Heavy Snow in Utah, March 22 to 27, 2024

Area Forecast Discussion
National Weather Service Salt Lake City UT
342 PM MDT Fri Mar 22 2024

.SYNOPSIS...An active weather pattern will develop across the
region Saturday and continue through at least the next week. The
first system with mountain snow and gusty valley winds is expected
Saturday into Sunday. Another strong storm with heavy mountain
snow is increasing in probability Wednesday into Thursday.

&&

.SHORT TERM (Through 12Z/6AM Sunday)...A mid level ridge axis
extends across the forecast area this afternoon, downstream from
a longwave trough situated just off the Pacific Coast. Just
upstream from this ridge axis, mid and high level moisture is
spreading across the region. This coupled with a subtle shortwave
crossing Nevada and daytime heating is resulting in isolated
scattered high based weak convection. This activity will continue
into the evening, mainly focused across northern Utah/southwest
Wyoming, with little if any precip reaching the surface given
large surface dew point depressions.

Southwesterly flow will overspread the region and strengthen
tonight through much of the day Saturday, as the upstream trough
gradually spreads inland. Ensemble guidance strongly favors
advisory level winds across west central/southwest Utah where a
few gusts into the upper 40 to low 50 mph range are expected. Prob
of exceedance of 50 mph gusts is less than 10% across this area,
thus have gone with a Wind Advisory for these areas.

Increasing large scale ascent ahead of an approaching cold front
will result in an increase in pre-frontal showers Saturday
afternoon, along with a few thunderstorms. This frontal band will
cross the Wasatch Front early Saturday evening, then continue
south across central and eventually southern Utah Saturday night.
A band of heavier precipitation will likely accompany the trailing
baroclinic zone, resulting in moderate to at times heavy snow
across the higher terrain, and generally rain along the valley
floors. A relatively short duration of 3-6 hours will limit snow
totals across the higher terrain, which are currently forecast
near the lower end of the advisory range. Given the expected
marginal nature of this initial event have held off on any
headlines at this time. Snow levels behind this band will fall to
the benches with any lingering showers.

.LONG TERM (After 12Z/6AM Sunday)...Long term period starts off with
a cold frontal boundary departing eastward as a deep trough moves
into the region. Broad and cold cyclonic flow associated with the
trough will then be maintained through Tuesday as the axis
gradually shifts east, at which point a slightly more defined
trailing shortwave will brush through the forecast region. With
sufficient lingering moisture and modest synoptic support from the
trough, will see elevated precipitation chances and a generally
unsettled pattern continue. Temperatures through this time frame
will run about 5-15F below seasonal normal.

For mountains, anticipate more or less persistent snow showers
through this time frame, especially for those that are more
orographically favored in deeper northwesterly flow. A bit of a
diurnal uptick will likely occur given modest daytime
destabilization, and could result in periods of enhanced
precipitation rates. Accumulations look modest overall, with most
guidance supporting more general daily amounts of T-2", and
amounts closer to 2-5" in those locally favored areas or places
that see some of those periodic higher rates. The best chance for
a period of slightly more impactful snow appears to by Tuesday as
the aforementioned trailing shortwave impulse adds a bit more
support.

For lower elevations, anticipate activity in general will have a
more noticeable diurnal trend, though non-zero perception chances
will remain overnight. Mean ensemble afternoon CAPE each day
builds to ~25-125 J/kg, though exact level of destabilization will
be modulated by overall cloud cover to an extent. With heating,
guidance suggests daytime snow levels should generally rise into
the 4500-5000 ft range, supporting most valley activity to remain
as rain showers. That said, given the potential convective
element to precipitation and cold airmass overhead (H7 temps
around -6C to -9C), could see some brief rate driven p-type
changes with flakes (or graupel) mixing in. Afternoon highs should
largely preclude any accumulation potential during the day. Given
the trailing shortwave, expect Tuesday to see a bit more
widespread activity. During the overnight hours in this time
frame, 25th percentile snow levels fall to as low as 4000 ft or
so, which would support a bit more snow mixing in (with better
odds at bench locations) with any lingering precipitation. Still,
short of any heavier rates, anticipate accumulation potential to
remain minimal. Best shot of seeing accumulations currently
appears to be at bench locations, with ~25% chance of an inch or
so, primarily Tuesday morning with the extra support from the
trailing shortwave.

One more forecast element to monitor will be potential for any
lake effect snow/enhancement downstream of the Great Salt Lake.
Given the strong northwesterly fetch and temperature difference
between lake and low level air, GFS derived lake effect guidance
continues to advertise ~10-20% chance of lake effect each morning.
Given potential for increased rates and the relative diurnal
minimum of snow levels, this would be the most likely way to see
any impactful snow (primarily if it would crop up near commute
times). Given the more mesoscale nature of lake effect,
uncertainty is higher at this time, and for now just remains
something to keep an eye on.

Guidance continues to show support for a quick shortwave ridge on
Wednesday to build in as the deep trough departs. Stability from
the ridge will result in much more minimal precipitation chances,
and warming H7 temps would correspond to a warmup with afternoon
temperatures back nearer to climatological normal.

Uncertainty in the exact pattern evolution grows moving towards
the latter half of the work week on into the weekend, but
deterministic and ensemble guidance sources continue to support an
active pattern taking hold once again as troughing across the W
CONUS increases. Day to day details remain murky at this time, but
the signal is further supported by the CPC 6 to 10 day outlook
and 8 to 14 day outlook, which lean in favor of below normal
temperatures and above normal precipitation chances.

&&

.AVIATION...KSLC...Lake breeze boundary currently stalled on the
western periphery of the airport still expected to gradually shift
east by 2230z allowing NW winds to prevail through 02-03z. A 20%
chance exists that showers in the vicinity will enable winds to
remain out of the south however. Enhanced southerly winds during the
latter of tonight are expected to become increasingly gusty Saturday
morning, with an 80% chance of exceeding airport weather warning
criteria after 16z, with vicinity showers once again building during
the afternoon ahead of a cold front.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions expected this
TAF period. Gusty southerly winds, strongest across central and
western Utah, will be in place through this evening, and once again
after mid morning Saturday. Increasing clouds Saturday, with showers
becoming scattered in nature for the western 2/3rds of the area
during the afternoon.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory from 9 AM to 9 PM MDT Saturday for UTZ115-116-122.

WY...None.
&&

Seaman/Warthen/Merrill

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