Snake River Basin
January 1997

Snow
Snowfall has been well above average in the basin this year. Percent of average snow water equivalent (SWE) for each drainage in the basin is: Snake above Jackson - 209% (70% above last year), Pacific Creek - 215% (57% above last year), Gros Ventre River - 189% (33% above last year), Hoback River -18% (53% above last year), Greys River - 197% (44% above last year), Salt River - 205% (42% above last year), Snake above Palisades - 210% (60% above last year. See the Basin Summary of Snow Courses at the beginning of this report for a detailed listing of snow course information.

Precipitation.
Precipitation across the basin was much above average last month. Togwotee Pass was the lowest reporting site with 197 percent of average for December. December precipitation for the basin was 249 percent of average. Water year to date precipitation is 66 percent above normal for the Snake River basin. Year-to-date precipitation is 37 percent ahead of last year.

Reservoir.
Current storage compared to average for the three storage reservoirs in the basin is as follows; Grassy Lake 121% (12,700 acre feet), Jackson lake 145% (680,000 acre feet), and Palisades Reservoir 120% (1,244,900 acre feet). Grassy Lake is about 1 percent below last years storage amount, while Jackson Lake is 2 percent more and Palisades Reservoir is 10 percent less than last year at this time.

Streamflow.
Stream flow is forecast to be much above average for the basin. The 50 percent chance yields for the April to September period are forecast to be 36 to 51 percent above normal in the Snake River basin. The 50 percent chance yield from the Snake River above Palisades Reservoir is estimated to be 3,727,000 acre feet; this is 41 percent more than normal. The Snake at Moran is expected to yield 1,180,000 acre feet (36 percent above normal). Pacific Creek at Moran will probably yield 260,000 acre feet (51 percent more than average). Greys River near Palisades Reservoir is estimated to yield 565,000 acre feet (46 percent more than normal). Salt River near Etna is estimated to have a yield of 595,000 acre feet (49 percent above normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - January 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)
====================================================================|=======================|=====================================
SNAKE nr Moran (1,2)                 APR-SEP       897      1092    |     1180       136    |      1268      1463            869
                                                                    |                       |
SNAKE R abv Palisades Rsvr nr Alpine APR-SEP      3088      3468    |     3727       141    |      3986      4366           2647
                                                                    |                       |
SNAKE nr Heise (2)                   APR-SEP      4614      5261    |     5700       141    |      6139      6786           4048
                                                                    |                       |
PACIFIC CREEK at Moran               APR-SEP       208       239    |      260       151    |       281       312            172
                                                                    |                       |
GREYS R abv Palisades Reservoir      APR-SEP       454       520    |      565       146    |       610       676            388
                                                                    |                       |
SALT abv Reservoir nr Etna           APR-SEP       450       536    |      595       149    |       654       740            400
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 1997
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
GRASSY LAKE                             15.2     12.7     12.8     10.5 |   SNAKE above Jackson Lake   10       170       209
                                                                        |
JACKSON LAKE                           847.0    680.0    667.8    470.2 |   PACIFIC CREEK               3       157       215
                                                                        |
PALISADES                             1400.0   1244.9   1375.9   1035.6 |   GROS VENTRE RIVER           2       133       189
                                                                        |
                                                                        |   HOBACK RIVER                5       153       218
                                                                        |
                                                                        |   GREYS RIVER                 2       144       197
                                                                        |
                                                                        |   SALT RIVER                  4       142       205
                                                                        |
                                                                        |   SNAKE above Palisades      22       160       210
                                                                        |
==================================================================================================================================
 * 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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