Sandy, Utah 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

554
FXUS65 KSLC 231118
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
418 AM MST Sat Nov 23 2024

.SYNOPSIS...A dry and mild southwesterly flow will reside across
the area today ahead of an approaching cold front. This front
will cross northern Utah tonight into early Sunday, before
continuing into central and southern Utah during the day Sunday.
High pressure will bring a temporary drying trend Monday, before
another storm system impacts the region midweek.

&&

.SHORT TERM (Through 12Z/5AM Monday)...Enhanced southwesterly flow
resides across the eastern Great Basin this morning, downstream
from an upper trough and remnant atmospheric river making landfall
along the California coast. Thus far this elevated flow aloft has
primarily impacted upper ridgelines, however as the morning
progresses will begin to see a response across western valleys, in
particular southwest and perhaps portions of west central Utah.
Have maintained going Wind Advisory for southwest Utah including
Cedar City and Milford throughout the day, but held off on
expanding this northward and stronger flow looks to mainly impact
higher elevations of western Millard County. Will need to keep an
eye on winds across west central Utah however, as well as further
east across the Sevier Valley. The airmass within this
southwesterly flow remains mild, and while increasing cloud cover
today will result in an overall cooling trend, temperatures will
continue to run nearly 10F above normal across most valleys.

A shortwave trough crossing the northern Rockies today will push a
predominantly dry cold front into northern Utah this afternoon.
This boundary will stall in advance of an upstream wave, which
will translate across the Great Basin overnight through Sunday. As
this upstream wave interacts with the stalled boundary,
frontogenesis will result in the development of a band of
precipitation beginning mid-evening, then strengthening overnight
into Sunday morning across the central and southern Wasatch front,
adjacent terrain, and into far southwest Wyoming. Eventually this
band will spread into central Utah, weakening with time during
the day Sunday as the upper forcing begins to move away from the
area. By late Sunday afternoon anticipate any lingering snowfall
to have largely ended across the forecast area.

Overall not much change in the overall thinking regarding the
evolution of the frontal band tonight through Sunday, with precip
largely remaining confined to the baroclinic zone. As with any
developmental system and banded precipitation, until it shows
itself some uncertainty will remain regarding exact placement
during the developmental phase this evening, as well as forward
speed overnight through SUnday morning, with some concern this
band may have a longer residence time cross the central/southern
Wasatch Front eastward into southwest Wyoming, which would
increase precip/snow totals in these areas. It does look like snow
levels will reach the valley floors overnight through Sunday
morning across the Tooele/Salt Lake/Utah Valleys. As of now any
valley snow accumulation looks minimal with the greatest
probability for accumulating snowfall coming across Utah Valley.
However an earlier transition and/or longer residence time within
the frontal zone could result in more appreciable valley
accumulation. Mountain snow totals remain largely unchanged from
the previous forecast, and going Winter Weather Advisory for these
areas looks in good shape. May need to expand this advisory into
Uinta County and perhaps the Wasatch Back for later tonight into
Sunday morning, but for now have held off to allow for an
opportunity to collaborate with partners.

.LONG TERM (After 12Z/5AM Monday)...Several days of active weather
are expected leading into the Thanksgiving holiday. Pre-Thanksgiving
travel over mountain passes and through mountain valleys will almost
certainly be impacted by snow, while valleys are likely to start as
rain before transitioning towards snow by Wednesday.

Transient shortwave ridging Monday will support a brief break in the
action early Monday before a decaying atmospheric river approaches
southern Utah ahead of the next Pacific NW trough moving onshore.
Ensembles are now in good agreement in depicting southwesterly flow
aloft through next Tuesday, followed by the trough moving inland
towards midweek. The main uncertainty is how quickly the trough
progresses inland as well as how much cold air it brings with it.
Either way, ahead of the trough, Atmospheric River analysis tools
suggest that the southwesterly trajectory will bring the potential
for significant moisture arriving around the southern end of the
Sierra Nevada into the Desert Southwest and eventually spreading
through the eastern Great Basin and all of our area by Tuesday.
Specifically, the latest global ensembles indicate a 60+% chance of
an inland-penetrating AR reaching southern Utah Tuesday. While the
flow will not be as strong elsewhere in the forecast area to reach
the AR defined threshold (250 kg/m/s), plenty of moisture is on tap
throughout the remainder of Utah and southwest Wyoming. This
moisture tap looks to last until the trough pushes through, which
looks to be as early as Wednesday or as late as Thanksgiving per
ensembles, resulting in a 48-72 hour potential period of
precipitation.

Current NBM ranges for liquid equivalent in a 48 hour period are
generally in the half inch to inch range for valleys and 0.75"-2"
range for mountains. The lower-end outcomes reflect less moisture
transport around the southern Sierra into our area as well as a
quicker trough passage, and visa-versa for the higher end scenario.
Ensemble 700MB temperatures initially warm to -2 to -5C in the warm
sector mid-day Tuesday, dropping to -7 to -11C Wednesday (warmest
over southern Utah in both cases). This translates to initial snow
levels of 8kft in the south to 6-7kft in the north dropping to
around valley floors Wednesday/Thursday, though there is still
uncertainty whether they will fully reach the floors. Translating
all this to snow potential, it is highly likely that most mountains
will exceed a foot of wet snow (easily so in areas favored by the
southwest flow). Probabilities for other elevations are generally
low and difficult to interpret given the temperature/timing
uncertainties, but should come into focus in the coming days.
Lastly, it should be noted that the current deterministic forecast
from our office represents the lower end of the probabilistic liquid
spectrum mentioned earlier.

After the trough progress through the region, cold temperatures will
linger in its wake for around Thanksgiving onward. Looking ahead to
the end of November and early December, ensemble systems (esp the
Euro) favor a period of dry conditions with a building West Coast
ridge. This brings the concern of valley inversions developing. The
specifics of where that ridge develops will impact whether we
receive any beneficial shortwave troughs to increase mixing or
experience a prolonged period of stagnant conditions.


&&

.AVIATION...KSLC...VFR conditions will continue through today before
deteriorating tonight as a cold front pushes through the area. The
front will bring a wind shift along with rain changing to snow
overnight and lower ceilings (60% chance of MVFR cigs by 6Z). Ahead
of the front, very strong southwesterly winds up to 40kts at around
2000ft AGL will continue this morning through at least 18Z. At the
surface, southeast winds will be lighter through the same period,
with occasional gusts up to 25kts as stronger winds aloft
intermittently mix to the surface. This difference in direction and
speed will result in impactful wind shear, again through around 18Z
before gradually decreasing. Surface winds will abruptly switch to
northwesterly as the surface front pushes through, somewhere between
20 and 02Z, currently most likely to arrive at 23Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Increasing southerly flow is
in store for the region today, along with increasing clouds, as a
cold front approaches the area. Southwest winds at several thousand
feet AGL will top 40 kts this morning, especially along a line from
KCDC to KEVW including the I-15 corridor. Meanwhile, these winds
will only occasionally mix to the surface, leading to potential wind
shear concerns. Lighter northwest winds will accompany the front as
it moves into northern Utah after sunset and tracks through central
Utah through tomorrow night. Behind the front, a band of moderate
precipitation with snow levels crashing to valley floors is expected
over northern Utah overnight, leading to likely MVFR conditions from
KPVU to KOGD. &&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
     Sunday for UTZ110>113-117.

     Wind Advisory until 5 PM MST this afternoon for UTZ122.

WY...None.
&&

$$

Seaman/Van Cleave

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