Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 212226
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
426 PM MDT Thu Mar 21 2024

.SYNOPSIS...The arrival of the next longwave trough Friday night
will kick off an extended period of active weather expected to
continue through next week. Initial impacts from a strong cold
front Saturday afternoon include widespread mountain snow, and
strong wind gusts.

&&

.SHORT TERM (Through 12Z Sunday)...A weak shortwave centered over
Utah this afternoon continues to produce weakly banded showers
across central and southern Utah, with occasional lightning
observed in some of the better developed cells. With significant
dry air in place and more of a spring-like inverted-V sounding
modeled across southern valleys, some showers will also be capable
of producing strong wind gusts, with 57 mph the strongest
observed so far.

This feature will shift eastward overnight, giving way to short-
lived transient ridging to start the day on Friday. Moisture
spilling over the top of the ridge will prevent totally calm and
clear weather, though little in the way of active weather is
expected until late at night on Friday into the early morning
hours Saturday. Models are in good agreement that this feature
will be quite frontogenetic as it shifts from eastern Nevada into
northwestern Utah. Warming on southwesterly flow and under
increasingly strong springtime sun will also aid in enhancing the
low-level temperature gradient beyond that developing aloft at
700 mb.

Uncertainty in timing of arrival of the front, strong winds, and
associated precipitation remains, with the majority of the
ensemble forecast members clustering around this feature
progressing through northwestern Utah 2-5PM Saturday. Some areas
could see wind speeds increase above 45 mph by 9AM, and lasting
through as late as 9PM. For peak gusts, a 55-60% chance exists
that areas of the central and southern West Desert will see wind
gusts 58-65 mph. Lower confidence exists in these peak wind gusts
in the northwestern corner of Utah, as some uncertainty remains in
the intensity of the front through that area.

While rapid cooling with the front will drive snow levels down in
its wake, daytime highs on Saturday will be tough to overcome in
terms of accumulating snowfall. While snow may mix in down to
valley floors, this will largely be a mountain snowfall event.

.LONG TERM (After 12Z Sunday)...Long term period begins in a
post-frontal environment as the base of a deep and cold trough
begins to settle into the forecast region. Modest synoptic support
along with lingering moisture will yield continued elevated
precipitation chances, with best SWE/rates ongoing at higher
terrain. Still, the cold core of the trough characterized by H7
temps around -6C to -9C will promote mean snow levels initially
~4500-5000 ft. As a result, could see some lower elevation valley
snow showers Sunday morning, especially in any local areas seeing
some further lowering as a result of precipitation rate driven
cooling. That said, potential for low elevation snow accumulation
looks pretty minimal, with even benches only showing around a
10-20% chance of picking up a trace or so. Snow levels will
increase as the day progresses, with snow becoming further
constrained to high terrain. While coverage will be dependent to a
degree on how many breaks can develop in the cloud cover,
ensemble mean instability increases to ~50-100 J/kg by Sunday
afternoon with the trough settling in overhead, so expect an
uptick in shower activity accordingly. Given the cold temps aloft,
wouldn`t be too surprised to see a little graupel in some of
those convective showers as well. With the cold airmass, afternoon
highs will run roughly 5 to 15 degrees below climatological
normal.

Moving into Monday, the deep trough continues to exert its influence
over the local forecast region, while the trough axis itself begins
to shift east. With the cold air, GFS derived lake effect guidance
highlights a low (~10%) chance of some lake effect/enhanced showers
downstream of the Great Salt Lake Monday morning. Otherwise, given
the trough overhead, will maintain some limited deeper synoptic
scale forcing and isolated to scattered shower activity accordingly.
Potential for weak instability driven showers will once again yield
a relative diurnal maximum in coverage Monday afternoon, with higher
elevations also seeing a bit of an uptick, especially those
orographically favored in the increasingly northwesterly flow. Snow
levels will also remain low enough Monday to see some flakes mix in
at lower elevations at times, especially in any periods of heavier
precipitation rates. Afternoon highs remain well below
climatological normal.

Active pattern continues on Tuesday as one last trailing shortwave
digs through the backside of the lingering trough. In addition to
helping keep the colder airmass in place (snow levels and diurnal
pattern not too dissimilar from that of the prior couple days),
energy from the shortwave will help reinvigorate a bit more
widespread coverage of precipitation. Once again anticipate snow
will largely be constrained to higher elevations, but could see some
flakes mix down lower into valleys, especially near time of diurnal
min snow levels (morning) or at times of increased precipitation
rates.

More widespread precipitation finally begins to decrease late
Tuesday into Wednesday as guidance shows at least decent agreement
in a shortwave ridge trying to build in behind the trough. Less
agreement is noted in the strength of this ridge with increasing
spread in H7 temps seen amongst ensemble members, but given
agreement in at least some sort of warming, will see afternoon temps
rebound a bit closer to seasonal normal. Despite the signal for this
brief and somewhat minimal reprieve into Wednesday, guidance shows
favorable agreement in a return to a more active pattern by Thursday
onward with another larger scale Pacific trough approaching. To
further this, currently both the CPC 6 to 10 day outlook and 8 to 14
day outlook lean in favor of below normal temperatures and above
normal precipitation chances. That said, this far out uncertainty
remains a bit high on how exactly the pattern will evolve and more
specific details.

&&

.AVIATION...KSLC...The SLC terminal will see VFR conditions through
the evening with decreasing clouds. Northwest winds are expected to
shift to the southeast between 03Z and 05Z.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail
over the airspace through the evening. Scattered showers will
continue into the early evening, primarily for areas south of I-70,
through the evening before dissipating after sunset. Conditions
should stay VFR in these areas, but any of these storms will be
capable of producing gusty and erratic outflow winds.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...High Wind Watch from Saturday morning through Saturday evening
     for UTZ115-116-122.

WY...None.
&&

$$

Wessler/Warthen/Traphagan

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


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