Lower Green River Basin (12)
May 1999

Snow
The Blacks Fork drainage snow water equivalent (SWE) is 109 percent of average (93 % of last year). SWE in the Hams Fork, as of May 1, is 125 percent of average (148% of last year). SWE in the Henry's Fork is 141 percent of average (65 percent of last year). SWE for the basin, as a whole, is 123 percent of average (125 % of last year). For more information see Basin Summary of Snow Courses at beginning of this report.

Precipitation
Precipitation was well above average for the 4 reporting stations during April. Precipitation ranged from 188 to 368 percent of average for the month. The entire basin received 265 percent of average for the month (337 percent of last year). The basin year-to-date precipitation is currently 115 percent of average (137 percent of last year). Year to date percentages range from 106 to 207.

Reservoir
Fontenelle Reservoir is currently storing 134,100 acre feet; this is 83 percent of average (102 % of last year). Flaming Gorge is currently storing 3,140,300 acre feet (at this time last year the reservoir was storing 3,190,600 acre feet). Flaming Gorge has a maximum capacity of 3,749,000 acre feet. Viva Naughton did not report this month.

Streamflow
Expected yields vary from 93 to 119 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 1070,000-acre feet (119 percent of average). East Fork of Smiths Fork near Robertson is estimated to yield 28,000 acre-feet (93 percent of average). The estimated yield for Hams Fork near Frontier is 75,000-acre feet (114 percent of average). Viva Naughton Reservoir inflow will be about 100,000-acre feet (112 percent of average). 

==================================================================================================================================
                                                     LOWER GREEN RIVER BASIN
                                               Streamflow Forecasts - May 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       917       996    |     1070       119    |      1144      1223            899
                                                                    |                       |
Blacks Fork nr Robertson             APR-JUL        74        84    |       90        95    |        96       106             95
                                                                    |                       |
EF of Smiths Fork nr Robertson       APR-JUL        24        26    |       28        93    |        30        33             30
                                                                    |                       |
Hams Fk blw Pole Ck nr Frontier      APR-JUL        60        69    |       75       114    |        81        91             66
                                                                    |                       |
Hams Fk Inflow to Viva Naughton Res  APR-JUL        81        92    |      100       112    |       108       119             89
                                                                    |                       |
Flaming Gorge Reservoir Inflow       APR-JUL      1148      1347    |     1450       121    |      1553      1746           1196
                                                                    |                       |
==================================================================================================================================
                         LOWER GREEN RIVER BASIN                        |                 LOWER GREEN RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 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    134.1    131.6    161.8 |   HAMS FORK RIVER             4       148       125
                                                                        |
FLAMING GORGE                         3749.0   3140.3   3190.6      --- |   BLACKS FORK                 5        92       109
                                                                        |
VIVA NAUGHTON RES                       42.4     29.2     30.5     26.5 |   HENRYS FORK                 3        65       141
                                                                        |
                                                                        |   GREEN above Flaming Gorge  25       125       123
                                                                        |
==================================================================================================================================
 * 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 1999 Basin Outlook Report Contents Page