Upper North Platte River Basin (8)
June 1999

Snow
The snow courses above Seminoe Reservoir have about 128 percent of average snow water equivalent (SWE) recorded for this time of the year (176 percent of last year). Cool weather has slowed the normal melting of snow -- consequently the comparison to average is exaggerated. SWE in the drainage area above Northgate is about 100 percent of average and 153 percent of last year at this time. SWE in the Encampment River drainage is about 127 percent of normal and 140 percent of last year. Brush Creek SWE for the year is about 190 percent of normal and 201 percent of last year's SWE. Medicine Bow and Rock Creek drainage SWE is about 156 percent of average and 268 percent of last year at this time. For more information see Basin Summary of Snow Courses at the beginning of this report.

Precipitation
Eight reporting stations indicate May precipitation was 128 percent of average and about 172 percent of last year's amount. May precipitation varied from 73 at Elk Mountain to 178 percent of average at Reno Hill SNOTEL. Total water-year-to-date precipitation is about 119 percent of average for the basin, which is about 132 percent of last year's amount. Year to date percentage ranges from 100 to 126 for the 8 reporting stations.

Reservoirs
Seminoe Reservoir is currently storing about 153 percent of normal for this time of the year. Currently, the reservoir is storing 108 percent of last year's amount. Currently, Seminoe Reservoir storage is estimated to be storing 842,900 acre-feet (83 percent of capacity). Last year, at this time, the reservoir had 777,200 acre-feet in storage.

Streamflow
All the following yields are based on the fifty percent chance June through September yield. Yield for the North Platte River near Northgate is expected to be about 170,000 acre-feet (108 percent of average). Encampment River near Encampment is estimated to yield 117,000 acre-feet (114 percent of normal). North Platte River near Sinclair will yield about 472,000 acre- feet (110 percent of normal). Rock Creek near Arlington is estimated to yield 34,000 acre-feet (81 percent of average). Medicine Bow River above Seminoe Reservoir is expected to yield about 63,000 acre-feet (98 percent of normal). Seminoe Reservoir inflow should be about (530,000 acre-feet (108 percent of normal). See the following table for more detailed information on projected runoff. 

==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - June 1, 1999
==================================================================================================================================
                                              |  <<====== 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       133       155    |      170       108    |       185       207            158
                                                                    |                       |
Encampment River nr Encampment       JUN-SEP        86       104    |      117       114    |       130       148            103
                                                                    |                       |
North Platte River nr Sinclair       JUN-SEP       365       429    |      472       110    |       515       579            431
                                                                    |                       |
Rock Creek nr Arlington              JUN-SEP        30        33    |       34        81    |        36        38             42
                                                                    |                       |
Medicine Bow River ab Seminoe Reserv JUN-SEP        44        55    |       63        98    |        72        86             64
                                                                    |                       |
Seminoe Reservoir Inflow             JUN-JUL       364       427    |      470       110    |       513       574            428
                                     JUN-SEP       354       460    |      530       108    |       600       704            491
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 1, 1999
==================================================================================================================================
                                      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    842.9    777.2    551.0 |   N PLATTE above Northgate    5       153       100
                                                                        |
                                                                        |   ENCAMPMENT RIVER            3       140       127
                                                                        |
                                                                        |   BRUSH CREEK                 2       201       190
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   2       268       156
                                                                        |
                                                                        |   N PLATTE above Seminoe     13       176       128
                                                                        |
==================================================================================================================================
 * 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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