434
FXUS65 KSLC 101122
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
422 AM MST Fri Jan 10 2025

.SYNOPSIS...A storm system pushes into Utah late today, bringing a
period of accumulating snowfall from Friday night through early
Sunday. Minor valley snow accumulations are expected to bring
minimal impacts, however, higher elevation transportation routes
through the mountains will see at least some impact. Cooler and
drier conditions persist through much of next week, with
increasing chances for precipitation late in the week.

&&

.SHORT TERM (Through 00Z Monday/ 5PM Sunday)...

Key Messages:

* Minor valley snow accumulations in northern and central Utah
  are expected late Friday night through Saturday.

* Northern Utah mountains will see a period of snowfall from
  Friday evening through at least Sunday morning, bringing minor
  impacts to the high elevation transportation routes (upper
  Cottonwoods, Parley`s Summit, US-89 Bear Lake Summit, Sardine
  Summit).

* There is a low probability (15% or less) of a lake effect band
  setting up, which would bring an additional 1-4 inches of
  snowfall to the Salt Lake Valley Saturday evening through Sunday
  morning.


A brief period of shortwave ridging eclipses Utah and southwest
Wyoming today, bringing warming temperatures overhead during the
afternoon and generally stable conditions. As a result, we`ll see
a slight warming trend across Utah`s western valley areas. Areas
in eastern Utah are expected to have a longer residence time in
the departing colder airmass, so expecting little to no warming in
this region. The axis of the mid-level shortwave ridge shifts
eastward later this afternoon, opening the door to our next storm
system.

As the ridge axis shift east through the late afternoon and
evening hours, the aforementioned warming temperatures in the
lower levels will be shunted eastward as well. A transition to
northwesterly flow will introduce gradually cooling temperatures
overhead as well as a period of moisture advection ahead of the
primary frontal boundary tied to an approaching trough. As such,
the chance for higher elevation snowfall in the northern Utah
mountains will increase gradually through the evening hours
today. Not expecting much in the way of impacts with this initial
moisture push, but enough to get the high elevations primed for
the primary baroclinic zone.

A more stout low-level frontal boundary will push into northern
Utah late this evening and into Saturday morning, accompanied by a
higher concentration of lower and mid-level moisture. The
combination of these two features will be the main driving force
behind the initial shot of snowfall for both valley and mountains
across northern Utah. Current high-res and synoptic models show
the best potential for snowfall across northern Utah between
midnight and 5AM, with a majority of the accumulations from this
system expected through this period. For the valley areas, the
most likely snow accumulations will range from 0.5-1.5 inches for
the central/ northern Wasatch Front and Cache Valley, 2-4 inches
on the Wasatch Back (locally up to 6" in the Park City area), and
generally 0.5 inches or less for the southern Wasatch Front,
central Utah valleys, and Uinta County, WY. For the mountains of
northern and central Utah, a widespread 3-6 inches is expected
for areas favored in northwesterly flow (i.e. Wasatch Mountains,
northern Bear Rivers, western Uintas, and the Manti Skyline).

After 5AM, overhead instability increases, however, the mid-level
moisture will be on a decreasing trend. Thinking that in this
post-frontal environment the mountains, and adjacent downstream
valleys, will the most favored. With temperatures plummeting
behind the front, additional snowfall will be low density and
stack up easily. When all is said and done (by Sunday evening), we
should see a widespread 3-8 inches for the northern Utah
mountains, with locally upwards of 16 inches in the upper
Cottonwoods.

There is a low probability (~15% or less) that a lake effect band
develops in the wake of the cold front on Saturday afternoon
through Sunday morning, which could help to provide impactful
additional snow accumulations for both mountains and valleys. For
the Salt Lake/ eastern Tooele valley areas, 90th percentile
accumulations during this period accumulate anywhere from 1 to 4
inches through Sunday morning. Though unlikely, this could stir up
some trouble for drivers in these areas.

Given the timing of when all of this is to unfold and impacts
limited to the higher elevation routes of the Wasatch, have
decided to not issue any headlines yet. Will allow the day shift
to coordinate with core partners to increase messaging.

.LONG TERM (After 00Z Monday/5PM Sunday)... Cool and dry
condition will prevail across the forecast area through much of
next week. Initially northerly flow aloft will reside across the
region Sunday, but will quickly transition to an upstream Rex
Block along the Pacific Coast Monday through Wednesday, with the
upper low parked off the southern California coast, and the upper
ridge encompassing much of the Pacific Northwest, northern Rockies
and Great Basin region. This upper low should remain far enough
upstream that easterly flow across the forecast area should not be
a problem, but it is something to be watched during the
developmental phase of this upstream blocking pattern Monday.

Temperatures early in the week will run roughly 5 degrees below
climo across northern valleys, and nearly 10F below climo across the
south, struggling to reach the freezing mark across most western
valleys including the Wasatch Front. As the upper ridge builds into
the region early in the week, warming aloft will be realized across
higher elevations along with much of southwest Utah, however
northern/central valleys will become inverted with a very slow
warming trend. As such have trended temps across inversion prone
areas toward the 10th percentile of max temp guidance.

Late in the week the upstream blocking pattern begins to break down,
and as is typical in these scenarios considerable uncertainty exists
regarding the evolution of the upstream low, as well as any
influence from northern stream shortwaves. As such PoPs trend upward
toward the end of the week, however at this point no significant
storm systems appear likely for the latter portion of the extended
and into the following weekend.

&&

.AVIATION...KSLC...Southerly winds with VFR conditions will prevail
through the day today. CIGS will gradually lower after 03Z tonight,
with a cold frontal passage between 08-09Z shifting winds to the
northwest. Periods of MVFR CIGS/VIS withing light snow will follow
during the 09-15Z timeframe, with a 40% chance of IFR conditions
during this time. An snow accumulation at the airport will remain
less than 2 inches on untreated surfaces overnight through Saturday
morning.

.REST OF UTAH AND SOUTHWEST WYOMING...Patchy stratus will bring low
end VFR CIGS around PVU and HCR through 15Z, and there is a 20%
chance for fog at LGU through 17Z. Otherwise VFR conditions will
prevail through this evening. Ceilings will lower this evening after
00Z across northern Utah/southwest Wyoming terminals, with periods
of MVFR to IFR snow spreading across these areas generally after
06Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

SHORT TERM...Webber
LONG TERM...Seaman
AVIATION...Seaman

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