The National Weather Service says the Flathead River has a 95 percent chance of flooding in May or June, and an incoming rainstorm this weekend isn’t going to help.
Ray Nickless, a hydrologist with the NWS in Missoula, held a flood potential webinar on April 26 that showed snowpack still at 167 percent of normal in the Flathead basin. The Flathead River, measured at Columbia Falls, has the second-highest chance of flooding among the Western Montana rivers shown in Nickless’ presentation, trailing only the Clark Fork near Missoula at 97 percent.
“It’s almost certain to exceed flood stage,” Nickless said of the Flathead River. “It’s just a question of how high it will get.”
A rainstorm is expected to arrive in Western Montana Saturday and linger into Monday, hitting Northwest Montana hardest, although Nickless said the storm has been changing daily as it moves inland from the coast, making it hard to measure its severity.
As of April 26, Marias Pass was expected to receive the most precipitation over the weekend with 1.95 inches. More than an inch was forecast in other parts of the region, including 1.12 in Kalispell.
“These forecasts could certainly change as we get into tomorrow,” Nickless said.
In any case, the rain will have an impact. At higher elevations, Nickless said it could be absorbed into the snowpack or in fact become snow.
“The rain this weekend isn’t going to help,” Nickless said. “It’s just going to prime these rivers.”
Following the rain, cooler temperatures will provide a brief reprieve before heating up again later in the week and raising river levels with snow melt-off from the mountains. Nickless showed graphs of the Yaak and Fisher rivers in Lincoln County, which are at lower elevations, rising significantly in the coming days.
“This is really just the primer, the start of it,” Nickless said of the upcoming rainstorm’s impact on high-water season, which peaks in May or June. “We’re not expecting a lot of large flooding from it, (but we’ll) see some things start to rise up.”
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