Heavy Snow and High Wind in Utah, March 29 to 31, 2023

Area Forecast Discussion
National Weather Service Salt Lake City UT
424 AM MDT Wed Mar 29 2023

.SYNOPSIS...Southwesterly flow will strengthen across the region
today, ahead of the next cold front which will arrive this
evening. The associated storm system will maintain cold and
unsettled conditions through the remainder of the week.

&&

.SHORT TERM (Through 12Z Saturday)...Southwesterly flow aloft
prevails across the forecast area early this morning, downstream
from a longwave trough anchored around an upper low spinning just
off the northern California coast. The surface front associated
with this trough currently extends across central NV from roughly
Elko to Tonopah, with precipitation trailing this boundary along
the low level baroclinic zone.

The upstream low is forecast to dig along the northern/central
California coast through this evening, while a shortwave trough
rounding the base of this low ejects inland and across the Great
Basin today, slowly pushing the surface boundary east to near the
UT/NV border this afternoon. Pressure falls ahead of this front
will result in windy conditions across much of southern and
western Utah this afternoon and evening. Have maintained going
Wind Advisory across the western valleys, but will need to monitor
for a potential upgrade given the strength of the flow aloft
(exceeding 50 kts at 700mb by 21Z) and the strength of the
isallobaric forcing. However, extensive cloud cover may limit
mixing and keep winds below warning criteria. Have kept the Salt
Lake Valley below advisory criteria, as well as the St George
area eastward across south central UT, where upslope component
should limit the strength of the gusts to some degree.

As the upper trough spreads inland tonight, the associated surface
front/trailing baroclinic zone will push east across the forecast
area, reaching the I-15 corridor late in the evening. This will be
accompanied by a period of heavy precipitation along/behind the
boundary, continuing into the overnight hours. Snow levels should
remain just above the valley floors through most of the event, but
may lower at times within periods of heavier precipitation.

A break in precipitation will follow this boundary late tonight
into Thursday morning, before the upper trough crosses the
forecast area Thursday afternoon/evening bringing fairly
widespread snow showers. This will be followed by a period of
unstable northwest flow favoring the I-15 corridor and adjacent
terrain of northern Utah Thursday night into Friday morning, where
mountain locations favored in northwest flow could do quite well.
The upper trough will pull east of the area Friday afternoon
bringing an end to precipitation by Friday evening.

Regarding winter headlines, have maintained the going Winter Storm
Watch for the northern and southern mountains with this package,
as snowfall totals are expected to border on the advisory/warning
line, and impact may be mitigated by late evening onset across
the higher terrain. The second round of snowfall later Thurdsay
into early Friday across the north may end up being the more
impactful period.

.LONG TERM (After 12Z Saturday)...The Great Basin will be between
storms to start the period Saturday morning. Subtle ridging will
result in dry conditions before another arctic airmass pushes into
the region, sparking more precipitation across the entire area late
Sunday through late Monday/early Tuesday. Temperatures will also go
from ~5 degrees below normal Saturday/Sunday to ~15 degrees below
normal Monday through Wednesday as the arctic airmass settles into
the region. There will be a break in precipitation on Tuesday as the
first trough shifts east, however guidance diverges a bit on when
how the aforementioned trough propagates which will determine
whether we enter a drier or wetter regime.

The period begins with an arctic airmass pushing into the PNW
Saturday morning. A 100+kt jet will be positioned over southern
Idaho/northern Utah overnight Saturday. Northern mountains closest
to this jet max will start to see snow develop by early Sunday
morning. As a trough deepens and pushes into the Great Basin on
Monday, precipitation will start to become more widespread over
valleys. A baroclinic zone will sweep across the state Monday with
southwesterly flow transitioning to northwesterly flow post-frontal.
A band of precipitation will form along this boundary with valley
rain transitioning to snow, and all snow above 6000-6500 feet.
Behind the front H700 temperatures approach -14C (50th percentile of
ensembles), with the 25th-75th percentiles ranging from -12 to -15C.
With some lingering moisture and northwest flow there is currently a
low chance (10% chance) for lake enhanced snow across the Wasatch
Front Tuesday morning. Given H700 winds will likely have more of a
northerly component, the area of emphasis will be on the Tooele and
Salt Lake valleys.

After Tuesday morning there is uncertainty around how the broad
trough across the PNW migrates. 42% of ensemble members suggest an
easterly migration of this trough that would result in a drier
solution for Utah/SW Wyoming, however 58% of members opt for keeping
the parent trough to our NW which would keep us in a position
favorable for more precipitation.

&&

.AVIATION...KSLC...VFR conditions will prevail for the KSLC terminal
for most of the period. A storm moving into the area will keep
southerly winds strong and gusting near 25kts throughout most of the
day. A line of heavy rain, snow, and graupel with embedded lightning
(20% chance) will form across western Utah by 00Z and move into the
terminal area between 04-06Z creating brief MVFR/IFR conditions due
to reduce VIS and lowering CIGs.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will transition
to MVFR/IFR conditions throughout the afternoon/evening from west to
east as a line of storms develops across western Utah and pushes
east. Precipitation will be a mixture of rain, snow, graupel, and
embedded lightning (20% chance). During the day, southerly winds
will be strong and gusting near 40kts in western and southern Utah
(closer to 25kts across northern Utah/SW Wyoming). These winds will
weakening throughout the evening as the line of storms pushes
through. CIGs will also drop to below mountain obscuration levels.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory from noon today to 9 PM MDT this evening for
     UTZ101-102-115-122.

     Winter Storm Watch from this evening through Friday evening for
     UTZ110>112.

     Winter Storm Watch from this evening through Thursday evening
     for UTZ125.

WY...None.
&&

Seaman/Mahan

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