Powder and Tongue River Basins (6)
May 1998

Snow
The Powder River basin snow water equivalent (SWE), in Wyoming, is now 95 percent of average (78 percent of last year at this time). The Upper Tongue River drainage is 95 percent of normal (83 percent of last year). Goose Creek drainage is 95 percent of normal (86 percent of last year). Clear Creek drainage is 100 percent of normal (90 percent of last year). Crazy Woman Drainage is 113 percent of normal (75 percent of last year), and the Upper Powder is 92 percent of average (69 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
April precipitation was 129 percent of average for the 12 reporting stations (118 percent of last year). Precipitation for the year ranges from 72 percent of average at Hecla to 152 percent of average at Billy Creek. Year-to-date precipitation is 107 percent of average in the basin; this is 97 percent of last year at this time.

Reservoir
Storage in the Tongue River Reservoir this month is 10,000 acre feet (27 percent of average). Normally, Tongue River reservoir stores 36,600 acre feet of water (52 percent of capacity).

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 110,000 acre feet (101 percent of normal). Water users on the Middle Fork near Barnum should have a yield near 16,000 acre feet (90 percent of normal). The North Fork of the Powder near Hazelton should yield about 8,600 acre feet (91 percent of normal). The estimated yield for Clear Creek near Buffalo is 38,000 acre feet (103 percent of average). Rock Creek near Buffalo will yield about 22,000 acre feet (94 percent of normal), and Piney Creek at Kearny should yield about 48,000 acre feet (102 percent of average). 


==================================================================================================================================
                                                   POWDER & TONGUE RIVER BASINS
                                               Streamflow Forecasts - May 1, 1998
==================================================================================================================================
                                              |  <<====== 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        87       101    |      110       101    |       119       133            109
                                                                    |                       |
MIDDLE FORK POWDER near Barnum       MAY-SEP      10.4      13.7    |     16.0        90    |      18.3        22           17.7
                                                                    |                       |
NORTH FORK POWDER near Hazelton      MAY-SEP      6.29      7.67    |     8.60        91    |      9.53     10.91           9.50
                                                                    |                       |
CLEAR CREEK near Buffalo             MAY-SEP        30        35    |       38       103    |        41        46             37
                                                                    |                       |
ROCK CREEK near Buffalo              MAY-SEP      17.2      19.8    |       22        94    |        23        26             23
                                                                    |                       |
PINEY CREEK at Kearny                MAY-SEP        32        42    |       48       102    |        55        64             47
                                                                    |                       |
==================================================================================================================================
                      POWDER & TONGUE RIVER BASINS                      |              POWDER & TONGUE RIVER BASINS
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 1, 1998
==================================================================================================================================
                                      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     10.0     18.0     36.6 |   UPPER TONGUE RIVER          9        83        95
                                                                        |
                                                                        |   GOOSE CREEK                 3        86        95
                                                                        |
                                                                        |   CLEAR CREEK                 4       123       123
                                                                        |
                                                                        |   CRAZY WOMAN CREEK           3       102       136
                                                                        |
                                                                        |   UPPER POWDER RIVER          4        73       101
                                                                        |
                                                                        |   POWDER RIVER in WY          8        94       112
                                                                        |
==================================================================================================================================
 * 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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