically happens later in the spring and it depends on how the runoff develops. Cold nights, for example, can lead to a tempered, gradual runoff without flooding.

Mountain snowpack above the Flathead River Basin is 130 percent of average and above the Kootenai Basin it is 124 percent of average.

“We’re going to see high water across most of the Flathead drainage, including the Flathead River,” Nickless said. “Whether the Flathead River itself reaches flood stage will depend on how the runoff plays out.”

Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com.