Extended Streamflow Guidance
Issued by NWS

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FGUS65 KSTR 051651
ESGWY
COLORADO BASIN RIVER FORECAST CENTER
NATIONAL WEATHER SERVICE SALT LAKE CITY UTAH


                     SPRING FLOOD POTENTIAL
          FOR THE GREEN AND BEAR RIVER BASINS IN WYOMING

                       April 5, 2018


The 2018 spring runoff flood potential due to snowmelt is
higher than usual for the area above Fontenelle Reservoir and
not high in other areas of southwest Wyoming. The snowpack is
above average in the area above Fontenelle Reservoirs and near
or below average for other parts of the Upper Green River and
Bear River Basins. However, it should be emphasized that snow
typically accumulates into April and May and the threat of
spring flooding will largely be determined by hydrometeorologic
events that occur during the next several months.

Specific forecast procedures and flood flow levels do not exist
for all streams. However, currently the following sites are
forecast to peak at flood flow at the given exceedance level
(for example, there is a 10% chance the Green River nr LaBarge
will exceed flood flow):

Flood Flow:
Green River nr LaBarge               10%

March precipitation was higer than average above the Flaming
Gorge Reservoir with the exception of the Blacks Fork drainage,
and above average for the Bear River Basin. Water year
precipitation (October-March) is currently below average for
river basins in southwest Wyoming except above Fontenelle,
which is near average. Precipitation and snow conditions as of
April 1st are listed below.

PRECIPITATION AND SNOWPACK (% OF AVERAGE):

SUBBASIN                     MAR    OCT-MAR     APR 1
                          PRECIP     PRECIP      SNOW
----------------------    ------     -------     -----
GREEN ABV FONTENELLE        115        100        115
GREEN ABV FLAMING GORGE     110         90        110
BEAR RIVER HEADWATERS       110         85         70



Although spring temperatures affect the pattern of snowmelt runoff
and consequently the magnitude of peak flows, peak flows may roughly
correspond to volumetric flows. Current volume forecasts for the
April through July runoff period are above average for Fontenelle
Reservoir inflow, near average for Flaming Gorge Reservoir inflow,
and below average in other areas of southwest Wyoming.

It is also important to keep in mind that an extended period of much
above normal temperatures or heavy rainfall during the melt period can
cause or exacerbate flooding problems in any year.

The spring runoff flood potential will be re-evaluated in early May
and an updated product will be issued at that time.

A list of specific spring peak flow forecasts are available at:
http://www.cbrfc.noaa.gov/rmap/peak/peaklist.php

A map of the current spring peak flow forecasts is available at:
http://www.cbrfc.noaa.gov/lmap/lmap.php?interface=peak

CBRFC/A.Nielson

$$



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