Bighorn River Basin (4)
May 1999

Snow
Snowpack in this basin is near average, except for the Greybull River drainage, which is 54 percent above average. The Nowood drainage is 97 percent (96 percent of last year). The Greybull River drainage SWE is 154 percent of average (130 percent of last year). Shell Creek SWE is 103 percent of average (105 percent of last year). The basin SWE, as a whole, is currently 107 percent of average (105 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
April precipitation was 178 percent of the monthly average (157 percent of last year). Sites ranged from 89 to 318 percent of average for the month. Year-to-date precipitation is 128 percent of normal; that is 119 percent of last year at this time. Year to date percentages, from the 15 reporting stations, range from 97 to 177.

Reservoir
Boysen Reservoir is currently storing 474,800-acre feet (94 percent of average). Bighorn Lake is now at 98 percent of average (771,300-acre feet). Boysen is currently storing 105 percent of last year at this time and Big Horn Lake is storing 93 percent of last year's volume.

Streamflow
The 50 percent chance May through September runoff is anticipated to be near normal. The Wind River at Boysen is forecast to yield 1,085,000 acre feet (143 percent of average); the Nowood River near Ten Sleep should yield near 36,000 acre feet (75 percent of normal); the Greybull River at Meeteese should yield 230,000 acre feet (118 percent of average); Shell Creek near Shell should yield 68,000 acre feet (94 percent of average) and the Bighorn River at Kane should yield 1,490,000 acre feet (143 percent of average). 

==================================================================================================================================
                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - May 1, 1999
==================================================================================================================================
                                              |  <<====== 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       826       980    |     1085       143    |      1190      1344            758
                                                                    |                       |
NOWOOD RIVER nr Tensleep (D)         MAY-SEP      10.4        26    |       36        75    |        46        62             48
                                                                    |                       |
GREYBULL RIVER nr Meeteetse          MAY-SEP       190       214    |      230       118    |       246       270            195
                                                                    |                       |
SHELL CREEK nr Shell                 MAY-SEP        58        64    |       68        94    |        72        79             72
                                                                    |                       |
BIGHORN RIVER at Kane (2)            MAY-SEP      1113      1337    |     1490       143    |      1643      1867           1039
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1999
==================================================================================================================================
                                      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    474.8    450.8    502.6 |   NOWOOD RIVER                5        96        97
                                                                        |
BIGHORN LAKE                          1356.0    771.3    830.7    789.2 |   GREYBULL RIVER              2       130       154
                                                                        |
                                                                        |   SHELL CREEK                 4       105       103
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)   11       105       107
                                                                        |
==================================================================================================================================
 * 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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