Wyoming Water Supply Outlook Report
May 1997

General
Water conditions across Wyoming are very good. April precipitation varied from slightly above normal to much above normal. Snowpack in all the basins is above average for this time of year. Nearly half of the State is approaching maximum snow water equivalent levels for the year. Precipitation for the year is good across the State with all areas above average. Reservoir storage is looking very good across the State also. There should be no water shortages this year, if the current trend continues.

Snowpack
Snowpack over the State is above normal to much above normal for this time of the year. In some portions of the state, especially the north and west, SWE is well ahead of last year at this time. Some basins remain at record levels, especially the Snake, Madison, Shoshone, and Yellowstone River basins. The Powder-Tongue River drainage currently has the lowest percentage of average SWE (117 percent). Madison and Yellowstone River drainage SWE is about 168 percent of normal, followed closely by the Snake River drainage at about 158 percent of average. Six of the thirteen major river basins' SWE is more than 145 percent of average.

Precipitation
Many basins in the state received near average and above precipitation during the month. The Powder and Tongue River basin has received the lowest precipitation in the state so far this water year (Oct - Sep). The entire State has above normal year-to-date precipitation. The extremes are Powder - Tongue (12% above average) and the Yellowstone and Madison Basin (58% above normal). 

Basin                     Departure       Basin                      Departure
                          from normal                                from normal
Snake River               +36%            Upper North Platte River   +23%
Yellowstone & Madison     +58%            Lower North Platte         +22%
Wind River                +29%            Little Snake River         +15%
Big Horn                  +14%            Upper Green River          +21%
Shoshone & Clarks Fork    +53%            Lower Green River          +31%
Powder & Tongue River     +12%            Upper Bear River           +41%
Belle Fourche & Cheyenne  +55%
Streams
April precipitation was generally above average. All basins in the state should see average or above average runoff -- in some cases there will be much above average yield. Record SWE is being recorded in some portions of the state (generally the northern and western portion); high runoff might be expected in those portions of Wyoming. Under the right conditions exceptionally high flows could occur in the areas with record snow levels. Water users should not expect any shortages during the irrigation season.

Reservoirs
Reservoir storage varies from well below to well above average. Generally speaking, reservoir storage in the portions of the State that expect large amounts of runoff has been lowered to below average volumes. Most reservoirs should fill to capacity this year. Many reservoirs were lowered significantly this last month in anticipation of excessive flows during the runoff season. See following table for further information about reservoir storage.

Major Reservoirs in Wyoming

                               B A S I N    W I D E
                      R E S E R V O I R    S U M M A R Y

                        FOR THE END OF  APRIL   1997


 BASIN AREA         CURRENT AS  LAST YR AS  AVERAGE AS  CURRENT AS  CURRENT AS
  RESERVOIR         % CAPACITY  % CAPACITY  % CAPACITY   % AVERAGE   % LAST YR
------------------------------------------------------------------------------
  ALCOVA                    98          98          98         100         100
  ANGOSTURA                 99          99          93         106         100
  BELLE FOURCHE            100         101          82         122          99
  BIG SANDY                 81          86          62         129          94
  BIGHORN LAKE              52          57          58          89          91
  BOYSEN                    64          76          84          76          84
  BUFFALO BILL              46          57          52          88          79
  BULL LAKE                 53          64          53         101          83
  DEERFIELD                 97          99          89         108          98
  EDEN                      61          55          50         122         111
  ENNIS LAKE                80          71          86          93         112
  FONTENELLE                39          33          47          83         120
  GLENDO                    96          97          90         107          99
  GRASSY LAKE               90          90          77         117         100
  GUERNSEY                  68          69          72          95          98
  HEBGEN LAKE               63          72          65          97          88
  JACKSON LAKE              51          63          54          95          81
  KEYHOLE                   96          77          57         170         125
  PACTOLA                  101         100          87         116         101
  PALISADES                 19          29          68          27          64
  PATHFINDER                91          91          60         151          99
  PILOT BUTTE               75          79          95          79          96
  SEMINOE                   60          62          39         156          97
  SHADEHILL                 95          78          80         119         122
  TONGUE RIVER              26          40          54          49          66
  VIVA NAUGHTON RES         28          47          62          45          60
  GLENDO PROJECT USERS      91          94          70         130          97
  KENDRICK PROJECT          68          69          67         102          99
  NORTH PLATTE PROJ         99         100          74         133          99
To May 1997 Basin Outlook Report Contents Page