Shoshone and Clarks Fork River Basin (5)
March 1999

Snow
Snow Water Equivalent (SWE) is 134 percent of average (144 percent of last year) in the Shoshone River basin. The Clarks Fork River basin SWE is 125 percent of average (149 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 February was 145 percent of normal (396 percent of last February). Monthly percentages range from 0 to 218. The basin year-to-date precipitation is now 138 percent of average (139 percent of last year). Year to date percentages range from 22 to 167.

Reservoir
Current storage in Buffalo Bill Reservoir is 112 percent of average (83 percent of last year's storage and 68 percent of capacity. Currently, 436,900 acre-feet is stored in the reservoir compared to 525,900 acre feet last year. 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 645,000 acre-feet (109 percent of average). 

==================================================================================================================================
                                               SHOSHONE & CLARKS FORK RIVER BASINS
                                               Streamflow Forecasts - March 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       537       580    |      610       117    |       640       683            520
                                                                    |                       |
SF SHOSHONE RIVER nr Valley          APR-SEP       235       268    |      290       108    |       312       345            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP       182       234    |      270       118    |       306       358            229
                                                                    |                       |
BUFFALO BILL DAM Inflow (2)          APR-SEP       748       839    |      900       112    |       961      1052            804
                                                                    |                       |
CLARKS FORK RIVER nr Belfry          APR-SEP       552       607    |      645       109    |       683       738            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of February              |        Watershed Snowpack Analysis - March 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    436.9    525.9    391.2 |   SHOSHONE RIVER              6       144       134
                                                                        |
                                                                        |   CLARKS FORK in WY           7       149       125
                                                                        |
==================================================================================================================================
 * 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.
(D) - The operational measurement of flow at this point has been discountinued.
To March 1999 Basin Outlook Report Contents Page.