Extended Streamflow Guidance
Issued by NWS

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000
FGUS65 KSTR 071914
ESGUT

NATIONAL WEATHER SERVICE
COLORADO BASIN RIVER FORECAST CENTER
SALT LAKE CITY, UT
MAY 7, 2019



                       FLOOD POTENTIAL OUTLOOK
                                UTAH

Great Salt Lake, Sevier, Virgin, Price/San Rafael and Duchesne
River Basins.

The 2019 spring runoff potential due to snowmelt is higher than
usual at this time for the Duchesne, San Rafael, and Sevier river
basins, somewhat elevated in the Weber, Provo, Six Creeks and
Virgin river basins, and not high for the Bear River basin.
It should be emphasized that snow typically accumulates into
April at high elevations. The threat of spring flooding will
largely be determined by hydrometeorologic events that occur
during the next two months.

In general, above average peaks are expected across most of Utah,
with highest flows, compared to average, forecast in the Duchesne,
San Rafael, and Sevier river basins. Spring flows are expected to
be higher compared to last year in all areas of Utah. Areas that
typically experience high waterin normal or above normal snow years
will be susceptible during peak runoff this year. Instantaneous peaks
can be higher than mean daily peaks, especially in headwater basins.

Spring temperatures and rain events greatly affect the pattern
of snowmelt runoff and consequently the magnitude of peak flows.
It is 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.

Water year precipitation to date (October-April) is above average in all
basins across Utah with values between 120 and 150 percent of
average. March precipitation was above to much above average.
May 1st snow water equivalent (SWE)is above much average across Utah
ranging from 120 to 180 percent of average.


PRECIPITATION AND SNOWPACK:

SUBBASIN                 APR PRECIP     OCT-APR PREC     MAY 1 SNOWPACK
----------------------   ----------     ------------     -------------
BEAR                        140             115               125
WEBER                       125             125               120
SIX CREEKS (SLC)            130             130               135
PROVO                       120             135               180
SEVIER                      155             140               155
VIRGIN                      135             150               180
DUCHESNE                    120             130               165
PRICE/SAN RAFAEL            140             145               145

The current volume forecasts for the April through July runoff period are
near to above normal across Utah river basins. Forecast volume
ranges, as a percent of average:

BEAR              85 - 150%
WEBER                 115 - 155%
SIX CREEKS (SLC)        110 - 135%
PROVO                   125 - 170%
SEVIER                  115 - 250%
VIRGIN              130 - 180%
DUCHESNE                 95 - 175%
PRICE/SAN RAFAEL        120 - 185%

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 are available at:
http://www.cbrfc.noaa.gov/lmap/lmap.php?interface=peak

Specific forecast procedures and flood flow levels do not exist
for all streams.

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

CBRFC/P.Kormos, B.Bernard, A.Nielson, Z.Finch


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