Shoshone and Clarks Fork River Basin (5)
April 2001

Snow
Snow Water Equivalent (SWE) is 58 percent of the April 1 average (67 percent of last year) in the Shoshone River basin. The Clarks Fork River basin SWE is 54 percent of average (59 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 March was 74 percent of normal (102 percent of last year). Monthly percentages range from 8 to 237 percent of average. The basin year-to-date precipitation is now 72 percent of average (76 percent of last year). Year-to-date percentages range from 40 to 135 percent of average.

Reservoir
Current usable storage in Buffalo Bill Reservoir is 100 percent of average (82 percent of last year's storage) - the reservoir is about 56 percent of capacity. Currently, about 358,400 acre-feet of usable storage is in the reservoir compared to 436,200 acre feet last year - normally the reservoir stores about 359,000 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 (April through September period) for North Fork Shoshone River at Wapiti is expected to be 290,000 acre-feet (56 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 125,000 acre-feet (47 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 94,000 acre-feet (41 percent of average). At the Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 450,000 acre-feet (56 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 (56 percent of average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - April 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          APR-SEP       253       275    |      290        56    |       317       357            520
                                                                    |                       |
SF SHOSHONE RIVER nr Valley          APR-SEP       103       116    |      125        47    |       144       171            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP        63        81    |       94        41    |       125       171            229
                                                                    |                       |
BUFFALO BILL DAM Inflow (2)          APR-SEP       365       415    |      450        56    |       512       602            804
                                                                    |                       |
CLARKS FORK RIVER nr Belfry          APR-SEP       280       310    |      330        56    |       366       419            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 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    358.4    436.2    359.0 |   SHOSHONE RIVER              7        67        58
                                                                        |
                                                                        |   CLARKS FORK in WY           7        59        54
                                                                        |
==================================================================================================================================
 * 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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