Powder and Tongue River Basins
May 1997

Snow
The basin is in good shape as far as snowpack is concerned. All drainage's within the Powder and Tongue River basin are average or above. The entire basin, in Wyoming, is now 123 percent of average Snow Water Equivalent (SWE). The upper Tongue River drainage is about 15 percent above normal; the Goose Creek drainage is about 11 percent ahead of normal; the Clear Creek drainage is 2 percent above normal; the Crazy Woman Drainage is 31 percent above normal. The Upper Powder is 35 percent above normal. For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
Year-to-date precipitation is 12 percent above average in the basin; this is 3 percent less than it was last year at this time. April precipitation was 9 percent above average (84 percent of last year). Precipitation for the year ranges from 69 to 127 percent of average.

Reservoir
Storage in the Tongue River Reservoir this month is 18,000 acre feet (49 percent of average).

Streamflow
The following values are for the 50 percent probability during the May through September forecast period. The Tongue River near Dayton is estimated to yield 115,000 acre feet (6 percent above normal). Water users on the Middle Fork near Barnum should have a yield near 17,700 acre feet (100 percent of normal). The North Fork of the Powder near Hazelton should yield about 11,200 acre feet (18 percent above normal). Clear Creek near Buffalo is estimated to yield 37,000 acre feet (100 percent above average). Rock Creek near Buffalo will yield about 23,000 acre feet (100 percent of normal) and Piney Creek at Kearny should yield about 50,000 acre feet (106 percent above average).

==================================================================================================================================
                                                   POWDER & TONGUE RIVER BASINS
                                               Streamflow Forecasts - May 1, 1997
==================================================================================================================================
                                              |  <<====== 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)
====================================================================|=======================|=====================================
TONGUE RIVER near Dayton (2)         MAY-SEP        92       106    |      115       106    |       124       138            109
                                                                    |                       |
MIDDLE FORK POWDER near Barnum       MAY-SEP      12.1      15.4    |     17.7       100    |        20        23           17.7
                                                                    |                       |
NORTH FORK POWDER near Hazelton      MAY-SEP      8.89     10.27    |    11.20       118    |     12.13     13.51           9.50
                                                                    |                       |
CLEAR CREEK near Buffalo             MAY-SEP        29        34    |       37       100    |        40        45             37
                                                                    |                       |
ROCK CREEK near Buffalo              MAY-SEP      18.7        21    |       23       100    |        25        27             23
                                                                    |                       |
PINEY CREEK at Kearny                MAY-SEP        34        44    |       50       106    |        57        66             47
                                                                    |                       |
==================================================================================================================================
                      POWDER & TONGUE RIVER BASINS                      |              POWDER & TONGUE RIVER BASINS
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1997
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
TONGUE RIVER                            68.0     18.0     27.4     36.6 |   UPPER TONGUE RIVER          9       104       115
                                                                        |
                                                                        |   GOOSE CREEK                 3       107       111
                                                                        |
                                                                        |   CLEAR CREEK                 3        90       102
                                                                        |
                                                                        |   CRAZY WOMAN CREEK           3        93       131
                                                                        |
                                                                        |   UPPER POWDER RIVER          5       111       135
                                                                        |
                                                                        |   POWDER RIVER in WY          8       104       123
                                                                        |
==================================================================================================================================
 * 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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