Shoshone and Clarks Fork River Basin (5)
June 1998

Snow
Snow Water Equivalent (SWE) is 61 percent of average (50 percent of last year) in the Shoshone River basin. Clarks Fork River basin SWE is 62 percent of average (44 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 59 percent of normal (66 percent of last May). The National Weather Service station, Buffalo Bill Dam, had the lowest percentage of average for the month (19 percent). Younts Peak had the highest percentage of average for the month (87 percent). The basin year-to-date precipitation is now 89 percent of average (63 percent of last year).

Reservoir
Current storage in Buffalo Bill Reservoir is 132 percent of average. Currently 496,700 acre feet is stored in the reservoir. This is 148 percent of last year's storage at this time. 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 drainage's should be near average this season. The fifty percent yield (June through September period) for North Fork Shoshone River at Wapiti is expected to be 290,000 acre feet (80 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 165,000 acre feet (77 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 125,000 acre feet (71 percent of average). Below Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 420,000 acre feet (69 percent of average). The fifty percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 330,000 acre feet (73 percent of average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               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)
====================================================================|=======================|=====================================
NF SHOSHONE RIVER at Wapiti          JUN-SEP       233       267    |      290        80    |       313       347            365
                                                                    |                       |
SF SHOSHONE RIVER near Valley        JUN-SEP       131       151    |      165        77    |       179       199            215
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   JUN-SEP        75       105    |      125        71    |       145       175            175
                                                                    |                       |
SHOSHONE RIVER blw Buffalo Bill (2)  JUN-SEP       332       384    |      420        69    |       456       508            606
                                                                    |                       |
CLARKS FORK RIVER near Belfry        JUN-SEP       252       299    |      330        73    |       361       408            453
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             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
========================================================================|=========================================================
BUFFALO BILL                           646.6    496.7    335.9    375.6 |   SHOSHONE RIVER              5        50        61
                                                                        |
                                                                        |   CLARKS FORK in WY           7        44        62
                                                                        |
==================================================================================================================================
 * 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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