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
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 other science projects associated with floods and high-flows in Wyoming and Montana.
Black Hills Area Floods - 1921 to 1930
Black Hills Area Floods - 1961 to 1970
Black Hills Area Floods - 1931 to 1940
Black Hills Area Floods - 1901 to 1910
Black Hills Area Floods - 1941 to 1950
Black Hills Area Floods - 1951 to 1960
Black Hills Area Floods - 1911 to 1920
Black Hills Area Floods - 1971 to 1980
Black Hills Area Floods - 1877 to 1890
Black Hills Area Floods - 1891 to 1900
The 1972 Black Hills-Rapid City Flood
Below are news stories associated with floods and high-flows in Wyoming and Montana.
Study Links Major Floods in North America and Europe to Multi-Decade Ocean Patterns
The number of major floods in natural rivers across Europe and North America has not increased overall during the past 80 years, a recent study has concluded. Instead researchers found that the occurrence of major flooding in North America and Europe often varies with North Atlantic Ocean temperature patterns.
- Overview
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.
Sources/Usage: Public Domain. Visit Media to see details.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
Sources/Usage: Public Domain. Visit Media to see details.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
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 - Science
Below are other science projects associated with floods and high-flows in Wyoming and Montana.
Black Hills Area Floods - 1921 to 1930
Black Hills Area Floods - 1921 to 1930Black Hills Area Floods - 1961 to 1970
Black Hills Area Floods - 1961 to 1970Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1931 to 1940
Black Hills Area Floods - 1931 to 1940Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1901 to 1910
Black Hills Area Floods - 1901 to 1910Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1941 to 1950
Black Hills Area Floods - 1941 to 1950Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1951 to 1960
Black Hills Area Floods - 1951 to 1960Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1911 to 1920
Black Hills Area Floods - 1911 to 1920Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1971 to 1980
Black Hills Area Floods - 1971 to 1980Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1877 to 1890
Black Hills Area Floods - 1877 to 1890Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.Black Hills Area Floods - 1891 to 1900
Black Hills Area Floods - 1891 to 1900Look under the Multimedia table for pictures and more information regarding the event date and location, flow data (if available), a brief summary of the event, and links to available photographs or scanned newspaper articles.The 1972 Black Hills-Rapid City Flood
The 1972 Black Hills-Rapid City Flood Revisited - Data
- Publications
- Web Tools
- News
Below are news stories associated with floods and high-flows in Wyoming and Montana.
Study Links Major Floods in North America and Europe to Multi-Decade Ocean Patterns
The number of major floods in natural rivers across Europe and North America has not increased overall during the past 80 years, a recent study has concluded. Instead researchers found that the occurrence of major flooding in North America and Europe often varies with North Atlantic Ocean temperature patterns.