Wind River Basin (3)
May 1999

Snow
The Wind River basin has above average snow water equivalent (SWE) for this time of the year. The Wind River above Dubois is 135 percent of average (125 percent of last year). The Little Wind is 187 percent of average water content (151 percent of last year), and the Popo Agie drainage is about 161 percent of average (151 percent of last year). The Wind River basin, above Boysen Reservoir, SWE is about 155 percent of average (About 143 percent of last year). See the Basin Summary of Snow Course Data at the front of this report for details.

Precipitation
April precipitation in the basin varied from 110 to 461 percent of average. April precipitation for the basin was about 302 percent of average for the 11 reporting stations; that is about 285 percent of last April's amount. Water year-to-date precipitation is 108 percent of normal. The current water-year-to-date average is about 138 percent of last year at this time. Year to date figures range from 102 to 237 percent of average for the 11 reporting stations.

Reservoirs
Current storage varies from 64 to 125 percent of average. Bull Lake is currently storing about 99,900 acre feet (125 percent of average). Boysen Reservoir is storing about 474,800 acre feet (94 percent of average). Pilot Butte is storing 19,200 acre feet (64 percent of average). Bull Lake is about 66 percent of capacity, while Boysen is 80 percent of capacity, and Pilot Butte is 61 percent capacity.

Streamflow
Water supply is estimated to be above normal this year. The following values reflect the 50 percent chance yields for the May through September runoff period. In the upper portion of the drainage, Wind River near Dubois is expected to yield about 130,000 acre feet (about 123 percent of average). The Wind River above Bull Lake Creek is expected to yield 630,000 acre feet (113 percent of average). Wind River at Riverton will yield about 800,000 acre feet (131 percent of average). Boysen Reservoir inflow will yield about 1,085,000 acre feet (143 percent of normal). Bull Lake Creek near Lenore is expected to yield about 220,000 acre feet (123 percent of average). Little Popo Agie River near Lander is expected to yield about 67,000 acre feet (137 percent of average). South Fork of Little Wind near Fort Washakie will yield about 127,000 acre feet (163 percent of average). Little Wind River near Riverton will yield about 450,000 acre feet (149 percent of average).

==================================================================================================================================
                                                         WIND RIVER BASIN
                                               Streamflow Forecasts - May 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)
====================================================================|=======================|=====================================
WIND RIVER near Dubois (D)           MAY-SEP       118       125    |      130       137    |       135       142             95
                                                                    |                       |
WIND RIVER abv Bull Lake Cr (2)      MAY-SEP       554       599    |      630       123    |       661       706            511
                                                                    |                       |
WIND RIVER at Riverton (2)           MAY-SEP       622       728    |      800       131    |       872       978            609
                                                                    |                       |
BOYSEN Reservoir Inflow (2)          MAY-SEP       826       980    |     1085       143    |      1190      1344            758
                                                                    |                       |
BULL LAKE CR near Lenore (2)         MAY-SEP       191       208    |      220       123    |       232       249            179
                                                                    |                       |
LT POPO AGIE RIVER nr Lander         MAY-SEP        53        61    |       67       137    |        73        81             49
                                                                    |                       |
SF LT WIND nr Fort Washakie          MAY-SEP       107       119    |      127       163    |       135       147             78
                                                                    |                       |
LT WIND RIVER nr Riverton            MAY-SEP       332       402    |      450       149    |       498       568            303
                                                                    |                       |
==================================================================================================================================
                            WIND RIVER BASIN                            |                    WIND RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1999
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
BULL LAKE                              151.8     99.9     95.7     79.9 |   WIND RIVER above Dubios     7       125       135
                                                                        |
BOYSEN                                 596.0    474.8    450.8    502.6 |   LITTLE WIND                 2       151       187
                                                                        |
PILOT BUTTE                             31.6     19.2     24.6     30.1 |   POPO AGIE                   6       151       161
                                                                        |
                                                                        |   WIND above Boysen Resv     14       143       155
                                                                        |
==================================================================================================================================
 * 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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