Wyoming Water Supply Outlook Report
May 1998

General
Generally, snow water equivalent (SWE) across the state is below normal. Precipitation for April was below normal. Most of the precipitation did occur as snow. Because of carry-over storage, most of the reservoir levels are above average. Forecast runoff varies from near normal to well below normal, but generally yields are expected to be 5-15 percent below normal. Except for some irrigated areas that rely on direct diversion, irrigation water supplies should be adequate this year.

Snowpack
Snowpack over the State varied from above normal to well below normal. The northwest portion of the State is generally slightly below normal with some individual locations well above normal. The Wind River drainage is near normal, while the remaining portions of the northwest part of Wyoming are 10-15 percent below normal. SWE in the northeast part of Wyoming is 5 percent below normal in the Powder River drainage and 50 percent below normal in the Belle Fourche and Cheyenne River drainages. The southeast portion of the State is near normal to 85-90 percent of normal at the end of April. Portions of the southeast are 60-70 percent below normal. Generally, the southwest part of the State is average to slightly below average; the Henrys Fork drainage is much above normal, and the upper Green river basin is about 13 percent below normal. The Bear River drainage appears to have just below normal SWE.

Precipitation
Most basins across Wyoming received below average precipitation this month. Ten of the 13 basins were below average for the month of April. The following table displays the major river basins and their departure from normal.

BasinDeparture
from normal
BasinDeparture
from normal
Snake River -08%Upper North Platte River-30%
Yellowstone & Madison -18%Lower North Platte River-29%
Wind River +05%Little Snake River -28%
Bighorn +17%Upper Green River -10%
Shoshone & Clarks Fork -43%Lower Green River -21%
Powder & Tongue River +29%Upper Bear River -16%
Belle Fourche & Cheyenne-22%

Streams
Runoff is expected to vary from average to just below average across the state. The northwestern part of the state is expected to have yields varying from average to about 12 percent below average. The northeast portion of Wyoming varies from near average to about 15 percent below average (some areas will be nearly 24 percent below normal). In most cases, the southeast portion of the state will be near average to about 20 percent below normal (as much as 76 percent below normal in the lower portion of the Platte River drainage). The southwest portion of Wyoming varies from above average to 12 percent below average on the Green River drainage, while the Bear River will produce 10-20 percent below average yields.

Reservoirs
Reservoir storage varies from well below to well above average, however, the majority are average to above average for this time of the year. Even a below average runoff should fill most reservoirs. 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   1998


 BASIN AREA         CURRENT AS  LAST YR AS  AVERAGE AS  CURRENT AS  CURRENT AS
  RESERVIOR         % CAPACITY  % CAPACITY  % CAPACITY   % AVERAGE   % LAST YR
--------------------------------------------------------------------------------
  ALCOVA                    97          98          98         100          99
  ANGOSTURA                 99          99          93         106         100
  BELLE FOURCHE            103         100          82         126         103
  BIG SANDY                 75          81          62         120          93
  BIGHORN LAKE              61          52          58         105         119
  BOYSEN                    76          64          84          90         118
  BUFFALO BILL              76          46          52         147         167
  BULL LAKE                 63          53          53         120         119
  DEERFIELD                 96          97          89         107          99
  EDEN                      44          61          50          88          72
  ENNIS LAKE                80          80          86          93         100
  FLAMING GORGE                       AVERAGE NOT ESTABLISHED
  FONTENELLE                38          39          47          81          98
  GLENDO                    94          96          90         104          97
  GRASSY LAKE               49          90          77          64          55
  GUERNSEY                  70          68          72          97         102
  HEBGEN LAKE               70          63          65         107         111
  JACKSON LAKE              78          51          54         145         153
  KEYHOLE                   93          96          57         165          97
  PACTOLA                   98         101          87         112          97
  PALISADES                 65          19          68          96         350
  PATHFINDER                97          91          60         161         107
  PILOT BUTTE               78          75          95          82         103
  SEMINOE                   68          60          39         176         113
  SHADEHILL                 89          95          80         111          93
  TONGUE RIVER              15          26          54          27          56
  VIVA NAUGHTON RES         72          28          62         115         258
  WHEATLAND #2              80          72          56         144         111
  WOODRUFF NARROWS                    AVERAGE NOT ESTABLISHED
  GLENDO PROJECT USERS      91          91          70         130         100
  KENDRICK PROJECT          80          68          67         119         117
  NORTH PLATTE PROJ        104          99          74         140         105

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