Bighorn River Basin (4)
January 1999

Snow
Snowpack in this basin is below average, except for the Greybull River drainage. The Nowood drainage is 75 percent (101 percent of last year). The Greybull River drainage SWE is 128 percent of average (92 percent of last year). Shell Creek SWE is 88 percent of average (94 percent of last year). The basin SWE, as a whole, is currently 92 percent of average (95 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
December precipitation was 98 percent of the monthly average (97 percent of last year). Sites ranged from 8 percent to 180 percent of average for the month. Year-to-date precipitation is 127 percent of normal; that is 123 percent of last year at this time. Year to date percentages, from the 15 reporting stations, range from 70 to 258.

Reservoir
Boysen Reservoir is currently storing 593,100-acre feet (97 percent of average). Bighorn Lake is now at 106 percent of average (944,100-acre feet). Boysen is currently storing 104 percent of last year at this time and Big Horn Lake is storing 98 percent of last year's volume.

Streamflow
The 50 percent chance April through September runoff is anticipated to be near normal. The Wind River at Boysen is forecast to yield 805,000 acre feet (100 percent of average); the Nowood River near Ten Sleep should yield near 75,000 acre feet (130 percent of normal); the Greybull River at Meeteetse should yield 216,000 acre feet (108 percent of average); Shell Creek near Shell should yield 71,000 acre feet (95 percent of average) and the Bighorn River at Kane should yield 1,120,000 acre feet (100 percent of average). 

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                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - June 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)          JUN-SEP       293       416    |      500        82    |       584       707            609
                                                                    |                       |
NOWOOD RIVER near Tensleep           JUN-SEP       8.0      10.4    |     12.0        57    |      13.6      16.0             21
                                                                    |                       |
GREYBULL RIVER at Meeteetse          JUN-SEP       121       126    |      130        78    |       134       139            167
                                                                    |                       |
SHELL CREEK near Shell               JUN-SEP        29        34    |       38        69    |        42        47             55
                                                                    |                       |
BIGHORN RIVER at Kane (2)            JUN-SEP       261       484    |      635        78    |       786      1009            811
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 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    447.6    420.9    546.4 |   NOWOOD RIVER                2         0         0
                                                                        |
BIGHORN LAKE                          1356.0    859.7    846.3    855.6 |   GREYBULL RIVER              2       233        13
                                                                        |
                                                                        |   SHELL CREEK                 3        45        44
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)    7        42        37
                                                                        |
==================================================================================================================================
 * 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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