Snake River Basin (1)
January 2002

Snow
The Snake River basin snow water equivalent (SWE) is below normal. Snake above Jackson Lake is 82 percent (124% of last year at this time). Pacific Creek is 78 percent of average (116% of last year at this time). Gros Ventre River is 91 percent of average (123% of last year at this time). Hoback River is 90 percent of average (119% of last year at this time), Greys River is 86 percent of average (116% of last year at this time). Salt River is 81 percent of average (100% of last year at this time). Snake River Basin above Palisades is 85 percent of average (119% of last year at this time). 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 near average last month. Monthly precipitation, for the basin, was 99 percent of average (125 percent of last year). Last months percentages range from 84 to 153 percent of average. Water-year-to- date precipitation is 94 percent of normal for the Snake River basin (121 percent of last year at this time) Year-to-date percentages range from 83 to 114 percent of average.

Reservoir.
Current reservoir storage compared to average for the three storage reservoirs in the basin is below average. Grassy Lake storage is about 79 percent of average (9,200 acre feet compared to 12,600 last year). Jackson Lake storage is 29 percent of average (137,400 acre feet compared to 637,300 acre feet last year). Palisades Reservoir storage is about 42 percent of average (439,000 acre feet compared to 1,225,000 acre feet last year).

Streamflow.
The most probable, 50 percent chance, April through September runoff yield forecast is below average for the basin. The Snake near Moran is expected to yield 750,000 acre-feet (83 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 2,305,000 acre-feet (84 percent of normal). The 50 percent chance yield near Heise is expected to be 3,510,000 acre-feet (84 percent of normal). Pacific Creek at Moran is expected to yield about 137,000 acre-feet (77 percent of average). Greys River above Palisades Reservoir is estimated to yield 355,000 acre- feet (90 percent of normal). Salt River near Etna is estimated to have a yield of 360,000 acre-feet (86 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - January 1, 2002
==================================================================================================================================
                                              |  <<====== 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 near Moran (1,2)               APR-SEP       514       676    |      750        83    |       824       986            905
                                                                    |                       |
SNAKE above Palisades (2)            APR-SEP      1732      2073    |     2305        84    |      2537      2878           2730
                                                                    |                       |
PALISADES RESERVOIR INFLOW (1,2)     APR-SEP      2212      2953    |     3290        85    |      3627      4368           3870
                                                                    |                       |
SNAKE near Heise (2)                 APR-SEP      2597      3141    |     3510        84    |      3879      4423           4160
                                                                    |                       |
PACIFIC CREEK at Moran               APR-SEP        93       119    |      137        77    |       155       181            178
                                                                    |                       |
GREYS above Palisades                APR-SEP       245       310    |      355        90    |       400       465            395
                                                                    |                       |
SALT near Etna                       APR-SEP       226       306    |      360        86    |       414       494            420
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 2002
==================================================================================================================================
                                      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      9.2     12.6     11.6 |   SNAKE above Jackson Lake    9       123        83
                                                                        |
JACKSON LAKE                           847.0    137.4    637.6    481.7 |   PACIFIC CREEK               3       117        86
                                                                        |
PALISADES                             1400.0    439.3    575.0   1036.5 |   GROS VENTRE RIVER           2       123        91
                                                                        |
                                                                        |   HOBACK RIVER                5       119        90
                                                                        |
                                                                        |   GREYS RIVER                 4       116        86
                                                                        |
                                                                        |   SALT RIVER                  3       100        81
                                                                        |
                                                                        |   SNAKE above Palisades      21       119        86
                                                                        |
==================================================================================================================================
 * 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 1971-2000 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 January 2002 Basin Outlook Report Contents Page