Lower Green River Basin (12)
April 1999

Snow
The Blacks Fork drainage snow water equivalent (SWE) is 89 percent of average (83 % of last year). SWE in the Hams Fork, as of April 1, is 101 percent of average (117% of last year). Henry's Fork is 78 percent of average (58 percent of last year). The basin, as a whole, is 101 percent of average (110 % of last year). For more information see Basin Summary of Snow Courses at beginning of this report.

Precipitation
Precipitation varied widely for the 4 reporting stations during March. Precipitation ranged from 77 to 577 percent of average for the month. The entire basin received 125 percent of average for the month (88 percent of last year). The basin year-to-date precipitation is currently 97 percent of average (115 percent of last year). Year to date percentages range from 81 to 196.

Reservoir
Fontenelle Reservoir is currently storing 122,900 acre feet; this is 78 percent of average (106 % of last year). Flaming Gorge is currently storing 3,190,000 acre feet (at this time last year the reservoir was storing 3,235,000 acre feet). Flaming Gorge has a maximum capacity of 3,749,000 acre feet. Viva Naughton is currently storing 29,678,acre feet.

Streamflow
Expected yields vary from 83 to 105 percent of average across the basin. The following forecast values are based on a 50 percent chance probability for the April through July forecast period. Green River near Green River is forecast to yield about 930,000-acre feet (103 percent of average). Blacks Fork near Robertson is forecast to yield 83,000 acre-feet (87 percent of average). East Fork of Smiths Fork near Robertson is estimated to yield 25,000 acre-feet (83 percent of average). The estimated yield for Hams Fork near Frontier is 63,000- acre feet (96 percent of average). Viva Naughton Reservoir inflow will be about 80,000-acre feet (90 percent of average). Flaming Gorge Reservoir inflow is expected to yield 1,250,000 acre-feet (105 percent of average). 

==================================================================================================================================
                                                     LOWER GREEN RIVER BASIN
                                               Streamflow Forecasts - April 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 nr Green River, WY       APR-JUL       764       843    |      930       103    |      1017      1097            899
                                                                    |                       |
Blacks Fork nr Robertson             APR-JUL        60        74    |       83        87    |        92       106             95
                                                                    |                       |
EF of Smiths Fork nr Robertson       APR-JUL      19.8        23    |       25        83    |        28        32             30
                                                                    |                       |
Hams Fk blw Pole Ck nr Frontier      APR-JUL        45        56    |       63        96    |        71        84             66
                                                                    |                       |
Hams Fk Inflow to Viva Naughton Res  APR-JUL        54        69    |       80        90    |        91       106             89
                                                                    |                       |
Flaming Gorge Reservoir Inflow       APR-JUL       909      1128    |     1250       105    |      1372      1591           1196
                                                                    |                       |
==================================================================================================================================
                         LOWER GREEN RIVER BASIN                        |                 LOWER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 1999
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
FONTENELLE                             344.8    122.9    115.6    157.9 |   HAMS FORK RIVER             4       117       101
                                                                        |
FLAMING GORGE                         3749.0   3190.6   3235.0      --- |   BLACKS FORK                 5        83        89
                                                                        |
VIVA NAUGHTON RES                               NO REPORT               |   HENRYS FORK                 3        58        78
                                                                        |
                                                                        |   GREEN above Flaming Gorge  26       110       101
                                                                        |
==================================================================================================================================
 * 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.
(D) - The operational measurement of flow at this point has been discountinued.
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