Shoshone and Clarks Fork River Basin (5)
June 1999

Snow
Snow Water Equivalent (SWE) is 153 percent of the June 1 average (250 percent of last year) in the Shoshone River basin. The Clarks Fork River basin SWE is 117 percent of the June 1 average (189 percent of last year). For more information see the Basin Summary of Snow Course Data at the beginning of this report.

Precipitation
Precipitation for the month of May was 82 percent of normal (137 percent of last April). Monthly percentages range from 26 to 108 percent of average. The basin year-to-date precipitation is now 120 percent of average (136 percent of last year). Year-to-date percentages range from 52 to 161 percent of average.

Reservoir
Current storage in Buffalo Bill Reservoir is 104 percent of average (73 percent of last year's storage. Currently, about 392,100 acre-feet (56 percent of capacity) are stored in the reservoir compared to 496,700 acre feet last year. Detailed reservoir data is shown on the following page and on the reservoir storage summary at the beginning of this report.

Streamflow
Runoff from all drainages should be above average this season. The fifty percent yield (June through September period) for North Fork Shoshone River at Wapiti is expected to be 490,000 acre-feet (134 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 275,000 acre-feet (128 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 225,000 acre-feet (129 percent of average). At the Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 745,000 acre-feet (123 percent of average). The fifty-percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 540,000 acre-feet (119 percent of average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - June 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)
====================================================================|=======================|=====================================
NF SHOSHONE RIVER at Wapiti          JUN-SEP       442       470    |      490       134    |       510       538            365
                                                                    |                       |
SF SHOSHONE RIVER nr Valley          JUN-SEP       203       246    |      275       128    |       304       347            215
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   JUN-SEP       126       185    |      225       129    |       265       324            175
                                                                    |                       |
BUFFALO BILL DAM Inflow (2)          JUN-SEP       657       709    |      745       123    |       781       833            606
                                                                    |                       |
CLARKS FORK RIVER nr Belfry          JUN-SEP       485       518    |      540       119    |       562       595            453
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 1, 1999
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
BUFFALO BILL                           646.6    392.1    496.7    375.6 |   SHOSHONE RIVER              5       250       153
                                                                        |
                                                                        |   CLARKS FORK in WY           7       189       117
                                                                        |
==================================================================================================================================
 * 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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