Shoshone and Clarks Fork River Basin (5)
April 1998

Snow
Snow Water Equivalent (SWE) is 94 percent of average (62 percent of last year) in the Shoshone River basin. Clarks Fork River basin SWE is 84 percent of average (57 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 113 percent of normal (110 percent of last March). National Weather Service station Clark 7NE had the lowest percentage of average for the month (13 percent). Sylvan Road SNOTEL had the highest percentage of average for the month (169 percent). The basin year-to-date precipitation is now 101 percent of average (66 percent of last year).

Reservoir
Current storage in Buffalo Bill Reservoir is 144 percent of average. Currently 518,400 acre feet is stored in the reservoir. This is 122 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 near average this season. The fifty percent yield (April through September period) for North Fork Shoshone River at Wapiti is expected to be 530,000 acre feet (102 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 260,000 acre feet (97 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 230,000 acre feet (100 percent of average). Below Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 760,000 acre feet (95 percent of average). The fifty percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 485,000 acre feet (82 percent of average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - April 1, 1998
==================================================================================================================================
                                              |  <<====== 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       431       490    |      530       102    |       570       629            520
                                                                    |                       |
SF SHOSHONE RIVER near Valley        APR-SEP       213       241    |      260        97    |       279       307            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP       154       199    |      230       100    |       261       306            229
                                                                    |                       |
SHOSHONE RIVER blw Buffalo Bill (2)  APR-SEP       608       698    |      760        95    |       822       912            804
                                                                    |                       |
CLARKS FORK RIVER near Belfry        APR-SEP       385       444    |      485        82    |       526       585            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 1998
==================================================================================================================================
                                      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    518.4    424.0    359.0 |   SHOSHONE RIVER              6        62        94
                                                                        |
                                                                        |   CLARKS FORK in WY           7        57        84
                                                                        |
==================================================================================================================================
 * 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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