April 1999 Water Supply Outlook - Lower North Platte River Basin (9)

Lower North Platte River Basin (9)
April 1999

Snow
Most areas in the basin have received less than normal snow for this time of year. The North Platte River in Wyoming averages 85 percent of normal (100 % of last year). The Sweetwater drainage is currently 101 percent of average (136 % of last year). Deer and LaPrele Creeks are 75 percent of average (88 percent of last year). The North Platte above the Laramie River drainage is 86 percent of average (100 % of last year). The Laramie River above the mouth is 77 percent of average (95 % of last year). The Laramie River above Laramie is 80 percent of average (98 % of last year). And, the Little Laramie River is 71 percent of normal (87 percent of last year). For more information see Basin Summary of Snow Courses at beginning of report.

Precipitation
Of the 8 reporting stations, percentages for the month range from 9 to 197. March precipitation for the basin was 47 percent of average (51 percent of last year). The water year-to-date precipitation for the basin is currently 116 percent of average (127 percent of last year). Year to date percentages range from 92 to 207.

Reservoir
Lower North Platte River basin reservoir storage is average to well above average. Reservoir storage is as follows: Alcova 162,300 acre feet (100 percent of average); Glendo 505,500 acre feet (120 percent of average); Guernsey 29,900 acre feet (138 percent of average); Pathfinder 973,500 acre feet (157 percent of average); Seminoe 673,800 acre feet (183 percent of average); and Wheatland No.2 66,000 acre feet (136 percent of average). Water allocated to project use is also above average with North Platte Project users at 148 percent of average, Kendrick Project users at 120 percent of average, and Glendo Project users at 133 percent of average.

Streamflow
Yields from 48 to 114 percent are expected in the basin during the forecast period. The following yields are based on the fifty percent chance probability runoff for the April through September forecast period. The Sweetwater near Alcova is forecast to yield about 84,000 acre-feet (114 percent of average). Deer Creek at Glenrock is expected to yield about 49 percent of average (19,000 acre-feet). LaPrele Creek above the reservoir is estimated to yield 48 percent of average (12,000 acre-feet). North Platte River below Guernsey Reservoir is expected to yield about 79 percent of normal (785,000 acre-feet), and below Glendo Reservoir is anticipated to yield about 78 percent of average (754,000 acre-feet). Laramie River near Woods should yield about 89 percent of average (120,000 acre-feet). The Little Laramie near Filmore should produce about 38,000 acre-feet (59 percent of average).

==================================================================================================================================
                                      LOWER NORTH PLATTE, SWEETWATER & LARAMIE RIVER BASINS
                                               Streamflow Forecasts - April 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)
====================================================================|=======================|=====================================
Sweetwater River nr Alcova           APR-JUL        39        62    |       78       113    |        94       118             69
                                     APR-SEP        43        68    |       84       114    |       101       125             74
                                                                    |                       |
Deer Creek at Glenrock               APR-SEP       8.2      14.1    |     19.0        49    |        25        34             39
                                                                    |                       |
La Prele Creek ab La Prele Reservoir APR-JUL       2.5       7.0    |     12.0        48    |      19.0        34             25
                                                                    |                       |
North Platte River blw Glendo        APR-SEP       443              |      754        78    |                1079            963
                                                                    |                       |
North Platte River blw Guernsey      APR-SEP       455              |      785        79    |                1127            989
                                                                    |                       |
Laramie River nr Woods               APR-SEP        57        94    |      120        89    |       146       183            135
                                                                    |                       |
Little Laramie River nr Filmore      APR-SEP        21        31    |       38        59    |        45        55             64
                                                                    |                       |
==================================================================================================================================
          LOWER NORTH PLATTE, SWEETWATER & LARAMIE RIVER BASINS         |  LOWER NORTH PLATTE, SWEETWATER & LARAMIE RIVER BASINS
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 1999
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
ALCOVA                                 184.3    162.3    159.2    162.0 |   SWEETWATER                  3       136       101
                                                                        |
GLENDO                                 506.4    505.5    450.9    420.3 |   DEER & LaPRELE CREEKS       4        88        75
                                                                        |
GUERNSEY                                45.6     29.9     31.3     21.6 |   N PLATTE abv Laramie R.    27       100        86
                                                                        |
PATHFINDER                            1016.5    973.5    995.7    619.0 |   LARAMIE RIVER abv Laramie   9        98        80
                                                                        |
SEMINOE                               1016.7    673.8    766.4    368.0 |   LITTLE LARAMIE RIVER        4        87        71
                                                                        |
WHEATLAND #2                            98.9     66.0     70.0     48.7 |   LARAMIE RIVER above mouth  12        95        77
                                                                        |
NORTH PLATTE PROJ                     1062.1    999.0   1077.3    676.0 |   NORTH PLATTE               35       100        85
                                                                        |
KENDRICK PROJECT                      1201.7    973.0    939.6    812.7 |
                                                                        |
GLENDO PROJECT USERS                   183.2    169.3    168.6    127.2 |
                                                                        |
==================================================================================================================================
 * 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.
(D) - The operational measurement of flow at this point has been discountinued.

To April 1999 Basin Outlook Report Contents Page

Lower North Platte River Basin (9) April 1999

Lower North Platte River Basin (9)
April 1999