Bighorn River Basin (4)
May 1998

Snow
The Nowood drainage SWE is 72 percent of last year and 95 percent of the May 1 average. Greybull River drainage SWE is 119 percent of average (86 percent of last year). Shell Creek SWE is 98 percent of average (85 percent of last year). The basin SWE, as a whole, is currently 100 percent of average (81 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
April precipitation was 117 percent of the monthly average (108 percent of last year). Bear Trap Meadow was the station reporting the highest percentage of average for April (175 percent of average). Lovell had the lowest percentage of average (30 percent). Year-to-date precipitation is 110 percent of normal; that is 100 percent of last year at this time.

Reservoir
Boysen Reservoir is currently storing 450,800 acre feet (90 percent of average). Bighorn Lake is now at 105 percent of average (830,700 acre feet). Boysen is currently storing 118 percent of last year at this time and Big Horn Lake is storing 119 percent of last year's volume.

Streamflow
The 50 percent chance May through September runoff is anticipated to be near normal. The Wind River below Boysen is forecast to yield 745,000 acre feet (98 percent of average); the Nowood River near Ten Sleep should yield near 43,000 acre feet (90 percent of normal); the Greybull River at Meeteese should yield 200,000 acre feet (103 percent of average); Shell Creek near Shell should yield 70,000 acre feet (97 percent of average) and the Bighorn River at Kane should yield 1,040,000 acre feet (100 percent of average). 

==================================================================================================================================
                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - May 1, 1998
==================================================================================================================================
                                              |  <<====== 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)
====================================================================|=======================|=====================================
WIND RIVER below Boysen (2)          MAY-SEP       486       640    |      745        98    |       850      1004            758
                                                                    |                       |
NOWOOD RIVER near Tensleep           MAY-SEP        21        34    |       43        90    |        52        66             48
                                                                    |                       |
GREYBULL RIVER at Meeteetse          MAY-SEP       168       187    |      200       103    |       213       232            195
                                                                    |                       |
SHELL CREEK near Shell               MAY-SEP        60        66    |       70        97    |        74        80             72
                                                                    |                       |
BIGHORN RIVER at Kane (2)            MAY-SEP       664       888    |     1040       100    |      1192      1416           1039
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1998
==================================================================================================================================
                                      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    450.8    381.3    502.6 |   NOWOOD RIVER                4        75       101
                                                                        |
BIGHORN LAKE                          1356.0    830.7    700.8    789.2 |   GREYBULL RIVER              2        86       119
                                                                        |
                                                                        |   SHELL CREEK                 4        85        98
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)   10        81       102
                                                                        |
==================================================================================================================================
 * 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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