Upper Green River Basin (11)
May 2000

Snow
The Upper Green River Basin snow water equivalent (SWE), above Fontenelle Reservoir, is 64 percent of average (51 percent of last year). The Green River basin SWE above Warren Bridge is 51 percent of normal (45 percent of last year). SWE on the west side of the Upper Green River basin is about 71 percent of normal, 55 percent of this time last year. Newfork River SWE is now 49 percent of normal (39 percent of last year). Big Sandy-Eden Valley SWE is about 71 percent of average (58 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 58 percent of the April average (32 percent of last year at this time). April precipitation varied from 17 to 122 percent of average. Water year-to-date precipitation is about 72 percent of average (69 percent of last year). Year to date percentage of average ranges from 66 to 85 for the reporting stations.

Reservoir
Data for Big Sandy Reservoir and Eden Reservoir were not reported this month. Fontenelle Reservoir is storing 118,600 acre-feet (73 percent of average and 30 percent of the total capacity). Flaming Gorge reservoir is currently storing 3,196,900 acre feet (85 percent of capacity). There is no average established for Flaming Gorge. 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 well below average. Green River at Warren Bridge is expected to yield about 215,000 acre-feet (81 percent of normal). Pine Creek above Fremont Lake is expected to yield 85,000 acre-feet (82 percent of normal). New Fork River near Big Piney is expected to yield about 285,000 acre-feet (74 percent of normal). Fontenelle Reservoir Inflow is estimated to be 575,000 acre-feet (68 percent of average), and Big Sandy near Farson is expected to be about 40,000 acre-feet (70 percent of normal). 

==================================================================================================================================
                                                     UPPER GREEN RIVER BASIN
                                               Streamflow Forecasts - May 1, 2000
==================================================================================================================================
                                              |  <<====== 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       178       200    |      215        81    |       230       252            266
                                                                    |                       |
Pine Creek abv Fremont Lake          APR-JUL        72        80    |       85        82    |        90        98            104
                                     MAY-JUL        66        74    |       79        78    |        84        92            101
                                                                    |                       |
New Fork River nr Big Piney          APR-JUL       200       251    |      285        74    |       319       370            385
                                                                    |                       |
Fontenelle Reservoir Inflow          APR-JUL       457       526    |      575        68    |       627       707            849
                                                                    |                       |
Big Sandy River nr Farson            APR-JUL        26        34    |       40        70    |        46        54             57
                                                                    |                       |
==================================================================================================================================
                         UPPER GREEN RIVER BASIN                        |                 UPPER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 2000
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
BIG SANDY                                       NO REPORT               |   GREEN above Warren Bridge   4        50        51
                                                                        |
EDEN                                            NO REPORT               |   UPPER GREEN (West Side)     7        55        71
                                                                        |
FLAMING GORGE                         3749.0   3196.9   3140.3      --- |   NEWFORK RIVER               2        39        49
                                                                        |
FONTENELLE                             344.8    118.6    134.1    161.8 |   BIG SANDY/EDEN VALLEY       2        58        71
                                                                        |
                                                                        |   GREEN above Fontenelle     13        51        64
                                                                        |
==================================================================================================================================
 * 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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