Flash Flooding and Flood in Utah, September 14 to 15, 2017

Area Forecast Discussion
National Weather Service Salt Lake City UT
1018 PM MDT Wed Sep 13 2017

.SYNOPSIS...A series of storm systems will bring cooler and
wetter conditions to Utah and southwest Wyoming Thursday and
Friday. A milder southwesterly flow will return for the weekend.

&&

.DISCUSSION...The low over the California coast will continue to
slowly make its way inland overnight. Meanwhile, Utah remains under
a west-southwesterly flow downstream of this low. A few areas of
showers and thunderstorms are noted over the forecast area. First,
there is northwest Utah, where a weak shortwave disturbance ejecting
towards the northeast is impinging on the deformation axis across
far northwest Utah and southern Idaho. The second area is southeast
Utah where another weak disturbance exists with some lingering
instability. The third area is southern Nevada into far southwest
Utah which is starting to see increasing diffluence aloft.

The expectation is that showers across northwest Utah will continue
to progress east into the Wasatch Front area tonight. Meanwhile, the
showers across the southwest Utah will likely continue and spread
across west-central Utah late tonight, as the upper low continues to
make inland progress. Meanwhile, the showers across the southeast is
expected to gradually wane.

As the low tracks into Utah and gradually transition to an open
wave, expect precipitation to increase tomorrow, first across
southwest Utah in the morning and south-central through east-central
Utah by the afternoon. A 70-80kt upper jet will accompany this storm
system, and shear profile still looks good for some organized storms
given enough instability. Some of the stronger storms will be
capable of producing heavy rain as well.

Otherwise, a second storm system will follow Thursday night into
Friday, dropping a wet cold front into the area from the north.
Temperatures will be significantly cooler for Friday and Saturday.

&&

.AVIATION...Generally southerly winds are expected across the SLC
terminal through much of the night. However, there is a 25 percent
chance of thunderstorms after 06z. These thunderstorms may bring a
period of gusty and erratic winds. Otherwise, VFR conditions are
expected, although CIGS may briefly fall below 7kft in heavier
showers.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

Cheng

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php

Hazardous Weather Outlook
National Weather Service Salt Lake City UT
348 AM MDT Wed Sep 13 2017

UTZ001>016-019>021-517-518-WYZ021-141300-
Cache Valley/Utah Portion-Northern Wasatch Front-
Salt Lake and Tooele Valleys-Southern Wasatch Front-
Great Salt Lake Desert and Mountains-Wasatch Mountain Valleys-
Wasatch Mountains I-80 North-Wasatch Mountains South of I-80-
Western Uinta Mountains-Wasatch Plateau/Book Cliffs-
Western Uinta Basin-Castle Country-San Rafael Swell-
Sanpete/Sevier Valleys-West Central Utah-Southwest Utah-
Utahs Dixie and Zion National Park-South Central Utah-
Glen Canyon Recreation Area/Lake Powell-Central Mountains-
Southern Mountains-Southwest Wyoming-
348 AM MDT Wed Sep 13 2017

This Hazardous Weather Outlook is for the western two thirds of
Utah and southwest Wyoming.

.DAY ONE...Today and Tonight

Isolated to scattered showers and thunderstorms may bring locally
gusty and erratic winds.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Tomorrow, the first in a series of storm systems will bring
widespread precipitation to southern and eastern Utah, increasing
flash flood risk while bringing the possibility of hail and strong
winds.

A strong cold front will bring significantly cooler temps to the
outlook area beginning Friday. Widespread precipitation is
expected across the north and west, coupled with temperatures
some 10 to 15 degrees below average. Lowering snow levels will
have the potential to allow light accumulations for elevations
over 8000 to 9000 feet across the northern mountains. Hunters,
hikers, and others with outdoor and backcountry plans should be
prepared for raw conditions.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to standard operating procedures.

Rogowski/Merrill

For more information from NOAA/s National Weather Service visit...
http://weather.gov/saltlakecity

For information on potential road travel impacts visit...
http://www.udottraffic.utah.gov/roadweatherforecast.aspx