Powder and Tongue River Basins (6)
May 2001

Snow
Snow water equivalent (SWE) in the Upper Tongue River drainage is 61 percent of normal (73 percent of last year). The Goose Creek drainage is 61 percent of average (78 percent of last year). Clear Creek drainage is 47 percent of normal SWE (82 percent of last year). Crazy Woman Creek is 69 percent of average (109 percent of last year). The Upper Powder River drainage is 47 percent of average (80 percent of last year). The Powder River basin snow water equivalent (SWE), in Wyoming, is about 47 percent of average (81 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
April precipitation was 85 percent of average for the 11 reporting stations (85 percent of last year). Monthly percentages range from 47 to 137 percent of average. Precipitation for the year ranges from 59 to 83 percent of average at the reporting stations. Year-to-date precipitation is about 73 percent of average in the basin; this is 78 percent of last year at this time.

Reservoir
Tongue River Reservoir is currently at 122 percent of average usable storage for this time of year (44,500 acre feet) - the reservoir is about 46 percent of capacity (total capacity is 79,100 acre feet). Last year at this time the reservoir was storing about 41,100 acre feet - average storage is about 36,600 acre feet for this time of the year. 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 65,000-acre feet (60 percent of normal). Middle Fork of the Powder River near Barnum is estimated to yield 5,700-acre feet (32 percent of average). The North Fork of the Powder near Hazelton should yield about 5,300 acre-feet (56 percent of normal). The estimated yield for Clear Creek near Buffalo is 19,000 acre-feet (51 percent of average). Rock Creek near Buffalo will yield about 11,000 acre-feet (48 percent of normal), and Piney Creek at Kearny should yield about 19,500 acre-feet (42 percent of average). 

==================================================================================================================================
                                                   POWDER & TONGUE RIVER BASINS
                                               Streamflow Forecasts - May 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)
====================================================================|=======================|=====================================
TONGUE RIVER nr Dayton (2)           MAY-SEP        50        59    |       65        60    |        75        89            109
                                                                    |                       |
MIDDLE FORK POWDER nr Barnum         MAY-SEP       3.9       5.0    |      5.7        32    |       7.9      11.3           17.7
                                                                    |                       |
NORTH FORK POWDER nr Hazelton        MAY-SEP      3.90      4.73    |     5.30        56    |      6.31      7.80           9.50
                                                                    |                       |
CLEAR CREEK nr Buffalo               MAY-SEP      15.4      17.5    |     19.0        51    |        22        26             37
                                                                    |                       |
ROCK CREEK nr Buffalo                MAY-SEP       8.4       9.9    |     11.0        48    |      13.2      16.4             23
                                                                    |                       |
PINEY CREEK at Kearny                MAY-SEP       9.3      15.4    |     19.5        42    |        29        44             47
                                                                    |                       |
==================================================================================================================================
                      POWDER & TONGUE RIVER BASINS                      |              POWDER & TONGUE RIVER BASINS
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 2001
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
TONGUE RIVER                            79.1     44.5     41.1     36.6 |   UPPER TONGUE RIVER          8        74        61
                                                                        |
                                                                        |   GOOSE CREEK                 2        76        61
                                                                        |
                                                                        |   CLEAR CREEK                 4        82        47
                                                                        |
                                                                        |   CRAZY WOMAN CREEK           3       109        69
                                                                        |
                                                                        |   UPPER POWDER RIVER          4        80        47
                                                                        |
                                                                        |   POWDER RIVER in WY          8        81        47
                                                                        |
==================================================================================================================================
 * 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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