Upper North Platte River Basin (8)
June 1997

Snow
The 13 snow courses above Seminoe Reservoir average about 39 percent more than the normal Snow Water Equivalent (SWE) recorded for this time of the year. In Colorado (above Northgate), SWE is about 34 percent above average and 26 percent more than last year at this time. SWE in the Encampment River drainage is about 62 percent more than normal and 24 percent more than last year. Brush Creek SWE for the year is about 25 percent more than normal and 25 percent less than last year. The Medicine Bow and Rock Creek drainage SWE is about 37 percent above average and 1 percent below last year at this time. For more information see Basin Summary of Snow Courses at the beginning of this report.

Precipitation
Eleven reporting stations indicate May precipitation was 30 percent above average and about 3 percent less than last year's amount. May precipitation varied from 83 percent of average at Seminoe Dam to 243 percent of average at Reno Hill SNOTEL. Total precipitation, for the water year to date, is 23 percent more than average for the basin. Total precipitation for the water year is about 7 percent more than last year's amount.

Reservoirs
Seminoe Reservoir is currently storing about 46 percent more than normal for this time of the year; currently the reservoir is storing about 1 percent less than last year's storage. Seminoe Reservoir storage is estimated to be about 785,400 acre feet; last year the reservoir had 780,800 acre feet in storage.

Streamflow
The entire drainage basin is expected to have an above average runoff. The April through September 50 percent chance yield for the North Platte River near the Colorado state line is expected to be 390,000 acre feet (about 44 percent more than normal); the Encampment River near Encampment is estimated to yield 225,000 acre feet (44 percent above normal); the North Platte River near Sinclair will yield about 1,025,000 acre feet (about 43 percent above normal); Rock Creek near Arlington is estimated to yield 70,000 acre feet (about 21 percent above average); Medicine Bow River near Hanna is expected to yield about 200,000 acre feet (about 58 percent above normal). See the following table for more detailed information on projected runoff. 

==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - June 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)
====================================================================|=======================|=====================================
NORTH PLATTE RIVER near Northgate    APR-SEP       329       365    |      390       144    |       415       451            271
                                                                    |                       |
ENCAMPMENT RIVER near Encampment     APR-SEP       197       214    |      225       144    |       236       253            156
                                                                    |                       |
NORTH PLATTE RIVER near Sinclair     APR-SEP       855       956    |     1025       143    |      1094      1195            718
                                                                    |                       |
ROCK CREEK nr Arlington              APR-SEP        61        66    |       70       121    |        74        79             58
                                                                    |                       |
MEDICINE BOW RIVER nr Hanna          APR-SEP       170       188    |      200       158    |       212       230            127
                                                                    |                       |
SEMINOE RESERVOIR INFLOW             APR-JUL      1023      1092    |     1140       143    |      1188      1257            800
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 1, 1997
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
SEMINOE                               1016.7    785.4    780.8    551.0 |   N PLATTE above Northgate    5       126       134
                                                                        |
                                                                        |   ENCAMPMENT RIVER            3       124       162
                                                                        |
                                                                        |   BRUSH CREEK                 2        75       125
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   2        99       137
                                                                        |
                                                                        |   N PLATTE above Seminoe     13       112       139
                                                                        |
==================================================================================================================================
 * 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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