Heavy Snow in Utah, November 28 to 30, 2022

Area Forecast Discussion
National Weather Service Salt Lake City UT
359 PM MST Sun Nov 27 2022

.SYNOPSIS...A storm will impact much of the state Monday into
Tuesday, with a much colder airmass settling in for midweek. Another
storm is expected Friday into Saturday.

&&

.SHORT TERM (Through 00Z Wednesday)...Afternoon upper air and
satellite analysis indicates an upper level trough shifting south
from Canada into the northern tier of the West. Meanwhile, a
north/south oriented jet from near the arctic circle south to the
PACNW is located on the west side of the developing longwave
trough.

While there is no precipitation on radar now, this will be
temporary as the longwave trough shifts southward through Tuesday.

A winter storm will impact much of Utah Monday into Tuesday. This
storm will likely feature two main parts...at least for northern
Utah. By Monday morning, moist westerly flow will result in
orographically enhanced precipitation across portions of northern
Utah, especially in normally favored locations such as the
northern Wasatch Front benches Ogden area mountains, and the Bear
River Range. During this time, net mid-level cold air advection
will be ongoing. A weak surface front will enter northern Utah
Monday morning.

With increasing favorable jet dynamics, the cold front will
strengthen during a period of frontogenesis, likely somewhere near
Ogden near 21Z. This is expected to help develop a band of
moderate to heavy snow that will impact portions of the Wasatch
Front and adjacent mountains during the Monday evening commute.
Model soundings indicate the potential for significant lift within
the dendritic growth zone. All this to say, there may be a period
of snow rates near 1-2 inches an hour with this boundary from
roughly Ogden southward during the Monday evening
commute...especially along the benches.

Once the front clears the area, deep, moist northwest flow will
continue across northern Utah, favoring the usual suspect for
orographic enhancement (such as the Cottonwoods). During this
portion of the storm, some locations may see snow decrease or even
stop for a time...but the next shortwave trough will bring another
round of snow to portions of northern and central Utah Monday
night into at least Tuesday morning.

The big question mark is the potential for lake effect snow,
primarily for locations from Bountiful south to Salt Lake County.
With 700mb temperatures near -14 to -16C (with the lake near
3-4C), deep moisture and northwesterly flow, expect the threat of
lake effect snow or lake enhanced snow showers to impact these
locations. Notably, the breadth of available CAMS show a discrete,
heavy lake effect snow band impacting Salt Lake County into the
Cottonwoods Monday night into Tuesday morning.

Lake effect snow bands are difficult to predict with this much
lead time down to specific locations and snow accumulations as a
result of these bands depend on whether the band is fairly
persistent and stationary or more prone to a wavering portion.
However, expect at least some lake effect/lake enhanced snow will
impact the Tuesday morning commute for a portion of far southern
Davis or Salt Lake County (and potentially the Santaquin to
Spanish Fork area off Utah Lake). If this does occur and the band
is discrete and persistent in one location, forecast snow totals
will be on the low side.

Issued winter weather advisories for the Wasatch Front from
Weber/Davis County south to Utah County as well as the Wasatch
Back and Uinta County, WY. Also added the central and southern
mountains...based on the expect impact to mountain routes.
Will need to monitor the potential for upgrades either with a
significant impact to either the Monday evening or Tuesday morning
commutes, or an expected discrete, heavy snow area of lake effect
snow.

.LONG TERM (After 00Z Wednesday)...Cold conditions are expected at
the beginning of the long term. As a trough exits the region, cold
air will follow behind it. This will bring temperatures down to 10
to 15 degrees below average. Low temperatures Wednesday morning will
be near zero or slightly below zero for some northeastern UT valleys
and Uinta County WY. As for most of the other valleys temperatures
will be in the single digits to mid teens. Lower Washington County
is expected to be in the mid to upper 20s. Prior to the cold air on
Wednesday morning, some lingering mountain snow showers will be
possible Tuesday night.

After this trough moves out, ridging will take over the area and
provide a brief break before another trough effecting our area later
this week. Temperatures are expected to rebound from Wednesday
morning and be closer to average, however this may not be the case
as valley inversions could form pending on how much snow is on the
ground from the early week storm. Southwest flow kicks in ahead of
the incoming trough which will result in gusty southwest winds
during the day on Thursday. Currently these wind gusts are around
advisory level for western UT. This will be something to monitor to
see if wind headlines will be needed for Thursday.

Another aspect of this trough to watch out for is the potential for
an atmospheric river (AR) event to occur. Guidance is growing in
confidence that where the trough is positioned at will lead to
increased amounts of moisture across the western US. For our CWA,
PWAT values of 0.3" to 0.5" are expected between Thursday and
Friday. Any moisture that does fall will begin as rain in the
valleys and snow in the mountains. Valleys will see a greater chance
at snow when the cold air advection moves in Friday
afternoon/evening. There is a decent amount of uncertainty regarding
this AR event. Both ensemble and deterministic guidance agree that
the trough will move inland but the timing and location of this
inland push are uncertain. A cold front is also expected to move
through the area but guidance shows it moving through either Friday
or Saturday.

&&

.AVIATION...KSLC...VFR conditions will persist overnight and
gradually transition to MVFR and brief periods of IFR/LIFR
conditions tomorrow afternoon. Winds will remain southerly through
tomorrow afternoon before transitioning northwesterly behind a
cold front. As the day progresses precipitation will reach valley
floors with a few snow showers during the afternoon creating MVFR
conditions with periods of IFR/LIFR conditions under heavier
bursts of snow, particularly between 22-01Z.

.REST OF UTAH AND SOUTHWEST WYOMING...For northern Utah/SW
Wyoming, VFR conditions will gradually transition to the MVFR and
brief periods of IFR/LIFR conditions terminals as a winter storm
approaches tomorrow morning. As the day progresses precipitation
will reach valley floors with a few snow showers during the
afternoon creating MVFR conditions with periods of IFR conditions
under heavier bursts of snow. These spotty snow showers will
transition to a band of moderate to heavy snow as the main cold
front arrives between 22-01Z. Conditions will likely reduce VIS and
CIGs to IFR/LIFR levels for 1-2 hours. Ahead of the cold front winds
will remain southerly ~10kts. Behind the cold front winds will
transition to northwesterly. After the main frontal snow band pushes
through there is a possibility of a lake effect snow band setting up
southeast of the Great Salt Lake late Monday into early Tuesday.
Heavy snow will accompany this band and will reduce VIS and CIGs to
IFR/LIFR.

For southern Utah, VFR conditions will prevail through most of the
period as the aforementioned storm won't arrive until after 00Z
Tuesday.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from 2 PM Monday to 2 PM MST Tuesday for
     UTZ102-104>106.

     Winter Weather Advisory from 7 AM Monday to 2 PM MST Tuesday for
     UTZ108.

     Winter Weather Advisory from 5 AM Monday to noon MST Tuesday for
     UTZ110.

     Winter Weather Advisory from 5 AM Monday to 7 PM MST Tuesday for
     UTZ111-112.

     Winter Weather Advisory from 5 PM Monday to 2 PM MST Tuesday for
     UTZ117-125.

WY...Winter Weather Advisory from 7 AM Monday to 2 PM MST Tuesday for
     WYZ021.

&&

Kruse/Cecava/Mahan

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