Wyoming Drought Information and Graphics--updated June 17, 2008

…May precipitation across Wyoming’s river basins averaged 92 to 255 percent of average…  

…May and early June precipitation brought Riverton and Lander to greater than 120 percent of normal precipitation for the calendar year…

…Wyoming snowpack 149 percent of average as of June 11th…  

…Seminoe Reservoir already half full--Boysen Reservoir nearly three-quarters full….

…Severe hydrologic drought conditions continue over the Upper and Lower Green River Basins…  


May rainfall across Wyoming’s river basins averaged 95 to 255 percent of average.  More importantly, the lower elevations to include range lands, pasture lands, and other agricultural centers across Wyoming received a soaking rain during May and early June.  Riverton and Lander, before the May and early June precipitation, had only 54 and 43 percent of the normal yearly totals, respectively. After the rainfall in May and early June, Riverton’s yearly total has increased to 133 percent of normal; while Lander’s precipitation totals increased the yearly total to 124 percent of normal. Basin-wide precipitation totals across Wyoming for the water year 2008 (October07 - May 08) are 90 to 140 percent of normal.  The long-range precipitation forecast (July through September) is calling for near normal precipitation across central and eastern Wyoming; with below normal precipitation expected over western Wyoming.  

Water (or snow water equivalents--SWEs) in the Wyoming snowpack continued to be near normal to above normal during May--to right into the middle of June. Snowpack averages across Wyoming were still near normal (149% of the 30-yr normal) as late as June 11th.      One year ago the SWE averages across Wyoming were only 16% of normal.

Wyoming’s water supply still looks like it will be solid for the rest of the runoff and into the middle of summer. The latest water supply forecast indicates the most of the state will see normal to above normal streamflow volumes during the early to middle summer runoff.  May inflows into Seminoe, Guernsey, and Glendo Reservoirs were well above average. Summer inflows to almost all of the major reservoirs are expected to be near normal to slightly above normal. Seminoe Reservoir is over half full (54% capacity as of June 16th).  The last time that Seminoe Reservoir was at least half full was in 1999.  USBR officials expect the reservoir to remain around 60 percent full for the rest of the water year. Boysen Reservoir is nearly three-quarters full (as of June 16th) and is expected to fill by late June/early July.  Boysen Reservoir nearly filled in June of 2005.  The long-range temperature outlook still indicates that there is a 30-40 percent chance of a warmer than normal summer for most of central and western Wyoming.  This may initially help with increased inflows into most of the state’s reservoirs; but a warmer than average summer may not carry the state’s irrigation water supply deep into summer and into early fall.  

The Upper and Lower green River basins continue to under severe hydrologic conditions.  The latest drought outlook through August 2008 indicates that most of Wyoming will see continued improvement in the current hydrologic drought.

For the rest of the Wyoming Drought Information Statement and Graphics (in .PDF format)---please go to:


For additional drought graphics and information---please refer to:


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