Snake River Basin (1)
February 2000

Snow
Percentage of average snow water equivalent (SWE) for each drainage in the basin is: Snake above Jackson Lake -- 75 percent (65% of last year at this time), Pacific Creek -- 84 percent (68% of last year at this time), Gros Ventre River -- 71 percent (70% of last year at this time), Hoback River -- 79 percent (83% of last year at this time), Greys River -- 87 percent (92% of last year at this time), Salt River -- 88 percent (92% of last year at this time). Snake River Basin above Palisades is 79 percent of average (73% 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 101 percent of average (98 percent of last year). January percentages range from 75 to 181 percent of average. Water-year-to-date precipitation is 66 percent of normal for the Snake River basin (70 percent of last year at this time) Year-to-date percentages range from 43 to 80 percent of average.

Reservoir.
Current storage compared to average for the three storage reservoirs in the basin is as follows: Grassy Lake -115 percent of average (12,400 acre feet compared to 12,900 last year), Jackson lake - 134 percent of average (645,000 acre feet compared to 606,000 acre feet last year), and Palisades Reservoir -118 percent of average (1,232,200 acre feet compared to 1,196,000 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 710,000 acre-feet (82 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 2,138,000 acre-feet (80 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 130,000 acre-feet (78 percent of average). Greys River above Palisades Reservoir is estimated to yield 295,000 acre-feet (76 percent of normal). Salt River near Etna is estimated to have a yield of 310,000 acre-feet (78 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - February 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       519       650    |      710        82    |       770       901            869
                                                                    |                       |
SNAKE above Palisades (2)            APR-SEP      1703      1962    |     2138        80    |      2314      2573           2671
                                                                    |                       |
SNAKE near Heise (2)                 APR-SEP      2419      2866    |     3170        78    |      3474      3921           4049
                                                                    |                       |
PACIFIC CREEK at Moran               APR-SEP        96       116    |      130        78    |       144       164            166
                                                                    |                       |
GREYS above Palisades                APR-SEP       209       260    |      295        76    |       330       381            388
                                                                    |                       |
SALT near Etna                       APR-SEP       196       264    |      310        78    |       356       424            399
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of January               |        Watershed Snowpack Analysis - February 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     12.4     12.9     10.8 |   SNAKE above Jackson Lake    9        65        76
                                                                        |
JACKSON LAKE                           847.0    645.0    606.9    479.6 |   PACIFIC CREEK               3        67        83
                                                                        |
PALISADES                             1400.0   1232.2   1196.0   1044.0 |   GROS VENTRE RIVER           3        67        69
                                                                        |
                                                                        |   HOBACK RIVER                6        83        79
                                                                        |
                                                                        |   GREYS RIVER                 4        92        86
                                                                        |
                                                                        |   SALT RIVER                  5        92        88
                                                                        |
                                                                        |   SNAKE above Palisades      30        74        80
                                                                        |
==================================================================================================================================
 * 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 February 2000 Basin Outlook Report Contents Page