Upper North Platte River Basin (8)
May 2001

Snow
The snow courses above Seminoe Reservoir have about 78 percent of average snow water equivalent (SWE) recorded for this time of the year (100 percent of last year). SWE in the drainage area above Northgate is about 75 percent of average and 80 percent of last year at this time. SWE in the Encampment River drainage is about 79 percent of normal and 108 percent of last year. Brush Creek SWE for the year is about 86 percent of normal and 120 percent of last year's SWE. Medicine Bow and Rock Creek drainage SWE is about 78 percent of average and 121 percent of last year at this time. For more information see Basin Summary of Snow Courses at the beginning of this report.

Precipitation
Nine reporting stations indicate April precipitation was 137 percent of average and about 168 percent of last year's amount. April precipitation varied from 84 to 172 percent of average. Total water-year-to-date precipitation is about 88 percent of average for the basin, which is about 101 percent of last year's amount. Year to date percentage ranges from 62 to 111 percent of average for the 9 reporting stations.

Reservoirs
Seminoe Reservoir usable storage is currently about 169 percent of normal for this time of the year. The reservoir is storing 88 percent of last year's amount. Seminoe Reservoir is estimated to be storing 663,500 acre- feet (65 percent of capacity). Last year, at this time, the reservoir had 753,000 acre-feet in storage.

Streamflow
All the following yields are based on the fifty percent chance April through September yield. Yield for the North Platte River near Northgate is expected to be about 122,000 acre-feet (54 percent of average). Encampment River near Encampment is estimated to yield 115,000 acre-feet (78 percent of normal). Rock Creek near Arlington is estimated to yield 35,000 acre-feet (64 percent of average). Seminoe Reservoir inflow should be about (415,000 acre-feet (62 percent of normal). See the following table for more detailed information on projected runoff. 

  
==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - May 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      MAY-SEP        61        97    |      122        54    |       147       183            228
                                                                    |                       |
Encampment River nr Encampment       MAY-SEP        80       101    |      115        78    |       129       150            148
                                                                    |                       |
Rock Creek nr Arlington              MAY-SEP        28        32    |       35        64    |        38        43             55
                                                                    |                       |
Seminoe Reservoir inflow             MAY-JUL       230       340    |      415        62    |       490       600            671
                                     MAY-SEP       337       407    |      455        62    |       503       573            733
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of April                 |        Watershed Snowpack Analysis - May 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    663.5    753.0    392.0 |   N PLATTE above Northgate    7        80        75
                                                                        |
                                                                        |   ENCAMPMENT RIVER            4       108        79
                                                                        |
                                                                        |   BRUSH CREEK                 5       120        86
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   3       121        78
                                                                        |
                                                                        |   N PLATTE above Seminoe     19       100        78
                                                                        |
==================================================================================================================================
 * 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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