409
FXUS65 KSLC 242241
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
341 PM MST Sun Nov 24 2024

.SYNOPSIS...High pressure will bring a temporary drying trend
tonight into the day Monday, before a moisture-rich storm system
makes its way across the area late Monday through Wednesday. The
ridge will return for Thanksgiving Day and beyond.

&&

.SHORT TERM (Through 12Z/5AM Tuesday)...A Pacific Northwest storm
system is on its way out this afternoon, as shortwave ridging
makes its way back over Utah and southwest Wyoming. Some
precipitation persists along the frontal band located over
southern Utah, but it has weakened significantly after becoming
removed from the main system. A few showers persist over northern
Utah, but all of this will continue to diminish late this
afternoon and early this evening. Canceled the going winter
weather headlines over southwest Wyoming and the mountains of
northern Utah around midday as the precipitation diminished.

The ridge will shift itself east of the area by tomorrow afternoon
as another storm system moves onshore along the Pacific northwest
coast. To the south of this feature, confidence is increasing that
a decaying atmospheric river will makes its way into southwest
Utah, potentially as early as Monday afternoon, bringing the start
of another round of mountain snow and valley rain. This deep
moisture will spread northward across the remainder of the
forecast area Monday night into Tuesday morning. The evolution of
this system will be discussed further in the long term section.

.LONG TERM (After 12Z/5AM Tuesday)...A moisture-rich storm system
will impact Utah and southwest Wyoming in the days preceding
Thanksgiving, with an extended period of heavy, wet mountain snow
and plentiful valley rain. Those with travel plans ahead of the
holiday over mountain passes should be prepared for potential travel
difficulties, particularly Tuesday through Wednesday morning.

Broad southwesterly to westerly flow will be in place to start on
Tuesday morning, with deep column moisture across the entire
forecast area, thanks to a decaying atmospheric river. This pre-
frontal environment will be supportive of plenty of valley rain and
orographic enhancement across areas that do well in southwesterly
flow, such as the vicinity of Provo Canyon. Snow levels will be
fairly high to start, around 7000-8000ft.

In addition to this high moisture availability, a low will swing
down from Oregon on Tuesday, providing more upper- to mid-level
dynamics and a surface cold front. This frontal passage, likely to
cross the state between Tuesday night and Wednesday morning, will
bring a period of heavy precipitation, lower snow levels, and a
transition to northwesterly flow. There is still some uncertainty
with how quickly this low moves through, and thus how long
precipitation will last on Wednesday. Some models favor low-level
moisture hanging on for a bit longer with a slower low, though this
is split roughly 50-50 with a faster solution that brings a drier
air mass in more quickly behind the storm system.

Another area of uncertainty is spatial distribution of QPF across
the area. There is a balance between the best moisture to the south
and best dynamics to the north, with some question to where exactly
the trough moves through. A lot of model guidance is still focusing
on areas between the central Wasatch down to the Manti Skyline,
though even areas over the southern mountains could do quite well,
too. The EC Extreme Forecast Index (EFI) is even moreso highlighting
the central mountains than yesterday, indicating abnormally high QPF
and snowfall. Currently, model guidance suggests broadly 0.5-1" QPF
for most valleys, with 1-2" QPF for the mountains (locally higher up
to 2.5" for portions of the central/southern Wasatch, Manti Skyline,
and Tushars). Winter Storm Watches have been issued for all mountain
zones, with even a low (15%) chance of up to 3 feet of snow possible
for the aforementioned locations receiving the highest QPF.

As far as valley snow accumulations go, while 700-mb temperatures
are expected to drop to around -9C to -11C across northern UT behind
the front, much of the precipitation will fall ahead of the frontal
passage...thus only minor accumulations are expected across most
valley locations. The Wasatch Back and Uinta Co., WY are likely to
transition earlier, being at higher elevations, thus could see up to
a few inches of snow.

Finally, after this storm system makes its way eastward, a west
coast ridge is likely to develop on Thursday, resulting in
persistent dry, northwesterly flow. While this will be a largely
subsident regime, a couple of weak shortwaves may keep valleys mixed
enough to hopefully ward off inversion development. A weak closed
low crossing AZ may produce some light precipitation across southern
UT on this weekend, but the weather will overall remain quiet
through the weekend.

&&

.AVIATION...KSLC...Clouds will diminish, with mostly clear
conditions by around 03Z. Northwest winds will transition to
southeast around 03Z. Light southeast winds with mostly clear
conditions will last through around 19Z. Clouds will increase with
south winds prevailing from 19Z through the evening.

.REST OF UTAH AND SOUTHWEST WYOMING...Clouds will diminish, with
mostly clear conditions by around 03Z for southwest Wyoming and much
of Utah. Clouds will increase throughout southern Utah by around 09Z
as a storm system tracks in from the west. Clouds will build
northward through the day. Dry conditions are likely much of the
day, with rain showers tracking into southwest Utah around 19Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Watch from Monday afternoon through Wednesday
     afternoon for UTZ110>113-117-125.

WY...None.
&&

$$

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

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