Upper Green River Basin (11)
May 1998

Snow
The Upper Green River Basin snow water equivalent (SWE), above Fontenelle Reservoir, is 85 percent of average (57 percent of last year). SWE for the Green River above Warren Bridge is 85 percent of average and 57 percent of last year at this time. SWE on the west side of the Upper Green River basin is about 86 percent of normal, 56 percent of this time last year. Newfork River SWE is about 83 percent of normal -- about 62 percent of last year at this time. SWE for Big Sandy - Eden Valley area is 85 percent of normal and 61 percent of last year. For more information see the Basin Summary of Snow Courses at the beginning of this report.

Precipitation
The 13 reporting precipitation sites in the basin were 90 percent of average for April; precipitation was 80 percent of last year at this time. April precipitation varied from 51 percent of normal (Triple Peak SNOTEL) to 135 percent of normal (Big sandy Opening SNOTEL). Water year-to-date precipitation is about 80 percent of average (66 percent of last year).

Reservoir
Big Sandy Reservoir is storing 28,700 acre feet (120 percent of average and 75 percent of capacity). Eden is storing 5,200 acre feet (88 percent of average and 44 percent of capacity). Fontenelle Reservoir is storing about 131,600 acre feet (81 percent of average and about 38 percent of capacity). The 3,749,000 acre feet capacity Flaming Gorge reservoir contains about 3,190,600 acre feet; this year compared to 3,087,000 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
The fifty percent chance April through July runoff in the upper Green River basin is forecast below average. Green River at Warren Bridge is expected to yield about 250,000 acre feet (94 percent of normal). Pine Creek above Fremont Lake is expected to yield 100,000 acre feet (96 percent of normal). New Fork River near Big Piney is expected to yield about 350,000 acre feet (91 percent of normal). The 50 percent chance inflow to Fontenelle Reservoir is about 750,000 acre feet, which is about 88 percent of normal. Big Sandy near Farson is expected to be about 50,000 acre feet (88 percent of normal).


==================================================================================================================================
                                                     UPPER GREEN RIVER BASIN
                                               Streamflow Forecasts - May 1, 1998
==================================================================================================================================
                                              |  <<====== 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 R at Warren Bridge             APR-JUL       210       235    |      250        94    |       265       290            266
                                                                    |                       |
PINE CK abv Fremont Lake             APR-JUL        87        97    |      100        96    |       103       113            104
                                     MAY-JUL        85              |       97        96    |                 110            101
                                                                    |                       |
NEW FORK R nr Big Piney              APR-JUL       254       333    |      350        91    |       367       447            385
                                                                    |                       |
FONTENELLE RESERVOIR INFLOW          APR-JUL                        |      750        88    |                                849
                                                                    |                       |
BIG SANDY R nr Farson                APR-JUL        36        44    |       50        88    |        56        64             57
                                                                    |                       |
==================================================================================================================================
                         UPPER GREEN RIVER BASIN                        |                 UPPER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1998
==================================================================================================================================
                                      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     28.7     30.9     23.9 |   GREEN above Warren Bridge   4        57        85
                                                                        |
EDEN                                    11.8      5.2      7.2      5.9 |   UPPER GREEN (West Side)     7        56        86
                                                                        |
FLAMING GORGE                         3749.0   3190.6   3087.0      --- |   NEWFORK RIVER               2        62        83
                                                                        |
FONTENELLE                             344.8    131.6    134.1    161.8 |   BIG SANDY/EDEN VALLEY       2        61        85
                                                                        |
                                                                        |   GREEN above Fontenelle     13        57        85
                                                                        |
==================================================================================================================================
 * 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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