Powder and Tongue River Basins (6)
May 1999

Snow
The Powder River basin snow water equivalent (SWE), in Wyoming, is now 106 percent of average (95 percent of last year at this time). The Upper Tongue River drainage is 98 percent of normal (102 percent of last year). Goose Creek drainage is 93 percent of average (97 percent of last year). Clear Creek drainage is 105 percent of normal (84 percent of last year). Crazy Woman Drainage is 127 percent of normal (93 percent of last year). The Upper Powder River is 108 percent of normal (108 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
April precipitation was 189 percent of average for the 11 reporting stations (142 percent of last year). Monthly percentages range from 115 to 275 percent of average. Precipitation for the year ranges from 99 to 161 percent of average. Year-to-date precipitation is 126 percent of average in the basin; this is 117 percent of last year at this time.

Reservoir
Tongue River Reservoir is currently at 75 percent of average (273 percent of last year), and 40 percent of the total capacity). About 27,300 acre feet are presently being stored, compared to 10,000 acre feet last year. The total reservoir capacity is about 68,000 acre feet Detailed reservoir data is shown on the following page and on the reservoir storage summary at the beginning of this report.

Streamflow
The following runoff values are for the 50 percent probability during the May through September forecast period. The estimated yield for Tongue River near Dayton is 96,000 acre-feet (88 percent of normal). Water users on the Middle Fork near Barnum should have a yield near 15,900 acre-feet (90 percent of normal). The North Fork of the Powder near Hazelton should yield about 10,500 acre-feet (111 percent of normal). The estimated yield for Clear Creek near Buffalo is 36,000 acre-feet (97 percent of average). Rock Creek near Buffalo will yield about 24,500 acre-feet (107 percent of normal), and Piney Creek at Kearny should yield about 48,500 acre-feet (103 percent of average). 

==================================================================================================================================
                                                   POWDER & TONGUE RIVER BASINS
                                               Streamflow Forecasts - May 1, 1999
==================================================================================================================================
                                              |  <<====== 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 nr Dayton (2)           MAY-SEP        72        86    |       96        88    |       106       120            109
                                                                    |                       |
MIDDLE FORK POWDER nr Barnum         MAY-SEP      10.3      13.7    |     15.9        90    |      18.1        22           17.7
                                                                    |                       |
NORTH FORK POWDER nr Hazelton        MAY-SEP      8.00      9.49    |    10.50       111    |     11.51     13.00           9.50
                                                                    |                       |
CLEAR CREEK nr Buffalo               MAY-SEP        29        33    |       36        97    |        39        43             37
                                                                    |                       |
ROCK CREEK nr Buffalo                MAY-SEP      19.1        22    |       25       107    |        27        30             23
                                                                    |                       |
PINEY CREEK at Kearny                MAY-SEP        24        39    |       49       103    |        58        73             47
                                                                    |                       |
==================================================================================================================================
                      POWDER & TONGUE RIVER BASINS                      |              POWDER & TONGUE RIVER BASINS
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1999
==================================================================================================================================
                                      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     27.3     10.0     36.6 |   UPPER TONGUE RIVER          9       102        98
                                                                        |
                                                                        |   GOOSE CREEK                 3        97        93
                                                                        |
                                                                        |   CLEAR CREEK                 4        84       105
                                                                        |
                                                                        |   CRAZY WOMAN CREEK           3        93       127
                                                                        |
                                                                        |   UPPER POWDER RIVER          4       108       108
                                                                        |
                                                                        |   POWDER RIVER in WY          8        95       106
                                                                        |
==================================================================================================================================
 * 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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