High Wind Watch 1, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
401 AM MST Wed Feb 28 2024

.SYNOPSIS...A break in the active weather will bring warming
temperatures to the region through Thursday. A strong winter storm
will bring mountain snow to far northern Utah Thursday evening.
Strong winds ahead of a cold front can be expected across the
western valleys Friday afternoon and evening and again Saturday
afternoon and evening. This cold front will shift south and east
across the region Saturday evening into Sunday, bringing snow
levels to valley floors for much of the state and much colder
temperatures.

&&

.SHORT TERM (Through 00Z Saturday)...A break in the active weather
is in store for the first portion of the short term forecast
period. Morning upper air and satellite analysis indicates
shortwave ridging shifting across the Northwest. A weakening upper
level low is crossing the southern portions of the Desert
Southwest. The next significant winter storm is developing across
the Gulf of Alaska with a strong north-south jet with a nearly
straight shot from the arctic.

Expect upper level ridging to gradually shift eastward into the
High Plains through Thursday night. This will bring warming
temperatures to much of the region, with another preview of
spring.  It won't last however.

As the previously mentioned upper level trough continues to
strengthen and shift southward, upper level diffluence associated
with a 140kt+ jet maxima will shift into the West. This will
coincide with increasing moisture and favored west to southwest
flow across the Wasatch Mountains north of I-80 Thursday night
into Friday. Expect periods of snow to develop across the Wasatch
Mountains north of I-80 Thursday night and slowly shift south
Friday morning into Friday afternoon as the main trough gradually
shift south and east near the Pacific Coast.

Meanwhile, strong winds can be expected across the western
valleys. Guidance has been consistent with this pattern for days.
For example, the EPS based Extreme Index has significant
anomalies, approaching the highest values on the scale by Friday
afternoon across the western valleys. Guidance suggests widespread
700mb winds between 50-60kts. The question will be how much these
winds will surface across the western valleys.

Looking at the ensembles, a significant portion of the ensemble
members also support at least 45 mph wind gusts (>80% chance) for
the western valleys. Going further, around 30-40% of the ensemble
members would support wind gusts approaching 58 mph (high wind
watch criteria). Given the support for wind gusts greater than 58
mph is less than 50%, did not issue a High Wind Watch with this
package. Current thinking is this will end up being a high end
wind advisory event.

For more on the return to winter, with valley snow and heavy
mountain snow, see the long term forecast discussion.

.LONG TERM (After 00Z Saturday)...Forecast period begins in a
prefrontal environment as a strong trough gradually digs into the
area from the PacNW. This trough and front will move through and
result in a period of impactful weather through Sunday or Monday,
including gusty winds, substantial mountain snow accumulation, and
valley rain transitioning to snow as the cold front passes. Very
cold air will also settle in behind the front.

For winds, deep layer southwesterly flow will be in place, with a
corridor of 700mb winds in approximately the 40-60 kt range. As a
result, the signal remains favorable for correspondingly strong
wind gust potential to the surface across much of the region. The
ECMWF Extreme Forecast Index continues to highlight much of the
forecast region in shading depicting winds very anomalous relative
to climatology. NBM probabilities continue to show greater than
80% chance of max wind gusts exceeding 45 mph (Wind Advisory
Criteria) across the West Desert and most western Utah Valleys.
Increasing chances are also noted from south central into
southeastern Utah as the day progresses. With such high momentum
air lurking just above the surface, gusty winds will likely
persist overnight into early Saturday... But better chances are
expected after sunrise when thermal mixing can increase. That
said, will be dealing with increasing cloud cover as a potential
limiting factor, though precipitation will be an efficient means
to transfer this high momentum air downwards as well. In any case,
widespread sub-advisory wind gusts in the 30-45 mph appear likely
for almost the entirety of the forecast region, along with the
aforementioned upper end potential. While a period of gusty
northwesterly winds will be possible following the passage of the
cold front midday Saturday into early Sunday, overall anticipate
lessening winds as the front further progresses.

Precipitation will also be widespread with this system. Moist
southwesterly upslope flow will be ongoing early Saturday, with
increasing jet support yielding elevated precipitation chances
spreading southward as the day progresses. Precipitation will then
become better focused along a cold frontal boundary that will
move through, with guidance continuing to highlight midday
Saturday into early Sunday as the most likely time frame for this
frontal passage. Lingering moisture will yield continued post-
frontal precipitation chances (especially for higher terrain
favored in west to northwesterly flow) through Sunday, with
activity becoming more limited by Monday as moisture further
decreases and any larger scale synoptic forcing mechanisms likely
become ill defined or shift. Ensemble 75th/25th percentile 700mb
temps start around -2C/-5C on the warm side of the boundary, and
fall to around -13C/-16C on the cold side. This will result in
prefrontal snow levels above 6000 feet rapidly falling with
frontal passage. In turn, valleys will likely see a quick p-type
transition to snow, with continued signal for a period of
accumulating snow in many locations thereafter. Uncertainty
remains in the exact snow amounts (especially lacking higher
resolution guidance), though current NBM median amounts generally
come in around the 1-4 inch range. Higher confidence is noted in
substantial mountain snow, with current storm total amounts
indicating a general 1 to 2 feet, with locally up to 3 feet
possible in some of the locally favored areas before snow finally
tapers off.

Cold air will settle into the region following the passage of the
cold front, with temperatures falling to around 10F-20F below
climatological normal for early March. Uncertainty noted on the
pattern evolution moving into midweek, with around 70% of ensemble
members supporting at least a brief period of more benign weather
Tuesday... But the general consensus in guidance then supports the
active pattern of late kicking back in soon thereafter.

&&

.AVIATION...KSLC...Mostly quiet conditions expected this forecast
period. VFR conditions prevail, with clear to mostly clear skies.
Some mid level clouds between ~10-15kft likely build in late
Wednesday into early Thursday. Biggest uncertainty noted on
Wednesday afternoon wind shift. In general, continued southerly
winds slightly favored, but guidance suggests a brief period of
northwesterly winds possible ~23-03Z. In any case, wind magnitudes
should remain fairly light, largely less than 10 kts.

.REST OF UTAH AND SOUTHWEST WYOMING...Fairly benign conditions
anticipated this TAF cycle. VFR conditions expected to prevail, with
LGU as the only potential exception (~10% chance of BR/FG
development early Thursday morning). Some increasing VFR cloud cover
likely (mostly at northern terminals) Wednesday night into Thursday.
Winds at area terminals anticipated to remain light with magnitudes
largely less than 10 kts.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Watch from Thursday evening through Saturday
     evening for UTZ110.

WY...None.
&&

Kruse/Warthen

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