Extended Streamflow Guidance
Issued by NWS

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FGUS65 KSTR 041910

National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
May 4, 2017


                                    MAY 1, 2017

The 2017 spring runoff flood potential due to snowmelt ruoff remains high for Weber,
Provo, Duchesne and Bear River basins of Utah at this time. This potential is due
to the much above median snow conditions in all of these areas. The threat of spring
flooding will largely be determined by hydrometeorologic events
that occur over the next 4 to 6 weeks.

Specific forecast procedures and flood flow levels do not exist for all streams,
however the CBRFC hydrologic model is forecasting above average peak flows across
north central Utah 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 flows at quite a few locations in the
Bear River, Provo River, Weber River,and Duchesne River Basins.

April precipitation was above average in the Bear, Weber, and Six Creeks Basins and below
average in the Duchesne and Provo River Basins. Snow water equivalent conditions
remain very high at all upper elevation locations across Utah. Conditions in the Weber, Provo,
Duchesne, Lower Green and Bear River basins all remain much above normal with many snow
measuring locations much above the seasonal peak snowpack. In addition,
SNOTELS have had delayed melt compared to when the melt typically begins.

The current snow water equivalent for selected Utah basins are:

Duchesne         175% of median
Weber/Ogden      145% of median
Provo            190% of median
Bear             180% of median
Six Creek        140% of median
Virgin           135% of median
Sevier            90% of median
Price/San Rafael 130% of median

Current volumetric forecasts for the April through July runoff period are much above
average for all of the above mentioned basins except those basins located in south
central and southern Utah.

Although spring temperatures affect the pattern of snowmelt runoff and consequently
the magnitude of peak flows, peak flows may roughly correspond to volumetric flows
in their magnitude. 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 during any year.

The spring runoff flood potential will be re-evaluated in mid May and an updated
product will be issued as the melt develops.

CBRFC/B.Bernard, A.Nielson, T. Cox


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