Bighorn River Basin (13)
April 2001

Snow
Snowpack in this basin is well below average for this time of year. The Nowood drainage SWE is 58 percent of average (65 percent of last year). Greybull River SWE is 53 percent of average (75 percent of last year). Shell Creek SWE is 66 percent of average (70 percent of last year). The basin SWE, as a whole, is currently 61 percent of average (69 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
March precipitation was 71 percent of the monthly average (87 percent of last year). Sites ranged from 23 to 113 percent of average for the month. Year-to-date precipitation is 69 percent of normal; that is 78 percent of last year at this time. Year to date percentages, from the 13 reporting stations, range from 56 to 161.

Reservoir
Usable storage in Boysen Reservoir is currently 447,200-acre feet (84 percent of average). Bighorn Lake is now at 107 percent of average (854,300-acre feet). Boysen is currently storing 85 percent of last year at this time and Big Horn Lake is storing 94 percent of last year's volume.

Streamflow
The 50 percent chance April through September runoff is anticipated to be below normal. The Boysen Reservoir inflow is forecast to yield 320,000 acre feet (40 percent of average); the Greybull River nr Meeteese should yield 90,000 acre feet (45 percent of average); Shell Creek near Shell should yield 42,000 acre feet (56 percent of average) and the Bighorn River at Kane should yield 230,000 acre feet (21 percent of average). 


==================================================================================================================================
                                                       BIGHORN RIVER BASIN
                                               Streamflow Forecasts - April 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)
====================================================================|=======================|=====================================
BOYSEN RESERVOIR Inflow (2)          APR-SEP       201       272    |      320        40    |       440       616            809
                                                                    |                       |
GREYBULL RIVER nr Meeteetse          APR-SEP        72        83    |       90        45    |       106       131            201
                                                                    |                       |
SHELL CREEK nr Shell                 APR-SEP        36        40    |       42        56    |        46        53             75
                                                                    |                       |
BIGHORN RIVER at Kane (2)            APR-SEP       142       194    |      230        21    |       399       648           1124
                                                                    |                       |
==================================================================================================================================
                           BIGHORN RIVER BASIN                          |                   BIGHORN RIVER BASIN
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 2001
==================================================================================================================================
                                      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    447.2    523.6    529.3 |   NOWOOD RIVER                5        68        60
                                                                        |
BIGHORN LAKE                          1356.0    854.3    912.0    798.5 |   GREYBULL RIVER              2        75        53
                                                                        |
                                                                        |   SHELL CREEK                 4        70        66
                                                                        |
                                                                        |   BIGHORN (Boysen-Bighorn)   11        70        62
                                                                        |
==================================================================================================================================
 * 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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