Lower Green River Basin (12)
May 2000

Snow
The Blacks Fork drainage snow water equivalent (SWE) is 66 percent of average (61 % of last year). SWE in the Hams Fork, as of May 1, is 60 percent of average (49% of last year). The Henry's Fork SWE for the basin is 43 percent of average (30 % of last year). The basin, as a whole, is 88 percent of average (87 percent of last year). For more information see Basin Summary of Snow Courses at beginning of this report.

Precipitation
Precipitation was above average for the 3 reporting stations during April. Precipitation ranged from 38 to 140 percent of average for the month. The entire basin received 66 percent of average for the month (25 percent of last year). The basin year-to-date precipitation is currently 70 percent of average (65 percent of last year). Year to date percentages range from 65 to 76.

Reservoir
Fontenelle Reservoir is currently storing 118,600 acre feet; this is 73 percent of average (88 % of last year). Flaming Gorge does not have an average established. Flaming Gorge is currently storing 3,196,000 acre feet. Last year at this time there was 3,140,300 acre feet in storage at Flaming Gorge. Viva Naughton is currently storing 37,600 acre feet; this is 142 percent of average (129 % of last year).

Streamflow
Expected yields vary from 56 to 70 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 580,000-acre feet (65 percent of average). Blacks Fork near Robertson is forecast to yield 66,000-acre feet (70 percent of average). East Fork of Smiths Fork near Robertson is estimated to yield 19,800 acre-feet (66 percent of average). The estimated yield for Hams Fork near Frontier is 40,000-acre feet (61 percent of average). Viva Naughton Reservoir inflow will be about 50,000-acre feet (56 percent of average). Flaming Gorge Reservoir inflow will be about 775,000-acre feet (65 percent of average). 

==================================================================================================================================
                                                     LOWER GREEN RIVER BASIN
                                               Streamflow Forecasts - May 1, 2000
==================================================================================================================================
                                              |  <<====== 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       397       506    |      580        65    |       654       763            899
                                                                    |                       |
Blacks Fork nr Robertson             APR-JUL        50        60    |       66        70    |        72        82             95
                                                                    |                       |
EF of Smiths Fork nr Robertson       APR-JUL      16.8      18.5    |     19.8        66    |        21        23             30
                                                                    |                       |
Hams Fk blw Pole Ck nr Frontier      APR-JUL        29        36    |       40        61    |        45        52             66
                                                                    |                       |
Hams Fk Inflow to Viva Naughton Res  APR-JUL        31        42    |       50        56    |        58        69             89
                                                                    |                       |
Flaming Gorge Reservoir Inflow       APR-JUL       520       672    |      775        65    |       878      1030           1196
                                                                    |                       |
==================================================================================================================================
                         LOWER GREEN RIVER BASIN                        |                 LOWER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 2000
==================================================================================================================================
                                      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    118.6    134.1    161.8 |   HAMS FORK RIVER             4        49        60
                                                                        |
FLAMING GORGE                         3749.0   3196.9   3140.3      --- |   BLACKS FORK                 5        61        66
                                                                        |
VIVA NAUGHTON RES                       42.4     37.6     29.2     26.5 |   HENRYS FORK                 3        30        43
                                                                        |
                                                                        |   GREEN above Flaming Gorge  25        50        62
                                                                        |
==================================================================================================================================
 * 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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