Bighorn River Basin (4)
April 1999

Snow
Snowpack in this basin is near average, except for the Greybull River drainage, which is 11 percent above average. The Nowood drainage is 90 percent (104 percent of last year). The Greybull River drainage SWE is 111 percent of average (85 percent of last year). Shell Creek SWE is 102 percent of average (112 percent of last year). The basin SWE, as a whole, is currently 98 percent of average (104 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
March precipitation was 65 percent of the monthly average (62 percent of last year). Sites ranged from 0 percent to 103 percent of average for the month. Year-to-date precipitation is 115 percent of normal; that is 108 percent of last year at this time. Year to date percentages, from the 15 reporting stations, range from 85 to 144.

Reservoir
Boysen Reservoir is currently storing 473,800-acre feet (90 percent of average). Bighorn Lake is now at 98 percent of average (782,600-acre feet). Boysen is currently storing 93 percent of last year at this time and Big Horn Lake is storing 91 percent of last year's volume.

Streamflow
The 50 percent chance April through September runoff is anticipated to be near normal. The Wind River at Boysen is forecast to yield 940,000 acre feet (116 percent of average); the Nowood River near Ten Sleep should yield near 60,000 acre feet (103 percent of normal); the Greybull River at Meeteese should yield 210,000 acre feet (105 percent of average); Shell Creek near Shell should yield 70,000 acre feet (93 percent of average) and the Bighorn River at Kane should yield 1,230,000 acre feet (109 percent of average). 

==================================================================================================================================
                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - April 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)
====================================================================|=======================|=====================================
BOYSEN Reservoir Inflow (2)          APR-SEP       644       820    |      940       116    |      1060      1236            809
                                                                    |                       |
NOWOOD RIVER nr Tensleep (D)         APR-SEP        31        48    |       60       103    |        72        89             58
                                                                    |                       |
GREYBULL RIVER nr Meeteetse          APR-SEP       169       194    |      210       105    |       226       251            201
                                                                    |                       |
SHELL CREEK nr Shell                 APR-SEP        59        66    |       70        93    |        74        81             75
                                                                    |                       |
BIGHORN RIVER at Kane (2)            APR-SEP       812      1061    |     1230       109    |      1399      1648           1124
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 1999
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
BOYSEN                                 596.0    473.8    509.8    529.3 |   NOWOOD RIVER                5       104        90
                                                                        |
BIGHORN LAKE                          1356.0    782.6    860.4    798.5 |   GREYBULL RIVER              2        85       111
                                                                        |
                                                                        |   SHELL CREEK                 4       112       102
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)   11       104        98
                                                                        |
==================================================================================================================================
 * 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.
(D) - The operational measurement of flow at this point has been discountinued.
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