Lower Green River Basin (12)
May 1998

Snow
The Blacks Fork drainage snow water equivalent (SWE) is 117 percent of average (121 % of last year). SWE in the Hams Fork, as of May 1, is 85 percent of average (57% of last year). Henry's Fork is 216 percent of the May 1 average (141 % of last year). The basin as a whole is 97 percent of average (68 % of last year). For more information see Basin Summary of Snow Courses at beginning of this report.

Precipitation
Precipitation was below average for the four reporting stations during April. Precipitation ranged from 67 percent of average at Indian Creek SNOTEL to 94 percent of average at Rock Springs FAA. The entire basin received 79 percent of average for the month (38 percent of last year). The basin year-to-date precipitation is currently 84 percent of average (62 % of last year).

Reservoir
Fontenelle Reservoir is currently storing 131,600 acre feet; this is 38 percent of capacity (98 % of last year). Flaming Gorge is storing 3,190,600 acre feet (no average established). Flaming Gorge has a maximum capacity of 3,749,00 acre feet. Viva Naughton is storing 30,500 acre feet; this is 72 percent of capacity (258% of last year).

Streamflow
Expected yields vary for 80 to 113 percent of average across the basin. The following forecast values are based on a 50 percent chance probability for the April to July forecast period. Green River near Green River is forecast to yield 765,000 acre feet (85 percent of average). Meeks Cabin Reservoir inflow is estimated to flow 103,000 acre feet (107 percent of average). Yield for the State Line Reservoir inflow will be about 33,000 acre feet (110 percent of average). The estimated yield for Hams Fork near Frontier is 51,000 acre feet (77 percent of average). Viva Naughton Reservoir inflow will be about 66,000 acre feet (71 percent of average). Flaming Gorge Reservoir inflow should be near 1,100,000 acre feet (92 percent of average). 


==================================================================================================================================
                                                     LOWER 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 nr Green River, WY           APR-JUL       647       717    |      765        85    |       813       883            899
                                                                    |                       |
MEEKS CABIN RESERVOIR Inflow         APR-JUL        90        98    |      103       107    |       108       116             96
                                                                    |                       |
STATE LINE RESERVOIR INFLOW          APR-JUL        26        30    |       33       110    |        36        40             30
                                                                    |                       |
HAMS FORK nr Frontier                APR-JUL        39        46    |       51        77    |        57        65             66
                                                                    |                       |
VIVA NAUGHTON RES inflow             APR-JUL        47        58    |       66        71    |        74        85             93
                                                                    |                       |
FLAMING GORGE RES INFLOW             APR-JUL                        |     1100        92    |                               1196
                                                                    |                       |
==================================================================================================================================
                         LOWER GREEN RIVER BASIN                        |                 LOWER 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
========================================================================|=========================================================
FONTENELLE                             344.8    131.6    134.1    161.8 |   HAMS FORK RIVER             4        57        85
                                                                        |
FLAMING GORGE                         3749.0   3190.6   3087.0      --- |   BLACKS FORK                 5       121       117
                                                                        |
VIVA NAUGHTON RES                       42.4     30.5     11.8     26.5 |   HENRYS FORK                 3       141       216
                                                                        |
                                                                        |   GREEN above Flaming Gorge  25        68        97
                                                                        |
==================================================================================================================================
 * 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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