Snake River Basin (1)
January 2000

Snow.
Percentage of average snow water equivalent (SWE) for each drainage in the basin is: Snake above Jackson Lake -- 65 percent (60% of last year at this time), Pacific Creek -- 72 percent (64% of last year at this time), Gros Ventre River -- 47 percent (50% of last year at this time), Hoback River -- 57 percent (61% of last year at this time), Greys River -- 62 percent (67% of last year at this time), Salt River -- 64 percent (66% of last year at this time). Snake River Basin above Palisades is 64 percent of average (61% 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 above average for last month. Monthly precipitation, for the basin, was 63 percent of average (74 percent of last year). December percentages range from 36 to 122 percent of average. Water-year-to-date precipitation is 52 percent of normal for the Snake River basin (55 percent of last year at this time) Year-to-date percentages range from 24 to 62 percent of average.

Reservoir.
Current storage compared to average for the three storage reservoirs in the basin is as follows: Grassy Lake -116 percent of average (12,200 acre feet compared to 12,600 last year), Jackson lake - 134 percent of average (632,300 acre feet compared to 590,000 acre feet last year), and Palisades Reservoir -113 percent of average (1,173,000 acre feet compared to 1,207,300 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 702,000 acre-feet (81 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 2,166,000 acre-feet (81 percent of normal). The 50 percent chance yield near Heise is expected to be 3,170,000 acre-feet (78 percent of normal). Pacific Creek at Moran is expected to yield about 131,000 acre-feet (79 percent of average). Greys River above Palisades Reservoir is estimated to yield 280,000 acre-feet (72 percent of normal). Salt River near Etna is estimated to have a yield of 285,000 acre-feet (71 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - January 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)
====================================================================|=======================|=====================================
SNAKE near Moran (1,2)               APR-SEP       466       628    |      702        81    |       776       938            869
                                                                    |                       |
SNAKE above Palisades (2)            APR-SEP      1593      1934    |     2166        81    |      2398      2739           2671
                                                                    |                       |
SNAKE near Heise (2)                 APR-SEP      2257      2801    |     3170        78    |      3539      4083           4049
                                                                    |                       |
PACIFIC CREEK at Moran               APR-SEP        87       113    |      131        79    |       149       175            166
                                                                    |                       |
GREYS above Palisades                APR-SEP       170       235    |      280        72    |       325       390            388
                                                                    |                       |
SALT near Etna                       APR-SEP       151       231    |      285        71    |       339       419            399
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 2000
==================================================================================================================================
                                      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     12.2     12.6     10.5 |   SNAKE above Jackson Lake    9        60        66
                                                                        |
JACKSON LAKE                           847.0    632.3    590.0    470.2 |   PACIFIC CREEK               3        59        69
                                                                        |
PALISADES                             1400.0   1173.0   1207.3   1036.0 |   GROS VENTRE RIVER           2        50        47
                                                                        |
                                                                        |   HOBACK RIVER                5        61        57
                                                                        |
                                                                        |   GREYS RIVER                 3        66        62
                                                                        |
                                                                        |   SALT RIVER                  3        66        64
                                                                        |
                                                                        |   SNAKE above Palisades      21        61        63
                                                                        |
==================================================================================================================================
 * 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.
(3) - Forecasts produced in cooperation with Alberta Forecasting Staff Canada
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