Winter Storm in Utah, January 5 to 6, 2022

Area Forecast Discussion
National Weather Service Salt Lake City UT
349 PM MST Tue Jan 4 2022

.SYNOPSIS...After a relative lull in precipitation this evening,
the second in a series of troughs will impact northern Utah and
southwest Wyoming early Wednesday into Thursday. High pressure
will briefly return early Friday before the next storm system
impacts the area Friday night into Saturday.

&&

.SHORT TERM (Through 12Z Friday)...Active weather is in full
force, at least for the northern half of the forecast area. The
first of two storm systems to move through the area grazed
northern Utah this morning and precipitation continues, with best
coverage over the higher terrain of northern Utah, across much of
the area this afternoon with jet support remaining favorable with
a good amount of moisture in place. Strong winds this morning
have died down a bit but observations still indicate many wind
gusts in excess of 40 mph at the ridgetops. In between storm
systems, the area should see a relative lull in precipitation this
evening, though some snow will linger over the higher terrain.

The second and stronger wave will make its way into northern Utah
early Wednesday morning, resulting in a long period of heavy snow
for the higher terrain of the northern half of Utah through
Wednesday morning and into Wednesday afternoon. Strong winds will
also redevelop for the northern Utah mountains, the Bear River
Valley, and southwest Wyoming Wednesday morning with gusts in
excess of 50 mph causing areas of blowing snow that will result in
occasional whiteout conditions. Given the very heavy mountain snow
anticipated over northern Utah and the dangerous conditions in
blowing snow for the Bear River Valley and southwest Wyoming, have
upgraded these areas to a Winter Storm Warning and extended the
time of the headline through Thursday afternoon, as snow is likely
to continue through that time. Have also added the Wasatch
Plateau/Book Cliffs and the Central Mountains to the Winter
Weather Advisory given the anticipated amounts and impacts.

There is a bit more uncertainty with regard to some valley impacts
due to precipitation type. For valley locations near the Idaho
border such as the Cache Valley, precipitation type should be all
snow, resulting in enough accumulation to result in travel
difficulties, particularly during the Wednesday morning commute.
As one goes farther south into the Wasatch Front, there is greater
potential of rain, particularly for the lower valleys. Some snow
could impact the morning commute from about Ogden northward as
well as in bench locations, but the lower valleys of Salt Lake
City and Provo will likely see rain at this time. Precipitation
will continue throughout the day and into the evening, starting to
taper off late evening into the overnight hours. However, snow
will continue for the northern Utah mountains, southwest Wyoming,
and areas near the Idaho border through much of the day Thursday
as moisture and instability linger.

Across southern Utah, impacts from this stormy period will be
limited to some periods of increasing winds and perhaps some
clouds. Temperatures will be on the mild side, running 5-10F above
seasonal normals.

.LONG TERM (After 12Z Friday)...The long-term forecast period
begins with overall zonal flow at the mid levels under a flattened
ridge. Flow is then expected to shift to southwesterly overnight
Friday ahead of an approaching trough. This trough will bring
minimal precipitation impacts, with storm-total QPF remaining around
a half inch in the central and northern mountains and closer to a
quarter inch in the adjacent valleys. Following this trough, a ridge
builds in for the rest of the forecast period, with the potential
for an inversion and valley air quality concerns.

Just ahead of this approaching trough, vorticity advection along
with favorable upper-level jet support may bring some mountain
showers to northern Utah starting 18z Friday. After 00z Saturday,
these PoPs will likely fill into the valleys of northern Utah, where
precipitation will begin as rain below 6000 feet early Saturday
morning when QPF is highest, however with high precipitation rates,
there could be an earlier transition to snowfall, which may result
in higher valley accumulations. In general, rain in the valleys is
expected to switch over to snow between 12-18z Saturday with the
passage of a cold front, however QPF near this period is expected to
remain minimal.

After 18z Saturday, PoPs across the CWA diminish under a building
ridge, which will also increase temperatures overhead, however
minimal warming trends are expected in valley areas as inversion
conditions are anticipated to exist. The region appears to remain
under this ridge through the end of the forecast period, which may
produce an inversion, especially if valleys see recent snowfall with
this upcoming trough.

&&

.AVIATION....AVIATION...KSLC...TAF forecast expected to be VFR through
approx 08Z with snow showers in the vicinity. Lower layer broken or
overcast ceilings around 4,000 feet are possible until this time,
however. After 08Z, variances in the timing in the arrival of a
rain/snow band exists between short term forecast models, which is
making the TAF forecast difficult. Several short term models
indicate a band of snow will arrive at SLC between 08Z and 11Z
while the NBM forecast waits until the early morning hours, around
15Z, before MVFR conditions arrive. There is also a question as
to precipitation type, rain versus snow, but it is likely at this
time to be a mixture of the two. In addition, there is also a
chance for LLWS for a few hours in the very early morning hours as
well which would improve by approx 15Z. Models are currently
showing a brief break in rain/snow late morning. However, MVFR
ceilings would persist. The next band of rain/snow is expected to
arrive early afternoon and would persist into the evening.
Ceilings and visibilities may drop to IFR during this period.

REST OF UTAH AND SOUTHWEST WYOMING...Bands of snow will bring
periods of lowered CIG and VIS for several northern UT locations
while those not under a band will see VFR conditions. Variances in
the short term forecast models are making forecasting difficult
to time out exactly when to reduce VIS and CIG. That said, MVFR
conditions are most likely in far northern UT locations in the
late evening hours, during the overnight hours across Wasatch
locations and by the early morning hours in the central valleys.
In addition, LGU is likely to see IFR and potentially LIFR
conditions beginning late this evening. LLWS is possible during
the overnight and early morning hours across western and northern
UT locations as well as EVW. This threat should diminish mid-
morning. Southern Utah locations are expected to see breezy
conditions at times but will remain VFR throughout the forecast
period.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 5 AM MST Thursday for UTZ107-108.

     Winter Weather Advisory from 11 PM this evening to 5 AM MST
     Thursday for UTZ113-117.

     Winter Storm Warning until 5 PM MST Thursday for UTZ109>112.

WY...Winter Storm Warning until 5 PM MST Thursday for WYZ021.

&&

SHORT TERM...Traphagan
LONG TERM...Cunningham/Webber
AVIATION...NDeSmet

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