First a heat wave, then high water

Record temperatures expected to drive flooding by Monday

Record high temperatures over the weekend are expected to drive flooding by Monday on Western Montana rivers and streams, including rivers in Flathead and Lincoln counties.

More than 30 local emergency responders met in Kalispell on Thursday for a teleconference update from the National Weather Service in Missoula.

"We certainly have a pretty big high-impact weather event coming our way," said meteorologist Bruce Bauck. "This is truly a very exceptional heat wave for this time of year."

High temperatures are expected to be in the upper 80s in Kalispell and in the 90s in Missoula through Monday.

But more importantly, Bauck said, snowpack melting will not be slowed overnight, when high-elevation temperatures will drop only into the 50s.

The heat wave will be followed by a rapid cooling with potential for rain starting Tuesday.

"We should go from these record high temperatures to temperatures below normal by Tuesday" with rain, Bauck said. "The big question is how much precipitation will come."

Ray Nickless, a hydrologist with the service, said the runoff should be rapid.

Thursday's streamflow forecast models are projecting several rivers in Northwest Montana to approach or exceed flood stage by Monday afternoon:

. The Yaak River at Troy is expected to reach 8.21 feet, just above its 8-foot flood stage;

. The Fisher River near Libby is expected to reach almost 8.5 feet, 1 foot above its 7.5-foot flood stage;

. The North Fork Flathead River is expected to reach its 12-foot flood stage at Polebridge;

. The Middle Fork Flathead River is expected to reach a 10.5-foot flood stage at Essex;

. The Middle Fork Flathead River is expected to top 11 feet, exceeding its 10-foot flood stage at West Glacier;

. The main Flathead River at Columbia Falls is expected to reach nearly 16 feet, exceeding its 14-foot flood stage by two feet.

That raises the potential for flooding at locations along the Flathead River below Columbia Falls.

The Flathead County Office of Emergency Services has identified a series of areas that are prone to flooding, including Polebridge, Mosquito Flats in Columbia Falls, lower Trumble Creek, Star Meadow, Kokanee Bend south of Columbia Falls, east Evergreen, Leisure Island south of Kalispell and lower valley farmlands.

The weather service's forecasts have been adjusted daily for the past week, and that will continue through the weekend.

"We will make adjustments over time as we see how this snowpack is melting," said Nickless, who noted that actual flows could be above or below current forecasts.

Nickless said the heat wave will melt a substantial amount of the snowpack, which is at 133 percent of average in the Flathead Basin and 148 percent of average in the Kootenai Basin. But lingering snow, the potential for rain, and rivers flowing high will combine for a prolonged flood risk.

"There certainly is a potential for a dual peak," he said. "We could see this rise this weekend and into next week, and then we get another bunch of melting with rain on top of it and we could get another peak."

And Nickless noted that there is potential for small-stream flooding issues.

Potential flooding is expected on streams flowing from the 30,000-acre area burned by last summer's Brush Creek Fire west of Whitefish.

"Certainly the flooding potential is higher because of the burned landscape," said Craig Kendall, hydrologist on the Flathead National Forest. But that risk may be offset because of extremely dry soils and because much of the lower elevation areas in the burn have already melted off.

"There are culverts in that area that we are concerned about," Kendall said.

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