859
FXUS65 KSLC 211009
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
409 AM MDT Tue May 21 2024

.SYNOPSIS...A cooler and more stable airmass will reside across
much of the area today as a trough begins lifting out of the
region. Increasing southwesterly flow will bring a brief warming
and drying trend Wendesday, before the next cold front pushes
through the region late Wednesday through Thursday. The pattern
will remain active through the upcoming weekend.

&&

.SHORT TERM (Through 12Z/6AM Thursday)...A broad upper trough
continues to slowly swing through the region early this morning.
The associated surface front has pushed south and east of the
forecast area, while the trailing 700mb baroclinic zone currently
stretches across southern Utah. A weak shortwave trough embedded
within the mean cyclonic flow is currently riding along this
boundary, and resulting in an area of showers spreading into
southwest Utah at the present time. This area will quickly spread
east, likely exiting the forecast area near or shortly after
sunrise.

In the wake of the frontal boundary, a much cooler airmass resides
across the forecast area this morning, and will keep max
temperatures confined to the low-mid 60s across northern/western
valleys including the Wasatch Front (roughly 10F below climo),
and near 80 around St George.

In the wake of this wave, southwesterly flow will quickly develop
across the forecast area by early Wednesday, and then strengthen
throughout the day. This will result in a brief warming and drying
trend area-wide, as max temps trend roughly 8-12F warmer. This
warmup is in advance of the next cold front, which will reach
northwest Utah late Wednesday afternoon, then sweep across much
of northern and central Utah Wednesday night. The associated
shortwave trough digging into the Snake River Plain/northern Great
Basin will interact with the frontal boundary to bring a chance
for precipitation across northern Utah Wednesday evening into
Wednesday night.


.LONG TERM (After 12Z/6AM Thursday)...Long term forecast period
begins with a shortwave trough moving east into the Northern
Rockies, with an associated cold frontal boundary moving southward
through Utah. This front continues to appear fairly dry in nature,
with most guidance (including what limited high res CAM guidance is
now available) suggesting just some light showers along/near the
front, and largely remaining north of US-40 or so. Boundary still
looks to stall somewhere near to a bit south of the I-70 corridor as
the parent shortwave continues eastward, with much cooler
postfrontal temperatures settling. To that point, Thursday afternoon
highs for locations behind the front look to be around 5 to 15
degrees cooler than that of Wednesday. Aside from temps/precip,
still seeing potential for some prefrontal wind gusts ~25-40 mph,
generally across southern and eastern Utah, as well as some gusty
postfrontal winds in portions of the southwest Wyoming. For Friday,
remnant boundary will likely remain draped somewhere across central
Utah, and help trigger some isolated to scattered diurnal showers as
weaker trailing energy advects through overhead. Airmass will
moderate during the day as well, so will see temperatures begin to
rebound back upwards.

Warming temperatures continue into Saturday as the old baroclinic
zone washes out and H7 temperatures increase. As a result, expect
daytime highs Saturday near to maybe a bit below climatological
normal for late May. Continued energy advecting through in advance
of another approaching shortwave will once again trigger some
isolated to scattered showers across the forecast region. General
consensus amongst guidance is that this shortwave and associated
cold front take a similar progression to the prior system Saturday
evening into Sunday, with the fairly dry front moving south and
stalling/washing out across central Utah Sunday. The exception to
this scenario appears to be something akin to the deterministic
Canadian model (and supported by ~30% of ensembles) where shortwave
is more disjointed/weaker, and thus any surface reflection is much
more muted. That would likely be a drier and more mild scenario, but
for now kept NBM guidance for Sunday which includes a cooldown of
several degrees from central Utah northward in addition to some
continued isolated to scattered showers.

A bit of uncertainty remains for Memorial Day, with around 55% of
ensemble membership supporting a quick building ridge, and the other
45% maintaining some sort of weak lingering trough influences. For
the ridge scenario, dry conditions and normal to slightly above
normal temperatures would be expected. For the weak/lingering
trough, a more muted warmup and maybe some isolated precipitation
chances (generally further north in the forecast region) would be a
bit more likely. In any case, little suggests anything of a washout
type of day or much in the way of anything substantial at this time,
but those with outdoor plans may want to keep an eye on the forecast
all the same. Almost all guidance then supports further building of
a ridge moving into midweek, with dry conditions and warm
temperatures favored. While out just beyond the general time period
of this forecast (and subject to change being over a week out),
current NBM guidance even carries a 25% chance for KSLC to see its
first 90 degree day on Wednesday 5/29. For context, the mean first
90+ degree day for KSLC specifically is 6/3, so not too far off all
things considered.

&&

.AVIATION...KSLC...Very isolated lake enhanced showers possible
through mid morning or so. Winds fairly light and variable, likely
becoming NW between ~15-17Z. Isolated afternoon showers anticipated
to remain east of the terminal, though if showers manage to
develop/collapse over the terrain just to the east, could see some
brief periods of easterly winds try to push in. NW winds largely
favored to persist though, with a shift back to SE ~03-04Z Wed.


.REST OF UTAH AND SOUTHWEST WYOMING...System will continue to
depart the area through the TAF period. Some isolated afternoon
showers possible at northern terminals, primarily at terminals
east of Utah`s high terrain (e.g. LGU/HCR/EVW). VFR conditions
largely expected to persist, though brief MVFR possible with any
heavier showers. These showers could also produce brief
gusty/erratic outflow winds. Otherwise, expect most terminals
(excluding ENV) to carry a more northerly wind component during
the day, with some modest gusts possible (primarily at southern
terminals).

&&

.FIRE WEATHER...A cooler and more stable airmass has settled
across the region in the wake of Monday`s cold front, keeping
daytime temperatures roughly 10 degrees below normal. Lingering
moisture across northern Utah will maintain a chance for showers
mainly east of I-15 while the remainder of the area remains
generally dry. Despite the cooler airmass, drier air will quickly
mix down across central and southern Utah, resulting in RH values
falling near or below 15 percent this afternoon across lower
elevations, and low to mid 20 percent range over the higher
terrain of southern Utah.

Increasing southwesterly flow Wednesday will bring a warming and
drying trend across the area. Daytime temperatures will trend
8-12 degrees warmer state-wide, while RH values trend 4-8 percent
lower. A cold front will reach far northwest Utah Wednesday
afternoon, then push through the state Wednesday night through
Thursday. Temperatures will trend 8-12 degrees cooler across
northern and central Utah Thursday, while the airmass ahead of the
front remains warmer across southern Utah. Any precipitation with
this system looks to remain confined to northern Utah.

The unsettled pattern looks to continue into the upcoming
weekend, before a more pronounced warming and drying trend sets
up beginning early next week.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Seaman/Warthen

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