Flood watch extended to local rivers

The National Weather Service has raised the likelihood for flooding on rivers and streams in Northwest Montana, but flooding is not expected for weeks because of continued cool weather.

Continuing precipitation in the mountains has gradually added to snowpack water content with little or no snowmelt.

Because of that, the Weather Service now forecasts flooding on most rivers and streams in the region, when just a couple of weeks ago those forecasts were limited mostly to small streams and rivers fed by lower-elevation drainages.

“We’re expecting just about every Flathead River [fork] to flood,” hydrologist Ray Nickless during a Thursday conference call with federal, state and local officials and media. “This is one of the regions that really has tremendous snowpack.”

In mid-March, higher-elevation automated snow measuring sites were recording snowpack for the Flathead River Basin at 129 percent of average. Now it’s at 141 percent of average.

The Kootenai River Basin snowpack was 121 percent of average in mid-March but now it is at 138 percent of average.

When peak runoff gets under way, Nickless forecasts the North Fork Flathead River to reach the 12-foot flood stage at Polebridge.

He predicts the Middle Fork Flathead River near West Glacier will reach 10 to 11 feet, exceeding its flood stage level of 9 feet.

The main stem Flathead River at Columbia Falls is expected to reach 14.1 to 15.8 feet, exceeding the river’s 14-foot flood stage.

The Swan River downstream from Swan Lake is expected to reach up to 6.7 feet. The Swan River has a flood stage of 6.5 feet.

The Fisher River near Libby is expected to reach 7.5 to 8.1 feet. Flood stage of 7.5  feet.

The Yaak River is expected to reach 8.2 to 8.6 feet. Flood stage of 8.5 feet.

Ashley Creek and the Little Bitterroot River still are expected to exceed flood stage and the Whitefish and Stillwater rivers are expected to approach flood stage.

Flooding still is expected on fast-reacting streams fed by runoff from the Swan and Mission mountain ranges.

All of the forecasts are based mostly on snowmelt alone. Nickless stressed that continued precipitation could elevate flows and flooding.

Below-normal temperatures and normal precipitation are expected during the next week, and as that continues the peak runoff will be delayed.

“It just depends on what happens with our temperatures going into the end of May. We may not see any flooding until June,” Nickless said. “I think this year we’ll probably see flooding in May and June.”

Nickless was asked if an incremental, intermittent runoff would make a difference.

“That would certainly help if we go into the snowmelt period with no big rain events,” he said.

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