Shoshone and Clarks Fork River Basin (5)
January 1998

Snow
Snow in the basin is still below average for this time of year. SWE is 90 percent of average (46 percent of last year) in the Shoshone River basin, and 80 percent of average (41 percent of last year) in the Clarks Fork drainage. All sites, except for Marquette are below average for this time of year. For more information see the Basin Summary of Snow Course Data at the beginning of this report.

Precipitation
Precipitation for the month of December was 28 percent below normal. Buffalo Bill Dam had the lowest percentage of average for the month (34%). Year-to-date precipitation figures for the basin range from 39 percent at Clark to 168 percent of average at Cody. The basin year-to-date precipitation is now 98 percent of average (47 percent less than last year).

Reservoir Current storage in Buffalo Bill Reservoir is 125 percent of average. Currently 544,900 acre feet is stored in the reservoir. This is 106 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 could be below average this season. The fifty percent yield (June to September period) for North Fork at Wapiti is expected to be 440,000 acre feet (85 percent of average). South Fork of the Shoshone near Valley has an estimated yield of 220,000 acre feet (82 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 185,000 acre feet (81 percent of average). Below Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 630,000 acre feet (78 percent of average). The fifty percent chance yield for the Clarks Fork of the Yellowstone near Belfry, Montana is expected to be about 465,000 acre feet (79 percent above average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - January 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       296       382    |      440        85    |       498       584            520
                                                                    |                       |
SF SHOSHONE RIVER near Valley        APR-SEP       151       192    |      220        82    |       248       289            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP        94       148    |      185        81    |       222       276            229
                                                                    |                       |
SHOSHONE RIVER blw Buffalo Bill (2)  APR-SEP       415       543    |      630        78    |       717       845            804
                                                                    |                       |
CLARKS FORK RIVER near Belfry        APR-SEP       310       402    |      465        79    |       528       620            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 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    544.9    512.1    436.7 |   SHOSHONE RIVER              5        46        90
                                                                        |
                                                                        |   CLARKS FORK in WY           7        41        80
                                                                        |
==================================================================================================================================
 * 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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