Upper Green River Basin (11)
May 1999

Snow
The Upper Green River Basin snow water equivalent (SWE), above Fontenelle Reservoir, is 125 percent of average (143 percent of last year). The Green River basin SWE above Warren Bridge is 114 percent of normal (121 percent of last year). SWE on the West Side of the Upper Green River basin is about 128 percent of normal, 150 percent of this time last year. Newfork River SWE is now 126 percent of normal (153 percent of last year). Big Sandy - Eden Valley SWE is currently 124 percent of normal (145 percent of last year). For more information see the Basin Summary of Snow Courses at the beginning of this report.

Precipitation
The 11 reporting precipitation sites in the basin were 184 percent of the April average (200 percent of last year at this time). April precipitation varied from 133 to 297 percent of average. Water year-to-date precipitation is about 104 percent of average (129 percent of last year). Year to date percentage of average ranges from 91 to 126 for the 11 reporting stations.

Reservoir
Big Sandy Reservoir is storing 37,800 acre-feet (158 percent of average and 99 percent of capacity). Eden reservoir is storing 8,700 acre-feet (144 percent of average and 72 percent of capacity). Fontenelle Reservoir is storing 134,100 acre-feet (83 percent of average and 39 percent of the total capacity). Flaming Gorge reservoir is presently storing about 3,140,300 acre-feet (reservoir capacity is 3,749,000 acre-feet). Detailed reservoir data is shown on the following page and on the reservoir storage summary at the beginning of this report.

Streamflow
The fifty percent chance April through July runoff in the Upper Green River basin is forecast above average. Green River at Warren Bridge is expected to yield about 310,000 acre-feet (117 percent of normal). Pine Creek above Fremont Lake is expected to yield 110,000 acre-feet (106 percent of normal). New Fork River near Big Piney is expected to yield about 450,000 acre-feet (117 percent of normal). Big Sandy near Farson is expected to be about 65,000 acre-feet (114 percent of normal).

 
==================================================================================================================================
                                                     UPPER GREEN 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)
====================================================================|=======================|=====================================
Green River at Warren Bridge         APR-JUL       271       295    |      310       117    |       325       351            266
                                                                    |                       |
Pine Creek abv Fremont Lake          APR-JUL        97       105    |      110       106    |       115       123            104
                                     MAY-JUL        96       104    |      109       108    |       114       122            101
                                                                    |                       |
New Fork River nr Big Piney          APR-JUL       354       416    |      450       117    |       484       547            385
                                                                    |                       |
Fontenelle Reservoir Inflow          APR-JUL       824       963    |     1030       121    |      1099      1240            849
                                                                    |                       |
Big Sandy River nr Farson            APR-JUL        51        59    |       65       114    |        71        79             57
                                                                    |                       |
==================================================================================================================================
                         UPPER GREEN RIVER BASIN                        |                 UPPER GREEN 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
========================================================================|=========================================================
BIG SANDY                               38.3     37.8     28.7     23.9 |   GREEN above Warren Bridge   4       121       114
                                                                        |
EDEN                                    11.8      8.5      5.2      5.9 |   UPPER GREEN (West Side)     7       150       128
                                                                        |
FLAMING GORGE                         3749.0   3140.3   3190.6      --- |   NEWFORK RIVER               2       153       126
                                                                        |
FONTENELLE                             344.8    134.1    131.6    161.8 |   BIG SANDY/EDEN VALLEY       2       145       124
                                                                        |
                                                                        |   GREEN above Fontenelle     13       143       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.

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