Bighorn River Basin (4)
April 1998

Snow
The Nowood drainage SWE is 72 percent of last year and 86 percent of April one average. Greybull River drainage SWE is 131 percent of average (97 percent of last year). Shell Creek SWE is about 91 percent of average (80 percent of last year). The basin SWE, as a whole, is currently 94 percent of average (80 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
March precipitation was 95 percent of the monthly average (119 percent of last year). Black Mountain was the station reporting the highest percentage of average for March (196 percent of average). Burgess Junction-SCS had the lowest percentage of average (55 percent). Year-to-date precipitation is 104 percent of normal; that is 91 percent of last year at this time.

Reservoir
Boysen Reservoir is currently storing 509,800 acre feet (96 percent of average). Bighorn Lake is now at 108 percent of average (860,400 acre feet). Boysen is currently storing 112 percent of last year at this time and Big Horn Lake is storing 113 percent of last year's volume.

Streamflow
The 50 percent chance April through September runoff is anticipated to be normal or below. The Wind River below Boysen is forecast to yield 755,000 acre feet (93 percent of average); the Nowood River near Ten Sleep should yield near 54,000 acre feet (93 percent of normal); the Greybull River at Meeteese should yield 200,000 acre feet (average); Shell Creek near Shell should yield 70,000 acre feet (93 percent of average) and the Bighorn River at Kane should yield 1,070,000 acre feet (95 percent of average). 

==================================================================================================================================
                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - April 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)
====================================================================|=======================|=====================================
WIND RIVER below Boysen (2)          APR-SEP       459       635    |      755        93    |       875      1051            809
                                                                    |                       |
NOWOOD RIVER near Tensleep           APR-SEP        22        41    |       54        93    |        67        86             58
                                                                    |                       |
GREYBULL RIVER at Meeteetse          APR-SEP       158       183    |      200       100    |       217       242            201
                                                                    |                       |
SHELL CREEK near Shell               APR-SEP        58        65    |       70        93    |        75        82             75
                                                                    |                       |
BIGHORN RIVER at Kane (2)            APR-SEP       697       901    |     1070        95    |      1239      1450           1124
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 1998
==================================================================================================================================
                                      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    509.8    456.2    529.3 |   NOWOOD RIVER                5        72        86
                                                                        |
BIGHORN LAKE                          1356.0    860.4    761.0    798.5 |   GREYBULL RIVER              2        97       131
                                                                        |
                                                                        |   SHELL CREEK                 4        80        91
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)   11        80        94
                                                                        |
==================================================================================================================================
 * 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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