Extended Streamflow Guidance
Issued by NWS

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000
FGUS65 KSTR 042313
ESGUT

NATIONAL WEATHER SERVICE
COLORADO BASIN RIVER FORECAST CENTER
SALT LAKE CITY, UT
APRIL 4, 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.

Currently, the following sites are forecast to have mean
daily peak flows at or above the flood flow at the given
exceedance level:

Duchesne near Randlett                   10%

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 with the exception
of the Bear River basin. Areas that typically experience high water
in 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-March) 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.
April 1st snow water equivalent (SWE)is above much average across Utah
ranging from 120 to 185 percent of average.

PRECIPITATION AND SNOWPACK:

SUBBASIN                 MAR PRECIP     OCT-MAR PREC     APR 1 SNOWPACK
----------------------   ----------     ------------     -------------
BEAR                        110             120               120
WEBER                       145             125               125
SIX CREEKS (SLC)            145             130               135
PROVO                       155             140               145
SEVIER                      155             140               150
VIRGIN                      150             150               185
DUCHESNE                    135             135               145
PRICE/SAN RAFAEL            185             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 - 140%
WEBER             105 - 165%
SIX CREEKS (SLC)        100 - 130%
PROVO                   120 - 160%
SEVIER                  130 - 170%
VIRGIN          110 - 120%
DUCHESNE                 95 - 160%
PRICE/SAN RAFAEL        120 - 175%

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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