Upper North Platte River Basin (8)
February 1998

Snow
The 20 snow courses above Seminoe Reservoir average about 15 percent less than the normal Snow Water Equivalent (SWE) recorded for this time of the year (snow depths range from 22 to 58 inches). SWE in the draianage area above Northgate is about 14 percent below average and 55 percent of last year at this time. SWE in the Encampment River drainage is about 92 percent of normal and 55 percent of last year. Brush Creek SWE for the year is about 87 percent of normal and 56 percent of last year's SWE. Medicine Bow and Rock Creek drainage SWE is about 81 percent of average and 57 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 January precipitation was 62 percent above average and about 26 percent less than last year's amount. January precipitation varied from 91 percent of average at Reno Hill SNOTEL to 455 percent of average at Wamsutter. Total precipitation, for the water year to date, is 96 percent of average for the basin. Total precipitation for the water year is about 64 percent of last year's amount.

Reservoirs
Seminoe Reservoir is currently storing about 83 percent more than normal for this time of the year; currently the reservoir is storing about 21 percent more than last year's storage. Seminoe Reservoir storage is estimated to be about 855,100 acre feet; last year the reservoir had 707,300 acre feet in storage.

Streamflow
The entire drainage basin is expected to have a below average runoff. The April through September 50 percent chance yield for the North Platte River near the Colorado state line is expected to be 244,000 acre feet (about 10 percent less than normal); the Encampment River near Encampment is estimated to yield 131,000 acre feet (16 percent below normal); the North Platte River near Sinclair will yield about 624,000 acre feet (about 13 percent below normal); Rock Creek near Arlington is estimated to yield 48,000 acre feet (about 14 percent below average); Medicine Bow River above Seminoe Reservoir is expected to yield about 82,000 acre feet (about 35 percent below normal), Seminoe Reservoir inflow should be about (706,000 acre feet (17 percent below normal). See the following table for more detailed information on projected runoff. 

==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - February 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      APR-SEP       132       199    |      244        90    |       289       356            271
                                                                    |                       |
Encampment River nr Encampment       APR-SEP        89       114    |      131        84    |       148       173            156
                                                                    |                       |
North Platte River nr Sinclair       APR-SEP       350       513    |      624        87    |       735       898            719
                                                                    |                       |
Rock Creek nr Arlington              APR-SEP        33        41    |       48        86    |        55        67             56
                                                                    |                       |
Medicine Bow River ab Seminoe Reserv APR-SEP        30        58    |       82        65    |       111       160            127
                                                                    |                       |
Seminoe Reservoir Inflow             APR-JUL       337       528    |      657        83    |       786       977            788
                                     APR-SEP       360       566    |      706        83    |       846      1052            851
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of January               |        Watershed Snowpack Analysis - February 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    855.1    707.3    467.0 |   N PLATTE above Northgate    0         0         0
                                                                        |
                                                                        |   ENCAMPMENT RIVER            4        55        92
                                                                        |
                                                                        |   BRUSH CREEK                 5        56        87
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   3        57        81
                                                                        |
                                                                        |   N PLATTE above Seminoe     12        55        86
                                                                        |
==================================================================================================================================
 * 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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