Flash Flood and High Wind in Utah, November 19, 2023

Area Forecast Discussion
National Weather Service Salt Lake City UT
505 AM MST Sun Nov 19 2023

.SYNOPSIS...A winter storm will impact much of the state Sunday
into early Monday. High pressure will build into the area for the
first part of the week, with the next potential storm arriving
just in time for Thanksgiving.

&&

.SHORT TERM (Through 12Z/5AM Tuesday)...A strong storm will
impact much of the area during the short term period. A trough is
currently digging into the Great Basin region and will continue to
do so during the morning hours before shifting east through the
rest of the day Sunday and into Monday. This storm will bring
heavy mountain snow for much of Utah as well as gusty northwest
winds, especially for northwestern Utah and Castle Country. Gap
winds will also be problem as the trough exits the region on
Sunday night into Monday morning.

Current upper air and satellite analysis shows an area of
diffluence at 500mb that will translate south and eastward
through the morning hours. This will bring an increased chance of
rain as well as thunderstorms to southern Utah. Outside of this,
current radar analysis shows precipitation occurring for most
areas along the I-15 corridor and westward to the Nevada border.
This precipitation will continue through the morning and into the
afternoon along and ahead of a baroclinic zone associated with
this trough, before consolidating mainly north of I-70 and in
elevated terrain areas. Precipitation is expected to end across
the Utah and southwest Wyoming by mid- Monday morning.

Focusing on the snow aspect of this storm, snow levels will start
out near 7000ft before dropping throughout the day Sunday. Snow
levels will potentially drop to valley floors between 03Z and 06Z
Monday. This means that snow would be possible at valley floors,
however any accumulation is expected to be minimal. Some snow
accumulation is expected for the benches especially on grassy
surfaces. Some road slush is also possible for these higher
elevation areas. Most of the significant snow accumulations are
expected for areas above 6000ft. Current snow totals for most
mountains in Utah are between 10 inches and 18 inches with locally
higher amounts. Something to consider for these totals would be
how long the upper-level flow stays northwest for the favored
locations of this wind direction. If the flow changes to north,
which it will eventually, sooner than anticipated, then snow
totals in these favored locations, such as the Upper Cottonwoods
would largely be shut off. Another thing to note is that the
greatest area of upper-level flow combined with the best moisture
potential is only up to ~600mb. Once the back side of the trough
moves into Utah, drier air will entrain quickly into Utah, thus
cutting off the potential for orographic flow sometime early
Monday morning.

The aforementioned baroclinic zone will also bring strong
northwesterly winds with it. Downsloping winds will be possible in
areas of favored flow direction, especially northwestern Utah and
Castle Country. Gap winds will also be a problem late Sunday night
through Monday morning as there will be a strong thermal gradient
combining with 25kt to 40kt winds at 700mb.

.LONG TERM...Behind the departing trough, mid level ridging will
bring dry and stable conditions across the region through midweek.
This will bring a warming trend most notable across the higher
elevations, while northern and central valleys will likely
experience a more muted warming trend owing to limited mixing.

A Thanksgiving trough is still advertised in the models, however
there remains a substantial amount of spread in the guidance,
ranging from a less amplified wave impacting mainly northern Utah,
to a much deeper upper trough digging through the region. The
former solution would primarily impact northern Utah, while the
latter would bring widespread precipitation to the state, along
with much colder temperatures Thanksgiving Day through Friday.
Blended guidance (NBM) has trended colder and wetter during this
timeframe, favoring a deeper and colder system across the region.
A lot of details still need to be ironed out, and those planning
holiday travel should continue to monitor future forecasts
regarding this potentially impactful weather system.

&&

.AVIATION...KSLC...Periods of rain will result in MVFR conditions
through this morning. Winds will hold a predominantly northerly
component, but will become gusty and variable at times.
Precipitation becomes more showery through the afternoon with VFR
conditions prevailing, however CIGS will likely remain below 6
kft, and passing showers will drop conditions into MVFR or high
end IFR at times. There is a 20-30% chance for snow showers
reducing conditions into IFR to LIFR between 23z-05z, with no
accumulation expected.

.REST OF UTAH AND SOUTHWEST WYOMING...A storm system moving
through the region will bring periods of MVFR to IFR conditions
throughout the day. Gusty northwest winds in excess of 30 kts will
be possible at KENV and KBCE later on this afternoon and evening.
Lowering snow levels may bring IFR to LIFR conditions to
terminals above 5 kft late this morning through this afternoon.
Conditions will largely return to VFR this evening across the
region, with gusty winds continuing across southern Utah.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...High Wind Warning from 8 AM this morning to 11 PM MST this
     evening for UTZ101.

     Winter Storm Warning until 3 AM MST Monday for UTZ110>112.

     Winter Storm Warning until 11 PM MST this evening for UTZ113-117.

     Wind Advisory from 5 PM this afternoon to 11 AM MST Monday for
     UTZ120.

     High Wind Warning from 5 PM this afternoon to 11 AM MST Monday
     for UTZ123.

     Winter Storm Warning until 11 PM MST this evening for UTZ125.

WY...None.
&&

Cecava/Seaman

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