Upper Yellowstone and Madison River Basins
January 1997

Snow
Average snow water equivalent (SWE) for the SNOTEL sites is about 133 percent above normal in the Madison drainage and 113 percent above average in the Yellowstone River drainage; more than double the normal. The Madison drainage SWE is about 99 percent ahead of last year at this time. The Yellowstone drainage SWE is nearly 49 percent more than last January. See the snow course basin summary of at the beginning of this document for more details on specific sites.

Precipitation
December precipitation in the Madison and Yellowstone drainage was more than twice (270 percent above average) the normal. The 9 reporting stations in this basin indicate 1997 water year precipitation is 87 percent above normal. Water year-to-date precipitation is about 37 percent ahead of last year. December precipitation averaged 141 percent more than last years amount.

Reservoir
Reservoir storage is near normal for the reporting reservoirs. Ennis Lake is about 5 percent below average (32,100 acre feet) and Hebgen Lake's current storage is about 7 percent above normal (263,800 acre feet). See reservoir storage on the following page for details.

Streamflow
The 50 percent chance runoff is expected to be 51 to 56 percent above average for the April through September runoff period. Yellowstone at Corwin Springs has a 50 percent chance of yielding about 3,000,000 acre feet (55 percent above normal). Yellowstone near Livingston has a 50 percent chance of yielding about 3,500,000 acre feet (56 percent above normal). Madison River near Grayling has a 50 percent chance of yielding about 735,000 acre feet (51 percent above normal). See the following page for detailed runoff volumes. 

==================================================================================================================================
                                             UPPER YELLOWSTONE & MADISON RIVER BASINS
                                               Streamflow Forecasts - January 1, 1997
==================================================================================================================================
                                              |  <<====== 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       974      1102    |     1190       150    |      1278      1406            792
                                                                    |                       |
YELLOWSTONE RIVER at Corwin Springs  APR-SEP      2601      2839    |     3000       155    |      3161      3399           1937
                                                                    |                       |
YELLOWSTONE RIVER near Livingston    APR-SEP      3026      3308    |     3500       156    |      3692      3974           2241
                                                                    |                       |
MADISON RIVER near Grayling (2)      APR-SEP       647       699    |      735       151    |       771       823            486
                                                                    |                       |
==================================================================================================================================
                UPPER YELLOWSTONE & MADISON RIVER BASINS                |        UPPER YELLOWSTONE & MADISON RIVER BASINS
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 1997
==================================================================================================================================
                                      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     32.1     31.4     33.7 |   MADISON RIVER in WY         9       199       233
                                                                        |
HEBGEN LAKE                            377.5    263.8    256.8    246.8 |   YELLOWSTONE RIVER in WY     9       149       213
                                                                        |
==================================================================================================================================
 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual flow 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 flow - actual flow may be affected by upstream water management.
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