Snake River Basin
June 2000

Snow
Percentage of average snow water equivalent (SWE) for each drainage in the basin is: Snake above Jackson Lake -- 25 percent (15% of last year at this time), Pacific Creek -- 60 percent (39% of last year at this time), Gros Ventre River -- 45 percent (35% of last year at this time), Hoback River -- 20 percent (11% of last year at this time), Greys River -- 10 percent (8% of last year at this time), Salt River -- 0 percent (0% of last year at this time). Snake River Basin above Palisades is 20 percent of average (14% 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 118 percent of average (101 percent of last year). May percentages range from 81 to 176 percent of average. Water-year-to-date precipitation is 80 percent of normal for the Snake River basin (75 percent of last year at this time) Year-to-date percentages range from 67 to 90 percent of average.

Reservoir.
Current storage compared to average for the three storage reservoirs in the basin is as follows: Grassy Lake -105 percent of average (14,300 acre feet compared to 13,600 last year), Jackson lake - 156 percent of average (843,900 acre feet compared to 646,000 acre feet last year), and Palisades Reservoir -125 percent of average (1,323,800 acre feet compared to 723,300 acre feet last year).

Streamflow
The most probable, 50 percent chance, June through September runoff yield forecast is below average for the basin. The Snake near Moran is expected to yield 418,000 acre-feet (72 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 1,565,000 acre-feet (86 percent of normal). The 50 percent chance yield near Heise is expected to be 2,140,000 acre-feet (82 percent of normal). Pacific Creek at Moran is expected to yield about 85,000 acre-feet (82 percent of average). Greys River above Palisades Reservoir is estimated to yield 149,000 acre-feet (62 percent of normal). Salt River near Etna is estimated to have a yield of 121,000 acre-feet (53 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - June 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)               JUN-SEP       262       369    |      418        72    |       467       574            579
                                                                    |                       |
SNAKE above Palisades (2)            JUN-SEP      1326      1468    |     1565        86    |      1662      1804           1823
                                                                    |                       |
SNAKE near Heise (2)                 JUN-SEP      1763      1988    |     2140        82    |      2292      2517           2622
                                                                    |                       |
PACIFIC CREEK at Moran               JUN-SEP        61        75    |       85        82    |        95       109            104
                                                                    |                       |
GREYS above Palisades                JUN-SEP       111       134    |      149        62    |       164       187            241
                                                                    |                       |
SALT near Etna                       JUN-SEP        75       102    |      121        53    |       140       167            228
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 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     14.3     13.6     13.6 |   SNAKE above Jackson Lake    5        15        25
                                                                        |
JACKSON LAKE                           847.0    843.9    646.0    540.5 |   PACIFIC CREEK               2        39        60
                                                                        |
PALISADES                             1400.0   1323.8    723.3   1055.0 |   GROS VENTRE RIVER           2        25        45
                                                                        |
                                                                        |   HOBACK RIVER                5        11        20
                                                                        |
                                                                        |   GREYS RIVER                 4         8        10
                                                                        |
                                                                        |   SALT RIVER                  3         0         0
                                                                        |
                                                                        |   SNAKE above Palisades      17        13        20
                                                                        |
==================================================================================================================================
 * 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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