Upper North Platte River Basin (8)
June 1998

Snow
The 13 snow courses above Seminoe Reservoir average about 73 percent of average snow water equivalent (SWE) recorded for this time of the year (52 percent of last year). SWE in the drainage area above Northgate is about 65 percent of average and 49 percent of last year at this time. SWE in the Encampment River drainage is about 91 percent of normal and 56 percent of last year. Brush Creek SWE for the year is about 94 percent of normal and 75 percent of last year's SWE. Medicine Bow and Rock Creek drainage SWE is about 58 percent of average and 43 percent of 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 83 percent of average and about 66 percent of last year's amount. May precipitation varied from 49 percent of average at Reno Hill SNOTEL to 100 percent of average at Rawlins FAA. Total water-year-to-date precipitation is about 92 percent of average for the basin, which is about 74 percent of last year's amount.

Reservoir
Seminoe Reservoir is currently storing about 141 percent of normal for this time of the year. Currently the reservoir is storing about the same as last year. Seminoe Reservoir storage is estimated to be 777,200 acre feet. Last year, at this time, the reservoir had 785,400 acre feet in storage.

Streamflow
The entire drainage basin is expected to have below average runoff. All the following yields are based on the fifty percent chance June through September yield. Yield for the North Platte River near the Colorado state line is expected to be 92,000 acre feet (58 percent of average). Encampment River near Encampment is estimated to yield 93,000 acre feet (90 percent of normal). North Platte River near Sinclair will yield about 305,000 acre feet (about 71 percent of normal). Rock Creek near Arlington is estimated to yield 31,000 acre feet (about 74 percent of average). Medicine Bow River above Seminoe Reservoir is expected to yield about 29,000 acre feet (about 45 percent of normal). Seminoe Reservoir inflow should be about (290,000 acre feet (68 percent of normal). See the following table for more detailed information on projected runoff. 

==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - June 1, 1998
==================================================================================================================================
                                              |  <<====== 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 nr Northgate      JUN-SEP        55        77    |       92        58    |       107       129            158
                                                                    |                       |
Encampment River nr Encampment       JUN-SEP        62        80    |       93        90    |       106       124            103
                                                                    |                       |
North Platte River nr Sinclair       JUN-SEP       198       262    |      305        71    |       348       412            431
                                                                    |                       |
Rock Creek nr Arlington              JUN-SEP        28        30    |       31        74    |        33        35             42
                                                                    |                       |
Medicine Bow River ab Seminoe Reserv JUN-SEP      16.4        24    |       29        45    |        35        45             64
                                                                    |                       |
Seminoe Reservoir Inflow             JUN-JUL       184       247    |      290        68    |       333       396            428
                                     JUN-SEP       156       260    |      330        67    |       400       504            491
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 1, 1998
==================================================================================================================================
                                      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    777.2    785.4    551.0 |   N PLATTE above Northgate    5        49        65
                                                                        |
                                                                        |   ENCAMPMENT RIVER            3        56        91
                                                                        |
                                                                        |   BRUSH CREEK                 2        75        94
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   2        43        58
                                                                        |
                                                                        |   N PLATTE above Seminoe     13        52        73
                                                                        |
==================================================================================================================================
 * 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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