Flooding and High-Flow Conditions in Wyoming and Montana

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By Wyoming-Montana Water Science Center March 26, 2018

Greybull River near Basin, Wyoming

June 1963

N F Flathead River at Blankenship Bridge near Columbia Falls, MT

1964

Swiftcurrent Creek at Many Glacier, MT

Nov. 7, 2006 @ 1400 hrs

Wind River near Crowheart, WY

June 15, 2017 @ 13,300 ft3/s

The USGS monitors flood and high-flow conditions at more than 300 streamgages across Montana and Wyoming. Water level and flow information are used by the National Weather Service (NWS) to make accurate flood forecasts. High-flow conditions are expressed as percentiles comparing current (within the past few hours) instantaneous flow to historical daily mean flow for all days of the year.

A percentile is a value on a scale of one hundred that indicates the percent of a distribution that is equal to or below it.

"<95" indicates that the estimated streamflow is less than the 95th percentile for all days of the year,
"95-98" indicates that the estimated streamflow is between the 95th and 98th percentiles for all days of the year,
">=99" indicates that estimated streamflow is greater than the 99th percentile, and
"Not ranked" indicates that a flow category has not been computed. Common reasons for a "Not ranked" category are insufficient historical data or no current streamflow estimates.

Flood stages are determined by the NWS; not all USGS streamgages have flood stages. A depiction of other streamgages at or above flood stage is available the NWS River Conditions Map.

Current Flooding and High-Flow Conditions:
(Current-conditions data are provisional and subject to change)

Wyoming:

Map: Flood and high flows
Data table: Locations above flood stages
Map: Current streamflow conditions vs historical streamflows
Flood of August 1, 1985 in Cheyenne, WY
Floods of May 1978 in southeastern Montana and northeastern Wyoming

Montana:

Map: Flood and high flows
Data table: Locations above flood stages
Map: Current streamflow conditions vs historical streamflows
Floods of May 1981 in west-central Montana
Floods of May 1978 in southeastern Montana and northeastern Wyoming
Floods of June 1964 in northwestern Montana

Sources/Usage: Public Domain. View Media Details

Devastating floods across much of the U.S. were severe and unrelenting during the spring and summer of 2011. When floods happen, USGS crews are among the first-responders. Often working in dangerous conditions, USGS scientists measure streamflow and river levels, repair and install streamgages, measure water quality and changes in sediment flow, and assess river changes. From flood forecasts to difficult decisions about flood management, science is critical for flood preparations and response.

How can a 100-year flood strike twice in 15 years? This is a downloadable poster discussing the meaning and use of probability language in flood characterization.
Poster: 100-Year Flood--It's All About Chance

Below are publications associated with floods and high-flows in Wyoming and Montana.