Shoshone and Clarks Fork River Basin (5)
April 1999

Snow
Snow Water Equivalent (SWE) is 121 percent of average (128 percent of last year) in the Shoshone River basin. The Clarks Fork River basin SWE is 113 percent of average (134 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 65 percent of normal (58 percent of last March). Monthly percentages range from 29 to 96 percent of average. The basin year-to-date precipitation is now 124 percent of average (123 percent of last year). Year-to-date percentages range from 17 to 152 percent of average.

Reservoir
Current storage in Buffalo Bill Reservoir is 112 percent of average (78 percent of last year's storage and 62 percent of capacity. Currently, 402,700 acre-feet is stored in the reservoir compared to 518,400 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 615,000 acre-feet (118 percent of average). South Fork of the Shoshone River near Valley is estimated to yield of 285,000 acre-feet (106 percent of average), and South Fork above Buffalo Bill Reservoir is expected to be 255,000 acre-feet (111 percent of average). At the Buffalo Bill Reservoir, the fifty percent chance yield for the Shoshone River is expected to be about 880,000 acre-feet (110 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 - April 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       548       588    |      615       118    |       642       682            520
                                                                    |                       |
SF SHOSHONE RIVER nr Valley          APR-SEP       239       266    |      285       106    |       304       331            269
                                                                    |                       |
SF SHOSHONE RIVER abv Buffalo Bill   APR-SEP       178       224    |      255       111    |       286       332            229
                                                                    |                       |
BUFFALO BILL DAM Inflow (2)          APR-SEP       728       818    |      880       110    |       942      1032            804
                                                                    |                       |
CLARKS FORK RIVER nr Belfry          APR-SEP       531       584    |      620       105    |       656       709            590
                                                                    |                       |
==================================================================================================================================
                   SHOSHONE & CLARKS FORK RIVER BASINS                  |           SHOSHONE & CLARKS FORK RIVER BASINS
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 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    402.7    518.4    359.0 |   SHOSHONE RIVER              6       128       121
                                                                        |
                                                                        |   CLARKS FORK in WY           7       134       113
                                                                        |
==================================================================================================================================
 * 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.
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