852
FXUS65 KSLC 121122
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
422 AM MST Wed Feb 12 2025

.SYNOPSIS...A cold airmass will settle across the region through
midweek. From Thursday on into the weekend, a moisture rich
atmospheric river type setup will yield significant mountain snow
accumulations across Utah and southwest Wyoming.

&&

.SHORT TERM...Early this morning, Utah and southwest Wyoming are
in cool, northwesterly flow as a longwave trough exits to our
east. With cold temperatures aloft, light lake-effect snow
showers have persisted overnight across mainly the western Salt
Lake Valley and Oquirrh Mountains, with even a few showers over
Utah Valley, too. Accumulations have been light, largely less than
an inch, thanks to the overall lack of moisture in the area.
These light showers will continue intermittently through mid-
morning, with a few mountain showers expected during the afternoon
across northern Utah as a weak shortwave trough sweeps across the
area.

Additionally, temperatures this morning are fairly chilly, around
10-15 degrees below normal. Expect just a few degrees of warming
by tomorrow morning as mid- to high-level clouds stream in
overnight before strong warm-air advection kicks in ahead of the
next storm system.

After a quiet Wednesday night, a shallow mid-level ridge will be
passing overhead Thursday morning, with flow in the low levels
already shifting southwesterly. This marks phase one of the
upcoming storm, defined by strong warm and moist air moving into
the region from the southwest. Precipitation chances will
increase from southwest to northeast through Thursday. The
heaviest period of precipitation is expected Thursday night into
Friday morning given abundant moisture coupled with appreciable
synoptic lift and orographic enhancement. Most valleys will begin
as snow, transitioning to rain by Friday morning below roughly
5000ft across the north and below 6000ft across the south as snow
levels rise. Heavy mountain snow is expected during this period
with flow gradually veering from southwest to west during the day
Friday.

One other aspect to this first phase of the storm is winds. Breezy
southerly to southwesterly winds are expected across the area,
with the highest gusts across western Millard, Beaver, and Iron
counties in southwest Utah. Despite strong 700-mb winds around
45-55kts in this area, winds will have trouble mixing to the
surface given overcast skies and a very moist profile.

As the parent trough axis crosses the area, expect winds to shift
to northwesterly by Friday evening, with precipitation gradually
becoming more orographic in nature with moderate to heavy mountain
snow. Snow levels will gradually fall back down during this
period, returning most valleys back to snow towards the tail end
of the storm Saturday morning.

Now for the biggest question you might have...how much snow can we
expect? Across Utah`s mountains, we can broadly expect 1-2 feet of
snow, with higher amounts likely across favored portions of the
Wasatch and Bear River Mountains. In particular, the Upper
Cottonwoods, which thrive in moist northwest flow, could see in
excess of 3 feet of snow over roughly 3 days. However, one key
piece of uncertainty here is when exactly that flow moves from
westerly to northwesterly, which could influence snow totals. Watches
have been upgraded to Winter Storm Warnings across all mountain
zones given high confidence in significant snow totals, with
Winter Storm Watches remaining in effect for the Wasatch Back and
Bryce Canyon Country given modestly lower confidence.

Regarding valley impacts...the biggest area of uncertainty with
this system is snow levels and how they impact valley
precipitation type. The areas of highest uncertainty are the Ogden
Valley and Wasatch Front benches, as it is unclear for how long
(and if) these areas transition to rain on Friday afternoon and
evening. The current forecast hedges towards lower snow levels and
thus higher snow amounts, though this piece may still change.
Lower elevation valleys such as the Wasatch Front, Cache Valley,
and Sevier Valley will experience minor snow accumulations, mostly
Thursday and early Friday night.

In summary, significant mountain snow is expected state-wide, with
impactful snowfall across higher elevation mountain valleys like
the Wasatch Back. If you plan to travel by road for the holiday
weekend, check road conditions before you leave and consider
adjusting travel plans if needed. Carry a well-equipped emergency
kit if traveling over mountain routes.

.LONG TERM (After 12Z Saturday)...The long term forecast period will
begin with the back edge of the longwave trough associated with a
significant winter storm (discussed in the short term forecast
discussion) exiting the Great Basin. Light snow accumulations are
likely to continue through about sunset Saturday, especially for
mountain locations with preferential orographics.

A brief period of ridging will build into the area, with a period of
associated modest warm air advection. This lull in the active
pattern won`t last long across far northern Utah as the next longwave
trough shifts southward...bringing high elevation snow to the border
region as early as Sunday afternoon. Model consistency is relatively
high for this system, with a majority of solutions (around 80%)
indicating westerly flow associated with a warm air advection regime
bringing accumulating mountain snow as far south as the
Cottonwoods/Provo Canyon by Sunday night.

The biggest question is how far south this trough will dig and how
far south the resulting precipitation will reach. The dominant
solution shifts precipitation as far south as the central mountains
by Monday.  As the main trough moves through the region late Monday
into Tuesday, another, potentially enhanced area of precipitation
will impact portions of Utah (about 65% of the ensemble members).
Current forecast is for 6 to 12 inches or so of additional snow for
the northern mountains (locally up to 18 inches for the upper
Cottonwoods), with 4 to 8 inches for the central mountains.  Will
need to watch trends as warm air advection regimes with westerly
flow can be potent across portions of the northern mountains.

Looking beyond day 7, the active pattern looks to continue.

&&

.AVIATION...KSLC...Winds have been chaotic near light snow showers
this morning, with a south to southwesterly shift becoming the
dominant wind direction. Winds will continue to be chaotic through
around 14Z or so. Any light snow showers will temporarily reduce
visibilities to around 5-6SM at worst. Expect conditions to gradually
improve through the morning, with ceilings above 6000 feet AGL
between 16-18Z.  Additional light snow showers may develop this
afternoon after 19Z, with very temporary reductions in visibility.

.REST OF UTAH AND SOUTHWEST WYOMING...Outside of light snow showers
in portions of Salt Lake and Utah Counties, expect light snow
showers to develop this afternoon across northern Utah. Temporary
reductions to MVFR are likely near these snow showers. Conditions
will improve near sunset.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Watch from Thursday morning through Saturday
     afternoon for UTZ108.

     Winter Storm Warning from 11 AM Thursday to 5 PM MST Saturday
     for UTZ110>113-117.

     Winter Storm Warning from 11 AM Thursday to 11 PM MST Friday for
     UTZ125.

     Winter Storm Watch from Thursday morning through Friday evening
     for UTZ127.

WY...None.
&&

$$

Cunningham/Kruse

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