Shoshone and Clarks Fork River Basin (5)
May 2001

Snow
Snow Water Equivalent (SWE) is 54 percent of the May 1 average (78 percent of last year) in the Shoshone River basin. The Clarks Fork River basin SWE is 52 percent of average (69 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 April was 104 percent of normal (126 percent of last year). Monthly percentages range from 17 to 168 percent of average. The basin year-to-date precipitation is now 77 percent of average (82 percent of last year). Year-to-date percentages range from 41 to 102 percent of average.

Reservoir
Current usable storage in Buffalo Bill Reservoir is 105 percent of average (82 percent of last year's storage) - the reservoir is about 52 percent of capacity. Currently, about 352,100 acre-feet of usable storage is in the reservoir compared to 430,800 acre feet last year - normally the reservoir stores about 335,100 acre feet at this time of the year. Detailed reservoir data is shown on the following page and on the reservoir storage summary at the beginning of this report.

Streamflow
The fifty percent yield (May through September period) for North Fork Shoshone River at Wapiti is expected to be 335,000 acre-feet (70 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 140,000 acre-feet (54 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 81,000 acre-feet (37 percent of average). At the Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 440,000 acre-feet (58 percent of average). The fifty-percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 300,000 acre-feet (53 percent of average). 

 
==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - May 1, 2001
==================================================================================================================================
                                              |  <<====== 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          MAY-SEP       302       322    |      335        70    |       354       383            480
                                                                    |                       |
SF SHOSHONE RIVER nr Valley          MAY-SEP       121       132    |      140        54    |       154       176            259
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   MAY-SEP        60        72    |       81        37    |       104       138            218
                                                                    |                       |
BUFFALO BILL DAM Inflow (2)          MAY-SEP       363       409    |      440        58    |       494       573            754
                                                                    |                       |
CLARKS FORK RIVER nr Belfry          MAY-SEP       255       282    |      300        53    |       334       384            566
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 2001
==================================================================================================================================
                                      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    352.1    430.8    335.1 |   SHOSHONE RIVER              7        78        54
                                                                        |
                                                                        |   CLARKS FORK in WY           7        69        52
                                                                        |
==================================================================================================================================
 * 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.
To May 2001 Basin Outlook Report Contents Page