Heavy Snow in Utah, December 7 to 9, 2023

Area Forecast Discussion
National Weather Service Salt Lake City UT
358 PM MST Wed Dec 6 2023

.SYNOPSIS...A weak system will bring light precipitation to
northern areas tonight, followed by a stronger and colder system
on Friday. Several shortwave troughs are possible through early
next week.

&&

.SHORT TERM (Before 12Z/5AM Saturday)...High pressure will
continue to shift eastward ahead of an approaching trough
currently located along the west coast. Winds at 700-mb will
continue to increase through the overnight hours, peaking around
40-50kts across the area after midnight. Any gusty valley winds
will decrease after sunset as valleys decouple.

The approaching trough will bring light precipitation to northern
Utah overnight, with precipitation peaking along the frontal
passage. Temperatures at 700-mb are likely to drop from +3C to an
ensemble mean of -7C by Thursday morning behind the front. This
first system will also bring a transition to overall westerly
flow. Overall, this system will be lacking in both synoptic dynamics
and moisture availability, with only a few inches of snow
possible across the northern mountains.

After a brief break on Thursday afternoon, another wave within the
main trough will move in...colder and more dynamic than the
first. The associated cold front will begin to move in from the
northwest early Friday morning, with sufficient upper- to mid-
level forcing from a jet streak to our northwest and a vort max
passing through. For the most part, the heaviest precipitation is
expected along this frontal passage. Models are starting to hint
at some additional frontogenesis across northern Utah on Friday
morning, which could produce some heavier snowfall rates.

With 700-mb temperatures dropping to -13C behind the front, snow
is expected down to valley floors. While this latest package has
shifted to slightly lower snow amounts, still expect roughly 1-3"
along the Wasatch Front and Cache Valley, with benches seeing
closer to 4-6". The northern mountains are likely to see around
8-16" with locally higher amounts in excess of 18" in the Upper
Cottonwoods, given favorable northwesterly flow.

This system will certainly focus on northern Utah, however modest
snow accumulations can be expected across the central and southern
mountains (4-8") as well as central valleys, too (1-2").

Areas of uncertainty include the exact timing of the frontal
passage along the Wasatch Front as well as any development of
lake-effect or lake-enhancement. Snowfall will more likely impact
the early portion of the Friday morning commute, though there is
still lingering uncertainty in the exact timing of this band of
heavier snow. Luckily, the band will be fairly short-lived,
however more impacts are possible if the band hits at the wrong
time.

With such a cold air mass and lake temperatures still hovering
near 40F, this could produce sufficient low-level instability for
lake-effect or at least lake-enhancement. Locally heavier snowfall
rates and thus upper-end snowfall amounts could be seen. The
highest lake-effect probabilities (near 35%) are currently in the
Salt Lake Valley during the morning commute, around 7AM-9AM, so
we'll have to keep a close eye on this portion of the forecast.

Snowfall will then continue through the day, gradually tapering
off through the afternoon. Some mountain showers may continue into
the late evening in northwesterly- to northerly-favored areas.
Saturday morning lows will likely be quite cold.

.LONG TERM (After 12Z/5AM Saturday)...Saturday will be a cold day,
as the late week storm system exits and drier conditions build in.
Temperatures at 700 mb are forecast to range from around -14 - -10C
from north to south, which will drop lows Saturday morning into the
teens for many valleys. Lake effect snow chances will be diminishing
through Saturday morning, with less moisture and low 700-500 mb
lapse rates. Isolated snow showers within higher terrain will also
taper off.

An inland-penetrating atmospheric river in the PacNW Saturday will
have a trajectory that will bring enhanced moisture for higher
elevation snow throughout northern Utah Sunday. The main forcing
will be with orographics with west to northwest flow. Snow
accumulations will be light, with the most closer to the Idaho
border where there will be more moisture. Snow accumulations for the
Bear River Range are expected to be roughly 2-5". For other higher
terrain locations in northern Utah, a trace-3" is forecast.

Several shortwaves will track into southwest Wyoming and Utah during
the week. Light precipitation is expected, with snow showers in
higher elevations of northern Utah through Tuesday. Temperatures
will be slightly cooler to near normal from Sunday through
Tuesday.

&&

.AVIATION...KSLC...The SLC terminal will see VFR conditions through
the evening with increasing clouds this evening and overnight.
Prevailing northwest winds are expected to shift to the south
between 03Z and 05Z.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail
through the evening across the airspace. Clouds will increase
beginning this evening over northern Utah with the approach of a
weak storm system. By early morning, pockets of valley rain/mountain
snow will develop, primarily for areas closer to the Utah/Idaho
border, with pockets of MVFR/IFR conditions and mountain
obscurations.

&&

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

SHORT TERM...Cunningham
LONG TERM...Wilson
AVIATION...Traphagan

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