Water Resources of the United States

PROJECT ALERT NOTICE (MT) Minor to major flooding is occurring in western Montana

Date: Thu, 10 May 2018 14:40:59 EDT

Summary: Minor to major flooding is occurring in the Clark Fork River basin in western Montana.

Minor to major flooding is occurring in the Clark Fork River basin in western Montana. Melting of low- to mid-elevation mountain snowpack in combination with rainfall in some areas has resulted in streamflows exceeding National Weather Service minor to major flood stages at 7 USGS streamgages in the basin. The most significant flooding is occurring in and near Missoula, Montana.

Streamflows are expected to peak later this week and into next week. Forecasted peaks could have annual exceedance probabilities ranging from less than 10 percent to greater than 4 percent. Forecasted peaks could be the largest since 1953. Daily streamflow records at several USGS streamgages are longer than 80 years. Mandatory evacuations for about 60 homes have been issued to residents in and near Missoula, Montana.

Two teams of two hydrographers and one individual are deployed making discharge measurements in the Clark Fork River and Flathead River basins. A stage sensor was relocated at one streamgage to address data-quality concerns.

Discharge measurements and any resets, shifts, and instrumentation status updates are posted to NWSChat. Current photographs from the field are highlighted on the Center's home page "carousel" and Center social media accounts are being used extensively to post streamflow data and distribute site photographs. NBC Montana interviewed staff in the office and field. Links to those stories and newscasts were provided in the Center's contribution to the Weekly Highlights and are available on request.

Map of flood and high-flow conditions, Missoula, Montana

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