Snow Squall Warning 1, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
449 AM MST Wed Nov 9 2022

.SYNOPSIS...An area of moderate to heavy mountain snow and valley
rain/ snow mix will progress into the eastern half of Utah today,
with instability driven showers continuing for the western half of
the area. Mountain snow and few valley snow showers will linger
through early Thursday, before cold and dry conditions take over
Thursday forward.

&&

.SHORT TERM (Through 12Z/5AM Friday)...A deep upper trough,
currently centered over north-central Nevada, will continue to
slide into the area over the next 24 hours. Solid precipitation
has formed along a H7 frontogenesis axis draped essentially across
the entire length of the CWA as the 700mb frontal boundary
charges eastward. This axis will continue to shift eastward
through the morning hours, allowing for continued mountain
snowfall and valley rain that will transition over to snow.
Overnight observations have shown this storm trending warmer than
anticipated, however, several locations along the Wasatch Back and
in southern Utah (of note, Cedar City) have begun to switch over
to snowfall. Still thinking that we'll see temperatures cold
enough for snow on the Wasatch Front by ~8AM, but the
aforementioned FGEN band will be far enough east of the area that
support for any significant snowfall will be gone. That said, the
HRRR is showing the progression of an already formed convective
line / snow- squall looking feature into the central Wasatch Front
by about 7AM. It may be difficult to get much accumulating
snowfall out of this band, but it certainly may cause some reduced
visibility during the morning commute.

The aforementioned FGEN band should clear the eastern edge of our
CWA by about noon, which will coincide with the introduction with
some of the best mid-level instability. So while widespread
moderate to heavy rain/ mountain snowfall will no longer exist in
the forecast area, instability driven snow showers are likely to
continue mainly across the western half of Utah and over the
higher terrain. After about 2-3PM, model guidance is favoring a
period of mid-level drying which will help to decrease the overall
coverage of snow showers across much of Utah through the remainder
of the afternoon hours. There is indication of mid-level moisture
increasing again later in the evening which will combine with an
embedded trailing shortwave. This trailing wave is currently
expected to swing through northern Utah and southwest Wyoming
from about 6PM today to 1AM Thursday. It is likely that this
trailing wave will kick off one last round of snow showers across
northern Utah and southwest Wyoming, and this is also supported by
hi-res guidance. During this period, thinking we'll have better
chances of seeing accumulating snowfall in the valley areas, but
total accumulations should be no more than an inch (closer to 2 in
higher elevation valley areas). For the higher terrain, however,
snow ratios will be much higher later this morning and through the
afternoon, so the anticipated upslope snow showers and second
round of evening/ overnight showers should stack up snow pretty
efficiently.

Once this trailing wave clears the area early Thursday morning,
drier air will make a strong push into the region and quickly
bring any lingering snowfall to an end. Temperatures at 700mb will
reach some of their coldest temperatures of the period, bottoming
out around -15 to -16C in northern Utah, which will bring below
freezing temperatures by Thursday morning for essentially all of
Utah and southwest Wyoming. Colder temperatures will remain in
place through the remainder of the week, with a much less active
pattern ahead.

.LONG TERM (After 12Z/5AM Friday)...The long term is expected to
be much quieter and drier than the last couple of weeks. Ridging
will be in place for most of the period. Temperatures are expected
to be 15 to 20 degrees below normal during the next several days.
Most valleys are going to be in the mid 30s to near 40 degrees.
Lower Washington County will be in the mid 50s for the period.

Both deterministic and ensemble guidance is showing a weak shortwave
system moving through the area Saturday night through Sunday night.
This system is going to be accompanied by a slight increase in
moisture for the area however, the increase in moisture is light
enough that maybe some terrain induced snow showers will be
possible. The confident part of this system is that it will increase
cloud cover across the CWA. After this system, ridging will be with
us for the rest of the period. Temperatures will remain constant and
conditions will remain dry.

&&

.AVIATION...KSLC...Winds are expected to stay south for most
of the TAF period. May switch to west-southwest at times during the
day. Showers are expected to continue for the next few hours.
Isolated rain/snow showers possible between 15Z and 00Z. CIGS
expected to remain between 5kft and 7kft. These CIGS could lower as
rain/snow shower is overhead. This could lead to lower flight
categories being possible.

.REST OF UTAH AND SOUTHWEST WYOMING...Mostly southerly winds
expected for the period. Strongest gusts will be in southern and
eastern UT. Band of rain and snow will slowly move east and out of
the CWA around 21Z. After this expect isolated rain and snow showers
especially. CIGS expected to be between 4kft and 7kft before rising
higher after sunset. Lower flight categories will be possible under
a rain/snow shower.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 5 AM MST Thursday for UTZ108-109.

     Winter Storm Warning until 11 AM MST Thursday for UTZ110>112.

     Winter Storm Warning until 5 AM MST Thursday for UTZ113-117-125.

WY...Winter Weather Advisory until 5 AM MST Thursday for WYZ021.

&&

Webber / Cecava

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