Upper North Platte River Basin (8)
March 1998

Snow
The 20 snow courses above Seminoe Reservoir average about 11 percent less than the normal Snow Water Equivalent (SWE) recorded for this time of the year (snow depths range from 31 to 79 inches). SWE in the drainage area above Northgate is about 10 percent below average and 67 percent of last year at this time. SWE in the Encampment River drainage is about 89 percent of normal and 61 percent of last year. Brush Creek SWE for the year is about 97 percent of normal and 66 percent of last year's SWE. Medicine Bow and Rock Creek drainage SWE is about 79 percent of average and 58 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 February precipitation was 1 percent below average and about 38 percent more than last year's amount. February precipitation varied from 70 percent of average at Reno Hill SNOTEL to 217 percent of average at Wamsutter. Total precipitation, for the water year to date, is 93 percent of average for the basin, which is about 70 percent of last year's amount.

Reservoirs
Seminoe Reservoir is currently storing about 105 percent more than normal for this time of the year; currently the reservoir is storing about 25 percent more than last year's storage. Seminoe Reservoir storage is estimated to be about 837,500 acre feet; last year the reservoir had 671,700 acre feet in storage.

Streamflow
The entire drainage basin is expected to have 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 270,000 acre feet (about normal); the Encampment River near Encampment is estimated to yield 145,000 acre feet (7 percent below normal); the North Platte River near Sinclair will yield about 700,000 acre feet (about 3 percent below normal); Rock Creek near Arlington is estimated to yield 51,000 acre feet (about 8 percent below average); Medicine Bow River above Seminoe Reservoir is expected to yield about 110,000 acre feet (about 13 percent below normal), Seminoe Reservoir inflow should be about (765,000 acre feet (3 percent below normal). See the following table for more detailed information on projected runoff. 

 
==================================================================================================================================
                                                  UPPER NORTH PLATTE RIVER BASIN
                                               Streamflow Forecasts - March 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       150       221    |      270       100    |       319       390            271
                                                                    |                       |
Encampment River nr Encampment       APR-SEP       101       127    |      145        93    |       163       189            156
                                                                    |                       |
North Platte River nr Sinclair       APR-SEP       408       582    |      700        97    |       818       992            719
                                                                    |                       |
Rock Creek nr Arlington              APR-SEP        34        44    |       51        91    |        59        71             56
                                                                    |                       |
Medicine Bow River ab Seminoe Reserv APR-SEP        44        80    |      110        87    |       145       206            127
                                                                    |                       |
Seminoe Reservoir Inflow             APR-JUL       465       644    |      765        97    |       886      1065            788
                                     APR-SEP       491       684    |      815        96    |       946      1139            851
                                                                    |                       |
==================================================================================================================================
                     UPPER NORTH PLATTE RIVER BASIN                     |             UPPER NORTH PLATTE RIVER BASIN
             Reservoir Storage (1000 AF) - End of February              |        Watershed Snowpack Analysis - March 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    837.5    671.7    409.0 |   N PLATTE above Northgate    8        67        90
                                                                        |
                                                                        |   ENCAMPMENT RIVER            4        61        89
                                                                        |
                                                                        |   BRUSH CREEK                 5        66        97
                                                                        |
                                                                        |   MEDICINE BOW & ROCK CREEK   3        58        79
                                                                        |
                                                                        |   N PLATTE above Seminoe     20        64        89
                                                                        |
==================================================================================================================================
 * 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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