Wyoming Water Supply Outlook--Last Update for 2010 Water Year

 …Mountain snowpack above the 9500 foot elevation continues to be well above normal--across central and eastern Wyoming…

...Well above normal summer runoff volumes area expected across all basins east of the continental divide---Below normal summer snowmelt runoff volumes are expected across the rest of Wyoming's major basins...

…Seminoe and Pathfinder Reservoirs are 100% full.  Reservoir storages statewide remain at 100 to 125 percent of average…

An extreme rapid snowmelt event followed by an extraordinary rainfall event during the second week of June caused extreme excessive runoff along rivers east of the continental divide.  Record breaking flows in several rivers in central and southeastern Wyoming quickly filled many reservoirs across the region. Seminoe and Pathfinder Reservoirs filled to capacity by June 15th.  The Snake River Basin and the upper portions of the Shoshone Watershed also experienced a moderate to heavy rain event in early June. 

The extraordinary “rain on a melting snow” event caused rapid snowmelt of the 8500 to 9500 foot elevation snowpack.  Mountian snowpack numbers before the event (as of June 1) were generally well above normal at 110 to 125 percent of normal. Snowpack "water" numbers and/or snow water equivalent (SWEs) figures at the beginning of June continued to be the highest across southeastern Wyoming--with 110 to 121 percent of normal.  SWE averages across the rest of Wyoming varied from 67 to 100 percent of normal.

Current (as of June 18th) mountain snowpack numbers at elevations above 9500 feet across central and eastern Wyoming continue to well above normal--varying between 90 and 200 percent of normal.

All major watersheds east of the continental divide will continue to see well above normal summer runoff values.  The Snake, Upper Yellowstone, and Upper Green River Basins will are still expected to see well below average summer snowmelt streamflow volumes.

The latest Wyoming water supply outlook graphic:


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