219
FXUS65 KSLC 191117
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
417 AM MST Sun Jan 19 2025

.SYNOPSIS...A weak weather disturbance will bring light mountain
snow Sunday and Monday and another shot of cold air, with some
locations likely to reach their coldest readings since 2023. A
gradual warmup is then expected for the back half of the work
week, followed by a potential weekend storm.

&&

.SHORT TERM (Through 12Z/5AM Tuesday)...Early morning water vapor
imagery shows broad northwest flow across the Intermountain West,
while the Nighttime Microphysics product shows lingering mid-
level clouds in the higher terrain around I-80 northward with
higher clouds quickly dropping into northern Utah. Area radars
show light returns with this higher clouds along the UT/ID border,
though this activity is elevated as of this writing. With
clearing most of the night up until the arrival of the aforementioned
higher clouds, temperatures have dropped to widespread teens and
single digits. Of note, the SLC ASOS has reached the upper teens
(19) for the first time this season, which is actually the latest
date on record (demonstrating the overall warmth this winter
compared to normal).

A weak shortwave trough will slide southeastward through northwest
flow later today into tonight. The main effect for most areas will
be cloudy conditions today, with a few snow showers over the
higher elevations (mainly east of I-15). Despite very little
moisture, snow showers should be efficient at squeezing out
fluffy flakes with snow-to-liquid ratios approaching 20-to-1. The
current forecast has very little snow accumulations (largely
driven by high-res models which have turned almost entirely dry
expect over the north slopes of the Uintas). But, it is worth
noting that high-res models have struggled with these low-density
snow setups recently, so would not be surprised to see some
localized over-performance, especially in any areas favored in
northwest flow such as the Cottonwood Canyons. While unlikely
given dry air at the surface, there is a low chance (~20%) of
flurries reaching valley floors as well.

The coldest air yet this season is expected to arrive Monday
behind the weak shortwave trough mentioned above. Current HREF
700MB temps over northern Utah are running -18 to -20C.
Consequently, highs Monday will be brisk, some 10 to 20 degrees
below normal. If SLC`s forecast high on Monday of 26 were to
verify, it would be the coldest high temperature since the
2022-2023 winter (one in which we had much more snow cover).
Comparing to our Extreme Cold Warning criteria, apparent
temperatures (i.e. wind chills) are generally not being reached
in the main population corridors and more sensitive rec areas such
as Zion NP and Lake Powell Monday night into Tuesday morning, but
they are close, especially considering forecast uncertainties
with wind gusts. Future shifts will need to keep an eye in case we
reach enough confidence to issue highlights for this hazard. You
would certainly not want to break down on I-84 near Snowville
Monday morning, for example, where current wind chills are
forecast to dip into the negative teens.

Lastly, such a cold air mass will set up brisk northerly winds
Monday as well as windy conditions for north-south canyons of
Washington County through early Tuesday. Local gap wind tools
suggest that gusts will be mostly below advisory criteria, though
it is worth noting that the latest NBM guidance has ticked upward
and is now touching advisory levels in isolated areas (e.g. along
I-15 between St George and Cedar City).

.LONG TERM (After 12Z/5AM Tuesday)...High pressure across the
eastern Pacific and an anomalously deep trough across the central
and eastern CONUS will keep the Intermountain West locked into a
northerly flow regime that will result in some of the coldest
temperatures we have seen in a couple of years across the CWA on
Tuesday morning. Light winds and mostly clear skies overnight
Monday will promote efficient radiational cooling leading to
plummeting overnight lows. Temperatures will be in the single
digits to below 0 for most locations with teens across Lower
Washington county and the Lake Powell area. To put things into
perspective, our forecast low for KSLC Tuesday morning is 11F. The
last time we were this cold was January 30, 2023 when 9F was
recorded. This cold will be dangerous for unsheltered populations
as well as pets that are exposed to the elements.

The airmass responsible for the cold air will also be very dry owing
to its continental origin. No ensemble members have any sort of
precipitation until next weekend when our next trough arrives that
will potentially bring some moisture back to the area (more on that
in a moment). Temperatures will gradually increase throughout the
week as the aforementioned trough shifts further east and the ridge
to our west nudges slightly closer to us. This will lead to
temperatures aloft and at the surface increasing closer to
climatological normal by the end of the week.

The next trough arrives some time next weekend. There is good
agreement amongst ensemble members about the arrival of the trough,
but there is a lot of uncertainty regarding the impacts and moisture
content of the trough. Right now there are 2 scenarios that are
almost split 50/50. The first scenario (52% of members) brings a
deep trough into the Great Basin with ample moisture for widespread
precipitation. The second scenario (48% of members) brings either a
splitting trough or more of a grazing weak trough that is much
drier. The highest confidence remains in the temperature aspect of
the trough. It will bring another dose of colder air that will drop
temperatures back down to near or below normal for this time of year.

&&

.AVIATION...KSLC...VFR conditions will persist for the KSLC terminal
through the period. A cold and dry airmass in place will deliver
only a few mid and high level clouds. Otherwise, winds will be light
and diurnally driven.


.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist
for the entire airspace through the period. A cold and dry airmass
in place will deliver only a few mid and high levels clouds across
the northern airspace with clear skies to the south. Otherwise,
winds will be light and variable areawide.

&&

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

$$

SHORT TERM...Van Cleave
LONG TERM...Mahan
AVIATION...Mahan

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