Bighorn River Basin (4)
May 2001

Snow
Snowpack in this basin is well below average for this time of year. The Nowood drainage SWE is 59 percent of average (97 percent of last year). Greybull River SWE is 31 percent of average (60 percent of last year). Shell Creek SWE is 70 percent of average (78 percent of last year). The basin SWE, as a whole, is currently 61 percent of average (82 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
April precipitation was 88 percent of the monthly average (87 percent of last year). Sites ranged from 16 to 139 percent of average for the month. Year-to-date precipitation is 73 percent of normal; that is 80 percent of last year at this time. Year to date percentages, from the 13 reporting stations, range from 48 to 145.

Reservoir
Usable storage in Boysen Reservoir is currently 437,300-acre feet (87 percent of average). Bighorn Lake is now at 107 percent of average (841,200-acre feet). Boysen is currently storing 87 percent of last year at this time and Big Horn Lake is storing 96 percent of last year's volume.

Streamflow
The 50 percent chance May through September runoff is anticipated to be below normal. The Boysen Reservoir inflow is forecast to yield 320,000 acre feet (42 percent of average); the Greybull River nr Meeteese should yield 80,000 acre feet (41 percent of average); Shell Creek near Shell should yield 52,000 acre feet (72 percent of average) and the Bighorn River at Kane should yield 445,000 acre feet (43 percent of average). 

==================================================================================================================================
                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - May 1, 2001
==================================================================================================================================
                                              |  <<====== Drier ======  Future Conditions  =======  Wetter =====>>  |             
                                              |                                                                     |
  Forecast Point                     Forecast |  ==================== Chance Of Exceeding * ======================  |
                                      Period  |    90%       70%    |  50% (Most Probable)  |      30%       10%    |  30-Yr Avg.
                                              | (1000AF)  (1000AF)  |   (1000AF)  (% AVG.)  |    (1000AF)  (1000AF) |    (1000AF)
====================================================================|=======================|=====================================
BOYSEN RESERVOIR Inflow (2)          MAY-SEP       211       276    |      320        42    |       425       579            758
                                                                    |                       |
GREYBULL RIVER nr Meeteetse          MAY-SEP        64        73    |       80        41    |        96       120            195
                                                                    |                       |
SHELL CREEK nr Shell                 MAY-SEP        42        48    |       52        72    |        56        63             72
                                                                    |                       |
BIGHORN RIVER at Kane (2)            MAY-SEP       283       379    |      445        43    |       598       822           1039
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 2001
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
BOYSEN                                 596.0    437.3    501.4    502.6 |   NOWOOD RIVER                5        97        59
                                                                        |
BIGHORN LAKE                          1356.0    841.2    877.6    789.2 |   GREYBULL RIVER              2        60        31
                                                                        |
                                                                        |   SHELL CREEK                 4        78        70
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)   11        82        61
                                                                        |
==================================================================================================================================
 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual volume will exceed the volumes in the table.

The average is computed for the 1961-1990 base period.

(1) - The values listed under the 10% and 90% Chance of Exceeding are actually 5% and 95% exceedance levels.                  
(2) - The value is natural volume - actual volume may be affected by upstream water management.
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