Local flooding threat grows: 'It's going to be hard to avoid'

Snowpack keeps growing, as does flood threat

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As the big chill continues, the snowpack across Western Montana and particularly in the Flathead River Basin persists along with continued forecasts for high flood potential.

In a Thursday briefing, the National Weather Service in Missoula maintained and in some cases upgraded its high-water forecasts for Northwest Montana rivers and streams.

Hydrologist Ray Nickless emphasized that the problem is that there has been little snowmelt in a snowpack that has actually gotten deeper in some areas through the month of April.

“The rate of melt that occurs this time of year on average is much higher,” he said.

In Northwest Montana, he said, “we’ve got so much snow here that it’s going to be hard to avoid flooding.”

The overall Flathead Basin snowpack is at 167 percent of average. However, some of the higher elevation automated snow monitoring sites far exceed that average.

The Bisson Creek site in the Mission Mountains is at 433 percent of average; the Emery Creek site above Hungry Horse Reservoir is at 240 percent of average; the Grave Creek site is at 300 percent of average; and the Many Glacier site is at 300 percent of average.

While the Noisy Basin site on the Swan Range is at 167 percent of average, snow depths there hold 72 inches of water, far above the average of 49.9 inches.

Nickless predicts streams flowing out of the Swan and Mission mountains will flood. And in the valley floor below those streams, “we’ll see a lot of groundwater popping up, sort of mini-lakes that will be popping up in the valley.”

But none of it will happen until the runoff gets under way, and the National Weather Service still is not expecting that to happen until later in May.

“Once we go into this flooding, I see it persisting into June,” said Nickless, who stressed that river forecasts could be exceeded in the event of significant rainfall or extended periods of warm weather.

Here’s a rundown on current flood forecasts for the region’s rivers:

• The Swan River downstream from Swan Lake is expected to reach 6.5 to 7 feet. Flood stage is 6.5 feet.

• The North Fork Flathead River at Polebridge is expected to reach 12 to 12.5 feet, with flood stage at 12 feet.

• The Middle Fork Flathead River is expected to reach 10.1 to 11.3 feet with flood stage at 10 feet.

• The main Flathead River at Columbia Falls is expected to reach 14 to 16 feet with flood stage at 14 feet.

• The Stillwater River is expected to reach 7.3 to 7.7 feet. Flood stage is 7.5 feet.

• The Whitefish River is expected to reach 7 to 8 feet, with flood stage at 8.5 feet.

• The Thompson River is expected to reach 7 to 8 feet, with flood stage at 7 feet.

• The Fisher River is expected to reach 7.5 to 8 feet, with flood stage at 7.5 feet.

• The Yaak River is expected to reach 9 to 9.7 feet. Flathead stage is 8 feet.

Meanwhile, a winter weather advisory was in effect for today along the Continental Divide for the Glacier National Park area. Snow accumulations of 6 to 10 inches are forecast for higher elevations and 2 to 4 inches at lower elevations.

Areas expected to be impacted include Marias Pass, Bad Rock Canyon, Essex and Montana 83 from Bigfork to Swan Lake.

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

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