Upper North Platte River Basin (8)
June 2001

Snow
The snow courses above Seminoe Reservoir have about 29 percent of average snow water equivalent (SWE) recorded for this time of the year (80 percent of last year). SWE in the drainage area above Northgate is about 28 percent of average and 64 percent of last year at this time. SWE in the Encampment River drainage is about 27 percent of normal and 95 percent of last year. Brush Creek SWE for the year is about 32 percent of normal and 74 percent of last year's SWE. Medicine Bow and Rock Creek drainage SWE is about 34 percent of average and 114 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 67 percent of average and about 74 percent of last year's amount. May precipitation varied from 15 to 224 percent of average. Total water-year-to-date precipitation is about 85 percent of average for the basin, which is about 93 percent of last year's amount. Year to date percentage ranges from 56 to 108 percent of average for the 9 reporting stations.

Reservoirs
Seminoe Reservoir usable storage is currently about 136 percent of normal for this time of the year. The reservoir is storing 82 percent of last year's amount. Seminoe Reservoir is estimated to be storing 751,100 acre-feet (74 percent of capacity). Last year, at this time, the reservoir had 914,200 acre-feet in storage.

Streamflow
Yields in the North Platte River drainage will be well below normal. Irrigators diverting water directly from a stream may experience water shortages. 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 89,000 acre-feet (56 percent of average). Encampment River near Encampment is estimated to yield 66,000 acre-feet (64 percent of normal). Rock Creek near Arlington is estimated to yield 20,000 acre-feet (48 percent of average). Seminoe Reservoir inflow should be about (280,000 acre-feet (57 percent of normal). See the following table for more detailed information on projected runoff. 

 
==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - June 1, 2001
==================================================================================================================================
                                              |  <<====== 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        56        76    |       89        56    |       102       122            158
                                                                    |                       |
Encampment River nr Encampment       JUN-SEP        50        60    |       66        64    |        79        97            103
                                                                    |                       |
Rock Creek nr Arlington              JUN-SEP      17.2      18.8    |       20        48    |        21        23             42
                                                                    |                       |
Seminoe Reservoir inflow             JUN-JUL       134       197    |      240        56    |       283       346            428
                                     JUN-SEP       203       249    |      280        57    |       311       357            491
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 1, 2001
==================================================================================================================================
                                      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    751.1    914.2    551.0 |   N PLATTE above Northgate    5        64        28
                                                                        |
                                                                        |   ENCAMPMENT RIVER            3        95        27
                                                                        |
                                                                        |   BRUSH CREEK                 2        74        32
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   2       114        34
                                                                        |
                                                                        |   N PLATTE above Seminoe     13        80        29
                                                                        |
==================================================================================================================================
 * 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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