PROJECT ALERT NOTICE (MT WY) Severe to extreme drought continues in Wyoming

Date: Wed, 19 Aug 2020 11:54:10 EDT

Summary: More than one third of Wyoming is experiencing severe to extreme drought conditions during August.

The National Drought Monitor (https://droughtmonitor.unl.edu/) classified about 35 percent of Wyoming as experiencing severe to extreme drought conditions for the month of August to date. Current seven-day average streamflows at more than 50 USGS streamgages in Wyoming and Montana with 30 or more years of data are below normal for August 18 (reference map linked below).

Seven-day average streamflows at selected USGS streamgages in Wyoming and Montana with minor to no anthropogenic influences (reference table linked below) are categorized as moderate to severe hydrologic drought. The 7-day averages through August 18 range from the 10th to the first percentiles derived from periods of record that range from 36 to 107 years.

Two USGS streamgages on the upper North Platte River in Wyoming indicate moderate to severe hydrologic drought. Streamflow percentiles (9th and 3rd) at the sites are based on 81 to 106 years of record respectively and partially influenced by upstream diversions. Severe to extreme hydrologic drought observed at some USGS streamgages in Montana are partially to entirely a function of altered streamflows resulting from construction projects.

USGS field staff continue to complete discharge measurements to validate stage-discharge relations and determine shifts as appropriate. To date, no special measurements have been needed to supplement routine activities. At sites recording below normal streamflows, one (USGS 06620000) required the orifice to be lowered to ensure complete gage-height record as river stages continue to decline.

USGS staff contribute weekly to the Montana recommendations for National Drought Monitor by assisting with interpretation of USGS streamflow data. USGS staff have offered the same service to Wyoming.

Moderated to severe drought observed at streamgages not affected by diversions, Wyoming and Montana
Map of below normal 7-day average streamflow compared to historical streamflow for the day of the year, Wyoming and Montana