Upper Yellowstone and Madison River Basins (2)
March 2000

Snow
Snowfall in the basin this year has been just below average for the year, and very much below the SWE last year at this time. For this time of the year, snow water equivalent (SWE) is about 90 percent of average (62 percent of last year) in the Madison drainage. SWE in the Yellowstone drainage is about 91 percent of average (68 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
February precipitation in the Madison and Yellowstone drainage was about 120 percent of average (74 percent of previous year) for the 8 reporting stations -- percentage range was from 82 percent of average at Yellowstone Park to 146 percent of average at Parkers Peak SNOTEL. Water-year-to-date precipitation is about 85 percent of average (66 percent of last year's amount). Year to date percentage ranges from 66 to 112 percent

Reservoir
Ennis Lake is storing 28,200 acre-feet (83 percent of average and 69 percent of capacity). Hebgen Lake is storing about 320,600 acre-feet of water (129 percent of average and 85 percent of capacity). Hebgen Lake is storing about 111 percent and Ennis Lake is storing about 93 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 600,000 acre feet (76 percent of normal). Yellowstone at Corwin Springs will yield about 1,650,000 acre-feet (85 percent of normal). Yellowstone near Livingston will yield about 1,610,000 acre feet (85 percent of normal). Hebgen lake inflow is estimated to be 430,000 acre feet (89 percent of normal). See the following page for detailed runoff volumes. 

==================================================================================================================================
                                             UPPER YELLOWSTONE & MADISON RIVER BASINS
                                               Streamflow Forecasts - March 1, 2000
==================================================================================================================================
                                              |  <<====== 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       413       524    |      600        76    |       676       787            792
                                                                    |                       |
YELLOWSTONE RIVER at Corwin Spgs.    APR-SEP      1401      1549    |     1650        85    |      1751      1899           1937
                                                                    |                       |
YELLOWSTONE RIVER near Livingston    APR-SEP      1634      1798    |     1910        85    |      2022      2186           2241
                                                                    |                       |
HEBGEN Reservoir Inflow              APR-SEP       345       396    |      430        89    |       464       515            486
                                                                    |                       |
==================================================================================================================================
                UPPER YELLOWSTONE & MADISON RIVER BASINS                |        UPPER YELLOWSTONE & MADISON RIVER BASINS
             Reservoir Storage (1000 AF) - End of February              |        Watershed Snowpack Analysis - March 1, 2000
==================================================================================================================================
                                      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     28.2     30.3     34.1 |   MADISON RIVER in WY         9        62        90
                                                                        |
HEBGEN LAKE                            377.5    320.6    289.2    247.8 |   YELLOWSTONE RIVER in WY    12        68        91
                                                                        |
==================================================================================================================================
 * 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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