Flood and Heavy Snow in Utah, February 2 to 7, 2019

Area Forecast Discussion
National Weather Service Salt Lake City UT
1038 AM MST Sat Feb 2 2019

.SYNOPSIS...
A storm system along the California coast will move inland this
evening, then continue east across the Great Basin Sunday. A
second much colder storm system will arrive in Utah toward the
middle of the week.

&&

.DISCUSSION...The well-defined upper low parked off the central
California coast this morning will drift inland this evening. From
there this feature will become an open wave as it accelerates east
across the the Great Basin on Sunday.

A well established moisture tap ahead of the upper low has spread
across much of Utah this morning. The PWAT values running in the
0.50" to 0.60" range are well above normal for this time of year.
Synoptic-scale lift at this point remains rather weak and largely
driven by thermal advection with the upper low lagging well back
to the west. Precip so far has been light and confined to the
western half of the state. Pockets of freezing rain have been
observed across the colder valleys of far northern Utah. Suspect
this freezing rain event will end soon as available mixing clears
out any remaining cold air trapped in the valleys.

Lift will strengthen throughout the late afternoon/evening as
moist warm advection deepens with dynamic support from vorticity
lobes ejecting north ahead of the slowly advancing coastal upper
low. The heaviest precip by late this afternoon/early evening will
concentrate across southwest Utah where synoptic-scale lift will
be the strongest, with orographic influences further enhancing
precip totals.

Precipitation rates should peak between late this evening through
Sunday morning as the now open trough advances across the western
Great Basin and into Utah. Solid dynamic/thermal support for lift
along and ahead of the trough combined with the exceptionally
moist air mass will produce fairly widespread moderate to heavy
precip. Snow levels will be trending downward later tonight and
Sunday, leading to a transition from all rain to snow or
rain/snow mixed in the western valleys. The post-trough
environment will likely remain convectively unstable into early
evening as the mid-level cold pool lingers across the state
through mid-afternoon, then over the north into early evening. A
trailing shortwave Monday will utilize the lingering moisture and
produce additional convective showers on Monday.

The next Pacific storm system scheduled to arrive by late Tuesday
will be much colder than this weekend event. The initial precip
with the storm will generally be convective in nature as deep
layer cold air works into the state from the west. Widespread
snow will follow Tuesday night/Wednesday, with the heaviest precip
focusing on southern, central and eastern Utah in the areas of the
strongest lift.

&&

.AVIATION...Persistent south winds at the KSLC terminal will
be gusty near or above 25 KT through the day and continuing
overnight. Ceilings around 7k ft AGL will continue to lower through
the afternoon and below 5k ft with rain after 06z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flood Watch from 5 PM MST this afternoon through Sunday
     afternoon for UTZ019-020-518.

     Winter Weather Advisory until 5 PM MST Sunday for UTZ007>010-517.

     Winter Storm Warning until 5 PM MST Sunday for UTZ518.

WY...None.
&&

PUBLIC...CONGER
AVIATION...DEWEY

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
341 AM MST Sat Feb 2 2019

UTZ001>016-019>021-517-518-WYZ021-031400-
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-
341 AM MST Sat Feb 2 2019

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

.DAY ONE...Today and Tonight

Poor air quality and fog in the Cache Valley should improve this
morning.

A warm system will impact Utah this weekend, bringing heavy
rainfall to southern Utah. Valley rain and mid and high mountain
snow can be expected across northern Utah.

With the heavy rainfall across southern Utah this weekend, area
rivers will be running high. Slot canyons and small streams are
expected to be running high and fast. Those with outdoor plans in
these areas are urged to monitor forecasts over the next several
days.

Strong winds are expected in the mountains late today and tonight,
while western valleys may see gusty winds.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

The weekend storm will gradually end during the day Sunday.

Valley snow is expected with a colder storm Monday night into
Wednesday. Significant snow accumulations are possible. Gusty
winds will likely lead to blowing snow.

.SPOTTER INFORMATION STATEMENT...

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

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