Snake River Basin (1)
June 2001

Snow
Nearly all snow has melted from the SNOTEL sites in this basin. Only one site has any snow. 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 63 percent of average (52 percent of last year). May percentages range from 22 to 102 percent of average. Water-year-to- date precipitation is 64 percent of normal for the Snake River basin (87 percent of last year at this time). Year-to-date percentages range from 52 to 78 percent of average.

Reservoir.
Current usable storage compared to average for the three reservoirs in the basin is as follows: Grassy Lake —108 percent of average (14,700 acre feet compared to 14,300 last year), Jackson lake — 140 percent of average (758,200 acre feet compared to 843,900 acre feet last year), and Palisades Reservoir — 80 percent of average (842,500 acre feet compared to 2,182,000 acre feet last year).

Streamflow.
Runoff will be much below average. Irrigators relying on direct diversions from streams may have water shortages. The most probable, 50 percent chance June through September runoff yield forecast is as follows. The Snake near Moran is expected to yield 250,000 acre-feet (43 percent of normal). Yield from the Snake River above Palisades Reservoir is estimated to be 950,000 acre-feet (52 percent of normal). Palisades reservoir inflow will be about 1,300,000 acre feet (53 percent of average). The 50 percent chance yield near Heise is expected to be 1,400,000 acre-feet (53 percent of normal). Pacific Creek at Moran is expected to yield about 88,000 acre-feet (46 percent of average). Greys River above Palisades Reservoir is estimated to yield 125,000 acre-feet (52 percent of normal). Salt River near Etna is estimated to have a yield of 100,000 acre-feet (44 percent of normal). 

==================================================================================================================================
                                                        SNAKE RIVER BASIN
                                               Streamflow Forecasts - June 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)               JUN-SEP        94       201    |      250        43    |       299       406            579
                                                                    |                       |
SNAKE above Palisades (2)            JUN-SEP       711       853    |      950        52    |      1047      1189           1823
                                                                    |                       |
PALISADES RESERVOIR INFLOW (1,2)     JUN-SEP       863      1164    |     1300        53    |      1436      1737           2459
                                                                    |                       |
SNAKE near Heise (2)                 JUN-SEP      1023      1248    |     1400        53    |      1552      1777           2622
                                                                    |                       |
PACIFIC CREEK at Moran               JUN-SEP        24        38    |       48        46    |        58        72            104
                                                                    |                       |
GREYS above Palisades                JUN-SEP        87       110    |      125        52    |       140       163            241
                                                                    |                       |
SALT near Etna                       JUN-SEP        54        81    |      100        44    |       119       146            228
                                                                    |                       |
==================================================================================================================================
                            SNAKE RIVER BASIN                           |                    SNAKE RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 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     14.7     14.3     13.6 |   SNAKE above Jackson Lake    5        20         5
                                                                        |
JACKSON LAKE                           847.0    758.2    843.9    540.5 |   PACIFIC CREEK               2        20        12
                                                                        |
PALISADES                             1400.0    842.5   1323.8   1055.0 |   GROS VENTRE RIVER           2         0         0
                                                                        |
                                                                        |   HOBACK RIVER                5         0         0
                                                                        |
                                                                        |   GREYS RIVER                 4         0         0
                                                                        |
                                                                        |   SALT RIVER                  3         0         0
                                                                        |
                                                                        |   SNAKE above Palisades      17         9         2
                                                                        |
==================================================================================================================================
 * 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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