Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 302303
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
403 PM MST Mon Jan 30 2023

.SYNOPSIS...Precipitation will gradually diminish across southern
Utah through this evening with rather abnormally cold
temperatures moving in behind it. The front will exit the area
tonight, allowing high pressure to build over the next several
days.

&&

.SHORT TERM (Through 12Z/5AM Wednesday)...Early afternoon analysis
shows a mid-level trough axis extending from a Hudson Bay low all
the way southwestward into the Great Basin. An attendant
cold/quasi-stationary front associated with this feature was
located near the AZ/UT border with Arctic air in place to the
north of the front. A closed low can be seen just off of the
southern CA coast. A ~100kt jet streak located across southern
Utah is aiding in the maintenance of modest low to mid level
frontogenesis across southern Utah, which is forcing mainly snow
showers here. Farther north, fresh, deep snowpack and ideal
radiating conditions led to dangerous cold temperatures across the
Cache and Bear River Valleys this morning, with temperatures
dropping to around -30F at the Logan Airport (coldest recorded
temperature at the Logan ASOS back to 1998), and down into the
-30F to -40F range in the Bear River Valley. These values were
colder than the NBM 5th percentile values. For tonight, have gone
with the NBM 5h percentile in the Cache and Bear River Valleys as
northern Utah is now in a neutral advection regime. Ideal
radiating conditions will once again be present tonight, so
temperatures should challenge this morning`s values. The snow
cover isn`t quite as fresh, so this could result in values just a
few degrees less cold. Nonetheless, confidence in MinTs is low
here and temperatures will remain dangerously cold.

Have upgraded and expanded the Wind Chill Watch and replaced this
with Wind Chill Warnings beginning at various times and ending at
10AM Tuesday for the Cache, Bear River Valley, SW Wyoming,
Eastern Box Elder County, Northern Wasatch Front and SW Utah.
Outside of these areas, NBM performed reasonably well, and no
manual adjustments were made to temps. This resulted in forecast
apparent Ts getting close to, but not exceeding extreme cold
criteria in Salt Lake and Utah Counties. Therefore, held off on
Wind Chill Warnings here, but we have taken steps to inform core
partners that wind chills are forecast to drop down into the 10F
to 0F range here overnight. Temperatures will be closely monitored
this evening for any possible adjustments to the forecast. Folks
should limit time outdoors, cover any exposed skin and don`t
forget about keeping pets warm and looking out for neighbors. Make
sure your vehicle is in good working order, and if traveling
include a winter survival kit.

Snow showers associated with the above-mentioned low to mid level
frontogenesis are forecast to continue overnight generally along
and south/east of a line from Kanab to Capitol Reef to Goblin
Valley. While amounts are forecast to remain generally under 1",
higher terrain areas such as fiftymile mountain and higher
elevations of Capitol Reef have ~50% chance of receiving 3" of
snow overnight. Lingering snow showers are forecast to quickly
diminish around sunrise Tuesday morning.

Gap winds in the wake of the cold front have developed across
wind-prone areas of Lower Washington County late this afternoon
with gusts around 45 mph observed. Model consensus suggest winds
either have peaked or will peak shortly, and given the relatively
short and borderline nature of these wind speeds, have opted not
to issue a wind headline for this event due to the limited nature
of the impacts (winds are generally parallel to I-15, limiting
crosswind potential).



.LONG TERM (After 12Z/5AM Wednesday)...The extended forecast will be
mostly summarized as a quieter period as a ridge builds over the
region. This will promote cold and mostly dry conditions to stick
around with the potential for some northern valleys, particularly
the Cache Valley and along the Wasatch Front, to see temperature
inversions that could lower the visibilities and air quality. Model
guidance points towards a build trough feature to move in towards
the end of the period bring potential for light snow and at the bare
minimum some mixing for areas with haze.

Temperatures on Wednesday and Thursday will be the coldest during
the extended with highs only reaching the low 30s along the Wasatch
Front and the upper teens to low 20s for the Cache Valley with
overnight temperatures in the low teens (Wasatch Front) and single
digits to negatives (Cache). By Friday the ridge starts to bring in
warmer air from the southwest ahead of a building trough feature.
Warming aloft will settle to the surface and bring back warmer
temperatures for the weekend. Confidence has been growing among
ensembles and deterministic models in a trough pattern to move into
the region by Sunday evening and bring some light snowfall to end
the weekend and start the new work week. While models such as the
GFS support an IVT to give moisture from the SW Sierra`s passage
there looks to be limitations in the building troughs extent that
will keep QPF/snowfall in the low end. For northern and central
mountains, it may be hard to break past the 0.25" QPF/ 6 inch snow
threshold, but we`ll continue to monitor trends going forward. For
valley areas, thinking total precipitation will be under 0.1" QPF
and 1-2 inches of snow. So a nice break from ridging and potential
inversion weather but little to no impacts for the CWA in terms of
snowfall.

&&

.AVIATION...KSLC...Generally quiet conditions expected behind
departing winter system. A few lower base lake effect related clouds
possible, but otherwise generally anticipate VFR conditions to
prevail with some mid/high base clouds filtering through. Winds
largely anticipated to remain light, with directional shifts near
diurnally normal times.

.REST OF UTAH AND SOUTHWEST WYOMING...A winter system will gradually
depart the region. Degraded VIS/CIGS associated with snow will
persist at southern Utah terminals through the evening, with gradual
improvement thereafter through the night as system continues to
depart. At northern terminals, quieter VFR conditions are largely
expected to prevail... Though snow pack and lingering low level
moisture, especially at sheltered sites like LGU, will yield the
chance for overnight BR/FG formation and accordingly lowered
VIS/CIGS.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Chill Warning from 8 PM this evening to 10 AM MST Tuesday
     for UTZ103-107-122.

     Wind Chill Warning from 10 PM this evening to 10 AM MST Tuesday
     for UTZ104.

     Wind Chill Warning until 10 AM MST Tuesday for UTZ109.

     Wind Chill Warning from 2 AM to 10 AM MST Tuesday for UTZ115.

     Winter Weather Advisory until 7 PM MST this evening for UTZ122-
     125.

WY...Wind Chill Warning from 10 PM this evening to 10 AM MST Tuesday
     for WYZ021.

&&

$$

ADeSmet/Selbig/Warthen

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


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