Extended Streamflow Guidance
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National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
April 6, 2017

                 INTERNAL NWS PRODUCT FOR GUIDANCE PURPOSES ONLYs

                        SPRING FLOOD POTENTIAL OUTLOOK UTAH
                                    APRIL 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. It should also be
emphasized that snow typically accumulates into mid April and even May and that
the threat of spring flooding will largely be determined by hydrometeorologic events
that occur during the next 2 months.

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 flow at quite a few locations in the
Bear, Logan, Duchesne, Blacksmith Fork, Little Bear, Chalk Creek, Provo at Woodland
and Weber at Oakley.

March precipitation was above average in the Bear Basin and near average in the Duchesne.
In Six Creek, the Provo, Sevier and Virgin basins March precipitation was below average.
Snow water equivalent however is a different story. Conditions in the Weber, Provo,
Duchesne, Green and Bear River basins remain much above normal with many of our snow
gaging locations above peak snowpack which typically occur in mid April and May. The
current snow water equivalent are:

Duchesne 165% of median
Weber/Ogden 130% of median
Provo 145% of median
Bear 145% of median
Six Creek 125% of median
Virgin 130% of median
Sevier 130% of median
Price/San Rafael 130% of median

Many of Utah`s SNOTEL`s were ranked in the top 3 highest years for the period of
record in early March however a very warm and mostly dry month melted a great deal
of snow below 7000 feet and lowered April through July volumes in all but the Green,
Duchesne and Bear River Basins.

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 late April and an updated
product will be issued the first week of May.


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

NNNN
$$




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