Upper Green River Basin
April 1997

Snow
Snow water equivalent (SWE) in the basin, as of April 1, is 141 percent of average. SWE for the Green River above Warren Bridge is 150 percent of average and 17 percent more than last year. SWE on the west side of the Upper Green River basin is about 39 percent more than normal, 10 percent more than last year. SWE in the New Fork drainage is 38 percent more than normal, which is about 22 percent more than last year. The Big Sandy and Eden Valley portion of the river basin is about 45 percent above normal and 34 percent more than 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 averaged near normal (102 percent of average) for March; precipitation was 10 percent less than March of last year. March precipitation varied from 85 percent below normal (Farson) to 65 percent above normal (Gros Ventre Summit). Water year-to-date precipitation, is 21 percent above normal (12 percent more than last year).

Reservoir
Big Sandy Reservoir is storing 26,700 acre feet (34 percent above normal) and Eden is storing 6,100 acre feet (30 percent above average). Fontenelle Reservoir is about 23 percent below average (120,800 acre feet). Flaming Gorge Reservoir has about 3,184,900 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 80,000 acre feet (40 percent more than normal). 

==================================================================================================================================
                                                     UPPER GREEN RIVER BASIN
                                               Streamflow Forecasts - April 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       295       321    |      340       128    |       359       386            266
                                                                    |                       |
PINE CK abv Fremont Lake             APR-JUL       114       126    |      130       125    |       134       146            104
                                                                    |                       |
NEW FORK R nr Big Piney              APR-JUL       435       527    |      550       143    |       574       666            385
                                                                    |                       |
FONTENELLE RESERVOIR INFLOW          APR-JUL      1087      1192    |     1250       147    |      1308      1409            849
                                                                    |                       |
BIG SANDY R nr Farson                APR-JUL        66        74    |       80       140    |        86        94             57
                                                                    |                       |
==================================================================================================================================
                         UPPER GREEN RIVER BASIN                        |                 UPPER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 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     26.7      ---     19.9 |   GREEN above Warren Bridge   4       117       150
                                                                        |
EDEN                                    11.8      6.1      6.1      4.7 |   UPPER GREEN (West Side)     7       110       139
                                                                        |
FLAMING GORGE                         3749.0   3184.9   3151.0      --- |   NEWFORK RIVER               3       122       138
                                                                        |
FONTENELLE                             344.8    120.8     97.4    157.9 |   BIG SANDY/EDEN VALLEY       2       134       145
                                                                        |
                                                                        |   GREEN above Fontenelle     14       113       141
                                                                        |
==================================================================================================================================
 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual flow 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 flow - actual flow may be affected by upstream water management.
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