Extended Streamflow Guidance
Issued by NWS

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FGUS65 KSTR 062128
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 6, 2017


The 2017 spring runoff flood potential due to snowmelt is
high for Upper Green and Bear River basins in southwest
Wyoming at this time due to much above normal snow conditions
in these areas. 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 25% chance the New Fork River nr Big Piney will
exceed flood flow):

Flood Flow:
New Fork River nr Big Piney          25%
Green River nr LaBarge               90%
Green River nr Green River           25%
Hams Fork River nr Pole Creek        10%
Bear River nr Evanston               10%
Bear River nr Border                 90%

March precipitation was much above average in southwest Wyoming.
Water year precipitation in southwest Wyoming is currently 180%.
The snow water equivalent in the Upper Green and Bear River basins is much
above normal with most locations having already exceeded the annual
peak snowpack which typically occurs in April or May. The current snow water
equivalent is 170% of median above Fontenelle Reservoir in the Upper
Green and 135% of normal in the Bear River headwaters. March temperatures were
much above average which resulted in significant low elevation snowmelt.
As a result, soil conditions are saturated in many of the low elevation areas.
Areas with saturated soil conditions may experience more responsive and
efficient runoff with the additional rain or snowmelt.

Current volume forecasts for the April through July runoff period
are much above average for both the Upper Green and Bear River basins.
April 1st forecasted volumes are near or above record for Fontenelle
and Flaming Gorge reservoir inflows.

Although spring temperatures affect the pattern of snowmelt runoff and
consequently the magnitude of peak flows, peak flows may roughly correspond
to volumetric flows. 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 mid April 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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