May 1997 Water Supply Outlook - Upper Green River Basin

Upper Green River Basin
May 1997

Snow
Snow water equivalent (SWE) in the basin, as of May 1 is 141 percent of average. SWE for the Green River above Warren Bridge is 149 percent of average and 9 percent more than last year. SWE on the west side of the Upper Green River basin is about 53 percent more than normal, 10 percent more than last year. SWE in the New Fork drainage is 34 percent more than normal, which is about 20 percent more than last year. The Big Sandy and Eden Valley portion of the river basin is about 40 percent above normal and 23 percent more than last year. SWE for the Green River above Fontenelle Reservoir is 49 percent above average and 11 percent more than 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 averaged near normal (118 percent of average) for April; precipitation was 11 percent more than April of last year. April precipitation varied from 28 percent below normal (Pinedale) to 162 percent above normal (Fontenelle Dam). Water year-to-date precipitation, is 21 percent above normal (13 percent more than last year).

Reservoir
Big Sandy Reservoir is storing 30,900 acre feet (29 percent above normal) and Eden is storing 7,200 acre feet (22 percent above average). Fontenelle Reservoir is about 17 percent below average (120,800 acre feet). Flaming Gorge Reservoir has about 3,087,000 acre feet stored ( no average available). 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 basin, is forecast above average to much above average. Green River at Warren Bridge is expected to yield about 340,000 acre feet (28 percent more than normal). Pine Creek above Fremont Lake is expected to yield 130,000 acre feet ( 25 percent more than normal). New Fork River near Big Piney is expected to yield about 550,000 acre feet or 43 percent more than normal. The 50 percent chance inflow to Fontenelle Reservoir is about 1,250,000 acre feet, which is about 47 percent more than normal. Big Sandy near Farson is expected to be about 75,000 acre feet (32 percent more than normal).

==================================================================================================================================
                                                     UPPER GREEN RIVER BASIN
                                               Streamflow Forecasts - May 1, 1997
==================================================================================================================================
                                              |  <<====== 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       301       322    |      340       128    |       358       380            266
                                                                    |                       |
PINE CK abv Fremont Lake             APR-JUL       116       127    |      130       125    |       133       144            104
                                                                    |                       |
NEW FORK R nr Big Piney              APR-JUL       454       533    |      550       143    |       567       647            385
                                                                    |                       |
FONTENELLE RESERVOIR INFLOW          APR-JUL      1104      1202    |     1250       147    |      1298      1401            849
                                                                    |                       |
BIG SANDY R nr Farson                APR-JUL        63        70    |       75       132    |        80        87             57
                                                                    |                       |
==================================================================================================================================
                         UPPER GREEN RIVER BASIN                        |                 UPPER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1997
==================================================================================================================================
                                      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     30.9     33.0     23.9 |   GREEN above Warren Bridge   4       109       149
                                                                        |
EDEN                                    11.8      7.2      6.5      5.9 |   UPPER GREEN (West Side)     7       110       153
                                                                        |
FLAMING GORGE                         3749.0   3087.0   3107.3      --- |   NEWFORK RIVER               3       120       134
                                                                        |
FONTENELLE                             344.8    134.1    112.1    161.8 |   BIG SANDY/EDEN VALLEY       2       123       140
                                                                        |
                                                                        |   GREEN above Fontenelle     14       111       149
                                                                        |
==================================================================================================================================
 * 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.

To May 1997 Basin Outlook Report Contents Page

Upper Green River Basin May 1997

Upper Green River Basin
May 1997