Upper Yellowstone and Madison River Basins (2)
January 2002

Snow
Snowfall in these basins this year has been below average for this time of the year, but better than last year. Snow water equivalent (SWE) is about 92 percent of average (159 percent of last year) in the Madison drainage. SWE in the Yellowstone drainage is about 80 percent of average (128 percent of last year at this time). See the "Snow Course Basin Summary" at the beginning of this document for more details on specific sites.

Precipitation
December precipitation in the Madison and Yellowstone drainage was about 94 percent of average (130 percent of previous year) for the 8 reporting stations -- percentage range was from 80 to 103 percent of average. Water-year-to- date precipitation is about 89 percent of average (117 percent of last year's amount). Year to date percentage ranges from 83 to 95 percent

Reservoir
Ennis Lake is storing 30,700 acre-feet (75 percent of capacity) – 97 percent of average. Hebgen Lake is storing about 295,900 acre-feet of water (78 percent of capacity) – 111 percent of average. Hebgen Lake is storing about 100 percent and Ennis Lake is storing about 100 percent of last year's volume.

Streamflow
All the following forecasts are the 50 percent chance runoff for the April through September runoff period. Yellowstone at Lake Outlet is expected to yield about 650,000 acre feet (81 percent of normal). Yellowstone at Corwin Springs will yield about 1,560,000 acre-feet (79 percent of normal). Yellowstone near Livingston will yield about 1,800,000 acre feet (79 percent of normal). Hebgen lake inflow is estimated to be 350,000 acre feet (70 percent of normal). See the following page for detailed runoff volumes. 

==================================================================================================================================
                                             UPPER YELLOWSTONE & MADISON RIVER BASINS
                                               Streamflow Forecasts - January 1, 2002
==================================================================================================================================
                                              |  <<====== 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)
====================================================================|=======================|=====================================
YELLOWSTONE at Lake Outlet           APR-SEP       470       577    |      650        81    |       723       830            805
                                                                    |                       |
YELLOWSTONE RIVER at Corwin Springs  APR-SEP      1121      1382    |     1560        79    |      1738      1999           1970
                                                                    |                       |
YELLOWSTONE RIVER near Livingston    APR-SEP      1326      1608    |     1800        79    |      1992      2274           2280
                                                                    |                       |
HEBGEN Reservoir Inflow              APR-SEP       250       309    |      350        70    |       391       450            500
                                                                    |                       |
==================================================================================================================================
                UPPER YELLOWSTONE & MADISON RIVER BASINS                |        UPPER YELLOWSTONE & MADISON RIVER BASINS
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 2002
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
ENNIS LAKE                              41.0     30.7     30.7     31.5 |   MADISON RIVER in WY         9       159        92
                                                                        |
HEBGEN LAKE                            377.5    295.9    297.0    267.6 |   YELLOWSTONE RIVER in WY    11       126        82
                                                                        |
==================================================================================================================================
 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual volume will exceed the volumes in the table.

(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.
To January 2002 Basin Outlook Report Contents Page