Avalanche in Utah, January 23, 2025

Area Forecast Discussion
National Weather Service Salt Lake City UT
337 AM MST Thu Jan 23 2025

.SYNOPSIS...High pressure will bring dry conditions to Utah and
southwest Wyoming through Friday, with increasingly mild
temperatures on Friday. A low pressure system moving into the
Great Basin will bring unsettled conditions for Utah and southwest
Wyoming for the weekend and early next week.

&&

.SHORT TERM (Through 12Z/5AM Saturday)...High pressure is centered
near the California coast this morning, with Utah and southwest
Wyoming under dry northerly flow out ahead of it. A trough moving
across Colorado on the front side of the ridge is bringing some
cloud cover to eastern Utah, with mostly clear skies elsewhere.
Impacts over the area will be limited to some enhanced gap winds
for prone areas of Washington county and enough cooling to curb
any warming trend across the area.

By Friday, as the ridge starts to flatten and move south in
response to a Pacific Northwest trough moving onshore, the flow
aloft will become zonal, increasing warm advection into the area.
As a result, temperatures will be noticeably more mild, with maxes
running up to 5F above seasonal normals. Clouds will be on the
increase late Friday as the previously mentioned storm system
dives south into the Great Basin while closing off. This will
bring a long period of unsettled weather over the weekend and
early next week that is discussed further in the long term portion
of the discussion.

.LONG TERM (After 12Z/5AM Saturday)...Key takeaways for the long-
term forecast are as follows:

* Light snowfall is expected this weekend across the forecast area,
  lasting into next week across southern Utah. Daily accumulations
  will be relatively minor. Lower Washington county may even see
  minor snow accumulations with around a 10-20% chance of >1".

* There is still a decent amount of spread in the snowfall forecast
  across the area...especially for southern Utah due to
  uncertainties with how late into next week snow persists.

* Enhanced canyon winds are appearing more likely on Saturday across
  the Wasatch Front/Cache Valley near canyon mouths, with still a
  low chance of stronger downslope winds developing.

At the start of the long-term period on Saturday morning, a ridge
pushing into the PacNW will act to pinch off a closed low over
roughly NorCal/NW-NV, leaving Utah in overall westerly to
southwesterly mid-level flow. If we take a look lower in the
atmosphere, however, we can see that 700-mb heights will likely have
closed off (sooner than at 500-mb) by early Saturday, resulting in
easterly low-level flow and cold-air advection across northern Utah.
This flow luckily does not appear to be terribly strong, maybe 20-
30kts at 700-mb for a short period of time during the day, thus will
likely just result in enhanced canyon winds along the northern
Wasatch Front and Cache Valley. There is an outside chance that
stronger downslope winds occur, though it is difficult to discern
without higher resolution guidance, and the chance remains fairly
low at this time. One concern is the potential development of a
critical layer (flow reversal) above ridgelines given mid-level
westerly/southwesterly flow and low-level easterlies...though again,
difficult to discern at this time.

As far as precipitation goes, light snow will likely already be
occurring Saturday morning across northern Utah, gradually shifting
southward across southern Utah heading into Sunday as the low to our
west nudges southward. More moisture wrapping around from the
southwest will aid snowfall Sunday night into Monday across southern
Utah, though both moisture and dynamics aren't that impressive as a
whole with this system, at least across Utah. Thus, accumulations
will remain fairly low outside of areas of a orographic enhancement
(mainly the Brian Head area). Even there, model spread is still
fairly high, with a 25th-75th percentile spread of 1-10" of snow (3-
9" for the Upper Cottonwoods for comparison). Given the cold air
mass overhead, even St. George has a 10-20% chance of 1" of snow on
Sunday-Monday.

With some model spread with how quickly the low progresses eastward
across AZ early in the work week, there is some uncertainty with how
long this light precipitation lasts across southern Utah...perhaps
as late as Tuesday or Wednesday...or if you believe the Canadian,
into Thursday. Ridging will then begin to nudge into Utah later in
the work week, bringing a slight warming trend to the area.

&&

.AVIATION...KSLC...Light and variable winds will continue through
much of the morning, potentially becoming northwesterly after 19z.
Winds could remain light and variable through the day without that
northwest wind shift (40% chance). VFR conditions and clear skies
will prevail.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will
prevail through the valid TAF period at most terminals. Fog may
develop early this morning (13-17z) near KLGU, moving over the
terminal intermittently (40% chance of LIFR conditions). Light,
terrain-driven winds will persist across most areas, the exception
being northerly winds at 10-15kts across SW-UT this afternoon
(mainly KCDC and KBCE).

&&

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

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

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