Shoshone and Clarks Fork River Basin
January 1997

Snow
Snowfall in the basin has been very good this year. Snow water equivalent (SWE) is 197 percent of average (15 percent above last year) in the Shoshone River basin, and 196 percent of average (24 percent above last year) in the Clarks Fork drainage. All sites are reporting well above average snowpack as of January 1. For more information see the Basin Summary of Snow Course Data at the beginning of this report.

Precipitation
Precipitation for the month of December was very high. Nine sites reported in with over 300 percent of average for the month. Clarks was the highest reporting station, with 519 percent. The basin came in at 302 percent of average for the month. Year-to-date precipitation figures for the basin are also very high. They range from 100 percent at Buffalo Bill Dam to 224 percent of average at Evening Star. The basin year-to-date precipitation is now 193 percent of average (13 percent more than last year).

Reservoir
When current storage is compared to average for this time of the year, storage in Buffalo Bill Reservoir is about 17 percent above average. Current storage in Buffalo Bill Reservoir 512,100 acre feet, about 97 percent of last years storage amount. 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 much above average this season. The fifty percent yield (April to September Period) for North Fork at Wapiti is expected to be 850,000 acre feet (64 percent more than normal). South Fork of the Shoshone near Valley has an estimated 50 percent chance yield of about 415,000 acre feet (54 percent above normal) and at Buffalo Bill Reservoir the fifty percent chance yield it is expected to be 365,000 (59 percent more than normal). Below Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 1,250,000 acre feet (56 percent above average). The fifty percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 810,000 acre feet (37 percent above average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - January 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          APR-SEP       706       792    |      850       164    |       908       994            520
                                                                    |                       |
SF SHOSHONE RIVER near Valley        APR-SEP       346       387    |      415       154    |       443       484            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP       274       328    |      365       159    |       402       456            229
                                                                    |                       |
SHOSHONE RIVER blw Buffalo Bill (2)  APR-SEP      1047      1163    |     1250       156    |      1337      1350            799
                                                                    |                       |
CLARKS FORK RIVER near Belfry        APR-SEP       655       747    |      810       137    |       873       965            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 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    512.1    528.6    436.7 |   SHOSHONE RIVER              5       115       197
                                                                        |
                                                                        |   CLARKS FORK in WY           7       124       196
                                                                        |
==================================================================================================================================
 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual flow 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 flow - actual flow may be affected by upstream water management.
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