Shoshone and Clarks Fork River Basin (5)
February 1998

Snow
Snow Water Equivalent (SWE) is 131 percent of average (121 percent of last year) in the Shoshone River basin. The Clarks Fork River basin SWE is 121 percent of average (124 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 January was 163 percent of normal (104 percent of last January). Monthly percentages range from 10 to 203. The basin year-to-date precipitation is now 134 percent of average (119 percent of last year). Year to date percentages range from 22 to 162.

Reservoir
Current storage in Buffalo Bill Reservoir is 107 percent of average. Currently, 445,000 acre-feet is stored in the reservoir. This is 83 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 drainages should be above average this season. The fifty percent yield (April through September period) for North Fork Shoshone River at Wapiti is expected to be 610,000 acre-feet (117 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 290,000 acre-feet (108 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 270,000 acre-feet (118 percent of average). At the Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 900,000 acre-feet (112 percent of average). The fifty-percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 620,000 acre-feet (105 percent of average). 

  
==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - February 1, 1999
==================================================================================================================================
                                              |  <<====== 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       520       574    |      610       117    |       646       700            520
                                                                    |                       |
SF SHOSHONE RIVER nr Valley          APR-SEP       235       268    |      290       108    |       312       345            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP       192       238    |      270       118    |       302       348            229
                                                                    |                       |
BUFFALO BILL DAM Inflow (2)          APR-SEP       707       822    |      900       112    |       978      1093            804
                                                                    |                       |
CLARKS FORK RIVER nr Belfry          APR-SEP       520       580    |      620       105    |       660       720            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of January               |        Watershed Snowpack Analysis - February 1, 1999
==================================================================================================================================
                                      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    445.0    535.8    416.0 |   SHOSHONE RIVER              6       121       131
                                                                        |
                                                                        |   CLARKS FORK in WY           7       124       121
                                                                        |
==================================================================================================================================
 * 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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