Shoshone and Clarks Fork River Basin
April 1997

Snow
Snowfall in the basin has been very good this year. SWE is 152 percent of average (1 percent above last year) in the Shoshone River basin, and 148 percent of average (5 percent above last year) in the Clarks Fork drainage. All sites are reporting well above average snowpack as of April 1. For more information see the Basin Summary of Snow Course Data at the beginning of this report.

Precipitation
Precipitation for the month of March was 4 percent below normal. Parkers Peak had the highest percentage of average for the month (138%). Year-to-date precipitation figures for the basin are also very high. They range from 43 percent at Hart Mountain to 183 percent of average at Parkers Peak. The basin year-to-date precipitation is now 156 percent of average (2 percent more than last year).

Reservoir
Current storage in Buffalo Bill Reservoir is about 18 percent above average. Currently 424,000 acre feet is stored in Buffalo Bill Reservoir (about 90 percent of last year's 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 drainage's should be much above average this season. The fifty percent yield (April to September period) for North Fork at Wapiti is expected to be 860,000 acre feet (65 percent more than normal). South Fork of the Shoshone near Valley has an estimated yield of about 415,000 acre feet (54 percent above normal) and South Fork above Buffalo Bill Reservoir the fifty percent chance yield it is expected to be 350,000 (53 percent more than normal). Below Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 1,300,000 acre feet (63 percent above average). The fifty percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 840,000 acre feet (42 percent above average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - April 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       761       820    |      860       165    |       900       959            520
                                                                    |                       |
SF SHOSHONE RIVER near Valley        APR-SEP       368       396    |      415       154    |       434       462            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP       274       319    |      350       153    |       381       426            229
                                                                    |                       |
SHOSHONE RIVER blw Buffalo Bill (2)  APR-SEP      1148      1238    |     1300       163    |      1362      1452            799
                                                                    |                       |
CLARKS FORK RIVER near Belfry        APR-SEP       740       799    |      840       142    |       881       940            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 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    424.0    472.6    359.0 |   SHOSHONE RIVER              6       101       152
                                                                        |
                                                                        |   CLARKS FORK in WY           7       105       148
                                                                        |
==================================================================================================================================
 * 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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