Shoshone and Clarks Fork River Basin (5)
June 1997

Snow
Snow in the basin is still high in percentage of average. SWE is 122 percent of average (65 percent of last year) in the Shoshone River basin, and 139 percent of average (16 percent below last year) in the Clarks Fork drainage. All sites, except for Younts Peak and White Mill, below 9000 feet have melted out as of June 1. 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 20 percent below normal. Sylvan Road had the lowest percentage of average for the month (44%). Year-to-date precipitation figures for the basin high. They range from 48 percent at Heart Mountain to 175 percent of average at Parkers Peak. The basin year-to-date precipitation is now 141 percent of average (7 percent less than last year).

Reservoir
Current storage in Buffalo Bill Reservoir is about 11 percent below average. Currently 335,900 acre feet is stored in Buffalo Bill Reservoir (about 89 percent of average). This is 97 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 above average this season. The fifty percent yield (June through September period) for North Fork at Wapiti is expected to be 480,000 acre feet (32 percent more than normal). South Fork of the Shoshone near Valley has an estimated yield of about 126,000 acre feet (26 percent above normal) and South Fork above Buffalo Bill Reservoir the fifty percent chance yield it is expected to be 245,000 (34 percent more than normal). Below Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 755,000 acre feet (25 percent above average). The fifty percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 565,000 acre feet (25 percent above average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - June 1, 1997
==================================================================================================================================
                                              |  <<====== 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       423       457    |      480       132    |       503       537            365
                                                                    |                       |
SF SHOSHONE RIVER near Valley        JUN-SEP       236       256    |      270       126    |       284       304            215
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   JUN-SEP       185       215    |      235       134    |       255       285            175
                                                                    |                       |
SHOSHONE RIVER blw Buffalo Bill (2)  JUN-SEP       667       719    |      755       125    |       791       843            606
                                                                    |                       |
CLARKS FORK RIVER near Belfry        JUN-SEP       487       534    |      565       125    |       596       643            453
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 1, 1997
==================================================================================================================================
                                      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    335.9    346.7    375.6 |   SHOSHONE RIVER              5        65       122
                                                                        |
                                                                        |   CLARKS FORK in WY           7        84       139
                                                                        |
==================================================================================================================================
 * 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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