Upper North Platte River Basin
May 1997

Snow
The 20 snow courses above Seminoe Reservoir average about 32 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 2 percent more than last year at this time. SWE in the Encampment River drainage is about 39 percent more than normal and 18 percent more than last year. Brush Creek SWE for the year is about 19 percent more than normal and 1 percent more than last year. The Medicine Bow and Rock Creek drainage SWE is about 26 percent above average and 17 percent above 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 April precipitation was 28 percent above average and about 8 percent less than last year's amount. April precipitation varied from 74 percent of average at South Brusk Creek to 204 percent of average at Willow Creek. 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 8 percent more than last year's amount.

Reservoirs
Seminoe Reservoir is currently storing about 56 percent more than normal for this time of the year; currently the reservoir is storing about 3 percent less than last year's storage. Seminoe Reservoir storage is estimated to be about 611,000 acre feet; last year the reservoir had 627,500 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 375,000 acre feet (about 38 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 990,000 acre feet (about 38 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 185,000 acre feet (about 46 percent above normal). Seminoe Reservoir inflow is estimated to be 1,100,000 acre feet (38 percent above normal). See the following table for more detailed information on projected runoff. 

==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - May 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       312       349    |      375       138    |       401       439            271
                                                                    |                       |
ENCAMPMENT RIVER near Encampment     APR-SEP       196       213    |      225       144    |       237       254            156
                                                                    |                       |
NORTH PLATTE RIVER near Sinclair     APR-SEP       818       920    |      990       138    |      1060      1162            718
                                                                    |                       |
ROCK CREEK nr Arlington              APR-SEP        58        65    |       70       121    |        75        82             58
                                                                    |                       |
MEDICINE BOW RIVER nr Hanna          APR-SEP       146       169    |      185       146    |       201       224            127
                                                                    |                       |
SEMINOE RESERVOIR INFLOW             APR-JUL       974      1049    |     1100       138    |      1151      1226            800
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 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    611.0    627.5    392.0 |   N PLATTE above Northgate    8       102       134
                                                                        |
                                                                        |   ENCAMPMENT RIVER            4       118       139
                                                                        |
                                                                        |   BRUSH CREEK                 5       101       119
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   3       117       126
                                                                        |
                                                                        |   N PLATTE above Seminoe     20       108       132
                                                                        |
==================================================================================================================================
 * 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.
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