Snake River Basin (1)
February 2001

Snow
Percentage of average snow water equivalent (SWE) for each drainage in the basin is: Snake above Jackson Lake -- 51 percent (66% of last year at this time), Pacific Creek -- 56 percent (67% of last year at this time), Gros Ventre River -- 56 percent (81% of last year at this time), Hoback River -- 57 percent (72% of last year at this time), Greys River - 58 percent (66% of last year at this time), Salt River -- 62 percent (70% of last year at this time). Snake River Basin above Palisades is 55 percent of average (69% 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 much below average for last month. Monthly precipitation, for the basin, was 18 percent of average (18 percent of last year). January percentages range from 8 to 106 percent of average. Water-year-to-date precipitation is 55 percent of normal for the Snake River basin (83 percent of last year at this time) Year-to-date percentages range from 45 to 78 percent of average.

Reservoir
Current storage compared to average for the three storage reservoirs in the basin is as follows: Grassy Lake -118 percent of average (12,700 acre feet compared to 12,400 last year), Jackson lake - 132 percent of average (635,200 acre feet compared to 645,000 acre feet last year), and Palisades Reservoir -61 percent of average (638,700 acre feet compared to 1,232,200 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 595,000 acre-feet (69 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 1,790,000 acre-feet (67 percent of normal). The 50 percent chance yield near Heise is expected to be 2,610,000 acre-feet (65 percent of normal). Pacific Creek at Moran is expected to yield about 106,000 acre-feet (64 percent of average). Greys River above Palisades Reservoir is estimated to yield 255,000 acre-feet (66 percent of normal). Salt River near Etna is estimated to have a yield of 260,000 acre-feet (65 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - February 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       404       535    |      595        69    |       655       786            869
                                                                    |                       |
SNAKE above Palisades (2)            APR-SEP      1355      1614    |     1790        67    |      1966      2225           2671
                                                                    |                       |
SNAKE near Heise (2)                 APR-SEP      1859      2306    |     2610        65    |      2914      3361           4049
                                                                    |                       |
PACIFIC CREEK at Moran               APR-SEP        72        92    |      106        64    |       120       140            166
                                                                    |                       |
GREYS above Palisades                APR-SEP       169       220    |      255        66    |       290       341            388
                                                                    |                       |
SALT near Etna                       APR-SEP       146       214    |      260        65    |       306       374            399
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of January               |        Watershed Snowpack Analysis - February 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     12.7     12.4     10.8 |   SNAKE above Jackson Lake    9        66        51
                                                                        |
JACKSON LAKE                           847.0    635.2    645.0    479.6 |   PACIFIC CREEK               3        67        56
                                                                        |
PALISADES                             1400.0    638.7   1232.2   1044.0 |   GROS VENTRE RIVER           3        83        56
                                                                        |
                                                                        |   HOBACK RIVER                6        72        57
                                                                        |
                                                                        |   GREYS RIVER                 5        66        58
                                                                        |
                                                                        |   SALT RIVER                  5        70        62
                                                                        |
                                                                        |   SNAKE above Palisades      29        69        55
                                                                        |
==================================================================================================================================
 * 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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