National Weather Service Text Product Display

Extended Streamflow Guidance
Issued by NWS
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FGUS65 KSTR 061359
ESGUT

NATIONAL WEATHER SERVICE
COLORADO BASIN RIVER FORECAST CENTER
SALT LAKE CITY, UT
May 6, 2021

                       FLOOD POTENTIAL OUTLOOK
                                UTAH


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

Spring 2021 peak flows due to snowmelt runoff are expected to be below
average across all basin in Utah which include the Bear, Weber, Provo,
Six Creeks, Sevier, Virgin, San Rafael, Price, Green and Duchesne River Basins.

Currently no sites are forecast to reach mean daily flood flow levels, even
in the 10% exceedence catagory. Specific forecast procedures and flood flow
levels do not exist for all streams in Utah.

The snowpack remains below normal and it is probable that the peak snow
accumulation has already past, as melt has already occured at many snotel
stations, even above 9000`.

In general, near to below average peaks are expected across most of Utah.
Instantaneous peaks can be higher than forecast mean daily peaks,
especially in headwater basins.

Spring weather 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, clear skies, or heavy rainfall and
associated high winds during the melt period can cause or exacerbate
flooding problems in any year.


PRECIPITATION (% OF AVERAGE) AND SNOWPACK (% OF MEDIAN):

SUBBASIN                 APR PRECIP     OCT-APR PREC       MAY 1 SNOWPACK
----------------------   ----------     ------------     -------------
BEAR                         60              70                60
WEBER                        60              65                55
SIX CREEKS (SLC)             75              75                75
PROVO                        55              65                35
SEVIER                       45              65                45
VIRGIN                       50              55                20
DUCHESNE                     60              70                55
PRICE/SAN RAFAEL             45              65                25

The current volume forecasts for the April through July runoff period,
as of May 1, 2021 are below to much below normal across Utah river basins.
Forecasted volumes range, as a percent of average as follows:

BEAR              10 - 55%
WEBER                15 - 45%
SIX CREEKS (SLC)     20 - 60%
PROVO                20 - 50%
SEVIER               10 - 75% Regulated
VIRGIN               20 - 20%
DUCHESNE             25 - 55%
PRICE/SAN RAFAEL     10 - 40%

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

The spring runoff flood potential will be re-evaluated mid May and updated
forecasts will be issued at that time.

CBRFC/P.Kormos, B.Bernard, Z.Finch
National Weather Service National Headquarters
