Wyoming Water Supply Outlook Report
May 2001

Precipitation for April was variable across for the State. Year-to-date precipitation is generally well below average for the State. Precipitation ranged from 50 percent above average to about 40 percent below average, with about 2/3 of the basins being above the April average. Reservoir levels vary from about 46 percent of average to 156 percent of average, the exception being Eden Reservoir, which is too low to measure. Generally, the larger capacity reservoirs are above average storage. Forecast runoff varies from 16 to 87 percent of average. The mean of all the forecast points in the State is about 55 percent of average.

Snowpack
SWE is below to much below average for the entire State. SWE in the northwestern portion of the State is about 50 percent of average (79 percent of last year). Northeast Wyoming SWE is currently about 59 percent of average (79 percent of last year). The southeast portion is currently about 75 percent of average SWE (100 percent of last year). And the southwest is about 59 percent of average (95 percent of last year).

Precipitation
April precipitation was a mixed bag across the State. The Yellowstone and Madison River Basin received 154 percent of average precipitation during April. The Belle Fourche River Basin came in at only 53 percent of average for the month, but this was based solely on one SnoTel station. The following table displays the major river basins and their departure from normal for this month.

Streams
Stream flow yield is expected to be below average across the State, and well below average in the northern half of the State. Most probable yield for the State is forecast to be about 56 percent of average (varies from 16 to 71 percent of average). The northwest part of the State is expected to yield about 56 percent of normal -- yield estimates vary from 37 to 72 percent of normal through the northwest region of the State. Yield from the northeast portion of Wyoming will be below average (about 54 percent of average) -- yield estimates vary from 32 to 75 percent of average for the various forecast points. The southeast portion of the state will be about 59 percent of normal -- yield estimates range from 16 to 87 percent of normal. The southwest portion of Wyoming yield will be much below normal (about 55 percent of average), and estimates vary from 20 to 78 percent of average.

Reservoirs
The following reservoir data is based on the usable capacity of each reservoir. Although several reservoirs did not report, reservoir storage for those reporting is generally near or above average for about 2/3 of the listed reservoirs. See following table for further information about reservoir storage.

 

                             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   2001


 BASIN AREA         CURRENT AS  LAST YR AS  AVERAGE AS  CURRENT AS  CURRENT AS
  RESERVOIR         % CAPACITY  % CAPACITY  % CAPACITY   % AVERAGE   % LAST YR
--------------------------------------------------------------------------------
  ALCOVA                    97         107          98          99          90
  ANGOSTURA                 95          99          93         102          96
  BELLE FOURCHE            102         106          82         124          95
  BIG SANDY                 29          64          62          46          45
  BIGHORN LAKE              62          65          58         107          96
  BOYSEN                    73          84          84          87          87
  BUFFALO BILL              54          67          52         105          82
  BULL LAKE                 41          62          53          77          66
  DEERFIELD                 99         100          89         110          99
  EDEN                                      NO REPORT
  ENNIS LAKE                76          78          86          88          97
  FLAMING GORGE                       AVERAGE NOT ESTABLISHED
  FONTENELLE                34          34          47          72          99
  GLENDO                    92         102          90         102          90
  GRASSY LAKE               88          86          77         115         103
  GUERNSEY                  58          79          72          81          74
  HEBGEN LAKE               77          81          65         118          95
  JACKSON LAKE              78          85          54         145          93
  KEYHOLE                   88          91          57         156          97
  PACTOLA                   98         100          87         113          98
  PALISADES                 61          83          68          90          74
  PATHFINDER                76          98          60         127          78
  PILOT BUTTE               78          79          95          82          99
  SEMINOE                   65          74          39         169          88
  SHADEHILL                 98          69          80         123         143
  TONGUE RIVER              56          52          46         122         108
  VIVA NAUGHTON RES                         NO REPORT
  WHEATLAND #2              54          78          56          97          69
  WOODRUFF NARROWS                    AVERAGE NOT ESTABLISHED
  GLENDO PROJECT USERS      94          94          70         134         100
  KENDRICK PROJECT          80          87          67         119          92
  NORTH PLATTE PROJ         74         101          74         100          73