Extended Streamflow Guidance
Issued by NWS

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000
FGUS65 KSTR 152045
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

                       FEBRUARY 15, 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 CBRFC hydrologic model is forecasting above average peak flows
across southwest Wyoming during the snowmelt runoff period. 90% exceedance
forecasts for many sites are projected to be above defined bankfull levels,
with 50% and 10% exceedance forecasts above the defined flood flow at quite
a few of those locations.

February month to date precipitation is much above average in southwest Wyoming.
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 190% of median above Fontenelle Reservoir in the
Upper Green and 160% of normal in the Bear River headwaters. A
few locations in the head waters of the Upper Green River have record
amounts of snow water equivalent for this time of year.

Current volume forecasts for the April through July runoff period
are much above average for both the Upper Green and Bear River basins.

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 early February and an updated
product will be issued at that time.

CBRFC/A.Nielson

$$








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