Snake River Basin (1)
January 2001

Snow
Percentage of average snow water equivalent (SWE) for each drainage in the basin is: Snake above Jackson Lake -- 71 percent (107% of last year at this time), Pacific Creek -- 78 percent (111% of last year at this time), Gros Ventre River -- 80 percent (159% of last year at this time), Hoback River -- 80 percent (139% of last year at this time), Greys River -- 81 percent (128% of last year at this time), Salt River -- 89 percent (137% of last year at this time). Snake River Basin above Palisades is 77 percent of average (123% 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 below average for last month. Monthly precipitation, for the basin, was 74 percent of average (101 percent of last year). December percentages range from 4 to 96 percent of average. Water- year-to-date precipitation is 74 percent of normal for the Snake River basin (144 percent of last year at this time) Year-to-date percentages range from 61 to 96 percent of average.

Reservoir.
Current storage compared to average for the three storage reservoirs in the basin is as follows: Grassy Lake -120 percent of average (12,600 acre feet compared to 12,200 last year), Jackson lake - 136 percent of average (637,600 acre feet compared to 632,300 acre feet last year), and Palisades Reservoir -56 percent of average (575,000 acre feet compared to 1,173,000 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 755,000 acre-feet (87 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 2,402,000 acre-feet (90 percent of normal). The 50 percent chance yield near Heise is expected to be 3,530,000 acre-feet (87 percent of normal). Pacific Creek at Moran is expected to yield about 150,000 acre-feet (90 percent of average). Greys River above Palisades Reservoir is estimated to yield 340,000 acre-feet (88 percent of normal). Salt River near Etna is estimated to have a yield of 345,000 acre-feet (87 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - January 1, 2001
==================================================================================================================================
                                              |  <<====== 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       519       681    |      755        87    |       829       991            869
                                                                    |                       |
SNAKE above Palisades (2)            APR-SEP      1829      2170    |     2402        90    |      2634      2975           2671
                                                                    |                       |
SNAKE near Heise (2)                 APR-SEP      2617      3161    |     3530        87    |      3899      4443           4049
                                                                    |                       |
PACIFIC CREEK at Moran               APR-SEP       106       132    |      150        90    |       168       194            166
                                                                    |                       |
GREYS above Palisades                APR-SEP       230       295    |      340        88    |       385       450            388
                                                                    |                       |
SALT near Etna                       APR-SEP       211       291    |      345        87    |       399       479            399
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 2001
==================================================================================================================================
                                      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     12.6     12.2     10.5 |   SNAKE above Jackson Lake    9       107        71
                                                                        |
JACKSON LAKE                           847.0    637.6    632.3    470.2 |   PACIFIC CREEK               3       111        78
                                                                        |
PALISADES                             1400.0    575.0   1173.0   1036.0 |   GROS VENTRE RIVER           2       159        80
                                                                        |
                                                                        |   HOBACK RIVER                5       139        80
                                                                        |
                                                                        |   GREYS RIVER                 4       128        81
                                                                        |
                                                                        |   SALT RIVER                  3       137        89
                                                                        |
                                                                        |   SNAKE above Palisades      21       123        77
                                                                        |
==================================================================================================================================
 * 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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