The National Weather Service reported last week that the snowpack in certain areas of the Flathead River Basin have reached historic levels, likely leading to flood or near-flood levels on the basin’s major rivers in May and June.
Ray Nickless, a hydrologist for NWS, said in a spring flooding report that some rivers, such as the Swan and the North Fork of the Flathead, are forecast to reach flood levels that could place them in the top five highest flood levels on record.
In the past three weeks, the Flathead has seen a significant increase in snowpack levels. The levels were at 141 percent of average on April 15, and recent data shows the Flathead now at 183 percent of average.
“We’re typically seeing snow water equivalents drop off pretty dramatically this time of year and we’re really not seeing that,” Nickless said.
For example, Bisson Creek in the Mission Mountains had 18.4 inches of snow water equivalent three weeks ago, which was 200 percent of the average. Currently, the site has 21 inches of snow water equivalent, Nickless said, increasing the average to 656 percent of levels for this time of year.
“This site is typically melted out this time of year,” Nickless said. “Typically it’s only got three inches of water but currently it’s got 21 inches of water.”
This area, as well as Noisy Basin in the Swan range, set new maximum records this year. Nickless also said Ashley Creek is expected to flood this spring, with flood-prone areas near Kila.
With weather forecasts calling for more precipitation in the Mission Mountains and the Bob Marshall Wilderness over May 8 and 9, and warmer temperatures expected to pick up after that, NWS officials said the snowpack could begin to soften and start melting.
Most of Western Montana is expected to flood this spring, Nickless said. In the Flathead, several major rivers could reach historic flood levels. Here’s a breakdown of some of the biggest waterways in the Flathead and their forecasted levels for the spring:
Swan River
Level on May 9: 3.71 feet
Flood Stage: 6.5 feet
Spring Forecast: 6.8 to 8 feet
Flood Potential: “It could easily make it into the top five floods on record.”
Highest Recorded Crest: 7.34 feet in 1974
North Fork – Flathead River
Level on May 9: 5.3 feet
Flood Stage: 12 feet
Spring Forecast: 12.2 to 12.8 feet
Flood Potential: Could put it in the top five floods on record.
Highest Recorded Crest: 16.9 feet in 1995
Main Stem – Flathead River
Level on May 9: 8.59 feet
Flood Stage: 14 feet
Spring Forecast: 15.5 to 16.2 feet
Flood Potential: “If we look at the Flathead rivers, we’re expecting all those to go to flood.”
Highest Recorded Crest: 25.58 feet in 1964
Middle Fork – Flathead River
Level on May 9: 4.17 feet
Flood Stage: 10 feet
Spring Forecast: 11.2 to 11.7 feet
Flood Potential: Not record levels, but still a foot above flood stage.
Highest Recorded Crest: 36.46 feet in 1964
Stillwater River
Level on May 9: 5.34 feet
Flood Stage: 7.5 feet
Spring Forecast: 7.3 to 7.7 feet
Flood Potential: “Pretty close call” whether it will make it to flood stage.
Highest Recorded Crest: None indicated
Whitefish River
Level on May 9: 4.54 feet
Flood Stage: 8.5 feet
Spring Forecast: 7 to 8 feet
Flood Potential: Expected to get close to flood stage levels.
Highest Recorded Crest: None indicated