859
FXUS65 KSLC 250938
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
338 AM MDT Sat May 25 2024

.SYNOPSIS...A low pressure system will bring widespread rain
with embedded thunderstorms across much of the region. A
relatively cool and stable airmass will spread across the area
Sunday, followed by a substantial warming trend early next week.

&&

.SHORT TERM (Through 12Z/6AM Monday)...A multi-faceted upper
trough will cross the forecast area today, bringing fairly
widespread precipitation across northern and central Utah, along
with cooler temperatures across the region. Initially this morning
a SW-NE oriented baroclinic zone stretches from roughly Cedar City
to Vernal, and has been the focus for several rounds of showers
overnight. A shortwave feature noted in satellite imagery crossing
the southern Great Basin will ride along this boundary this
morning, maintaining shower activity in the vicinity of the
boundary through sunrise.

Attention then turns to an upstream shortwave trough currently
crossing the northern Great Basin and inducing numerous showers
across northern Nevada. This wave will amplify a bit as it
translates across the forecast area today. Showers will increase
within a region of large scale ascent across northern Utah through
this morning, with most CAM guidance suggesting at least a broken
line of convection surges through northern and central Utah late
this morning through early afternoon, followed by more scattered
band of showers later in the afternoon. Small hail, lightning,
gusty winds to 45 mph, and lightning will be common with the
stronger cells. If enough clearing develops ahead of the
convective line allowing surface heating and sufficient
instability, it`s not out of the question outflow along localized
portions of the line could exceed 50 mph and approach severe
thresholds, particularly across the western Uinta Basin and Castle
Country/San Rafael Swell. Any lingering convection should wind
down by sunset as the parent wave moves east of the area. Snow
levels through the event will generally remain near or above 9000
feet, and could see some accumulation along the higher ridgelines
of the Wasatch as well as across the western Uintas.

With abundant cloud cover and precipitation across northern and
central Utah today, temperatures will trend considerably lower and
run roughly 10F below climo, with maxes remaining confined to the
low 60s along the Wasatch Front. The cooling trend across southern
Utah will be less pronounced, as temperatures trend roughly 5F
cooler today.

Mid level ridging will begin to amplify upstream in the wake of
the departing storm system Sunday, leaving the forecast area with
a relatively stable northwest flow. The airmass will modify as
heights slowly rise, allowing max temperatures across northern
Utah to trend 6-10F warmer, remaining a few degrees below climo.
Temperatures across southern Utah will trend close to 5F
warmer, allowing max temps to approach 90F in the St George area
Sunday afternoon.

.LONG TERM (After 12Z/6AM Monday)...A sharp warmup will be
underway on Memorial Day across Utah and SW Wyoming as a
transient, albeit strengthening mid-level ridge axis will traverse
eastward across the region. When compared to today (Saturday),
expect a very noticeable nearly a 20F warmup on Monday across
northern and central Utah, with about a 10F warmup across southern
Utah. NBM probability of 90F at SLC has climbed to 38%, now
centered on Wednesday. The mean first 90F day in SLC is June 8, so
we`re not too far off the mark should 90F be reached. A well-
clustered model consensus with high forecast confidence early in
the week then begins to wane as the above- mentioned ridge axis
exits to the east by Tuesday-Wednesday, with increasing deep-layer
SW flow developing on Tuesday as an area of low pressure moves
into coastal British Columbia. As this evolution transpires,
additional warming will be in store for Tuesday, with temperatures
reaching the mid to upper 80s across the Wastach Front, and the
upper 90s across Lower Washington County. We can`t rule out an
isolated shower or thunderstorm by Tuesday afternoon, mainly over
northern Utah and SW Wyoming.

Similar to yesterday`s forecast, uncertainty begins to emerge by
midweek, with the greatest source of uncertainty regarding the
track, strength and timing of the aforementioned low. We now see a
clearer signal for the emergence of two forecast scenarios
appearing by Wednesday and carrying us through early next weekend,
and those two scenarios are a ridge vs a trough scenario, with a
slight (about 60% of the solution space) nudge towards the trough
scenario. Should the ridge remain in place, warm, mainly dry
conditions would be the most likely outcome through the remainder
of the forecast period. The trough solution would bring a mid to
late week reduction in temperatures back closer to average (or
even below average in the stronger trough solutions) with periods
of showers across northern Utah and SW Wyoming as well as gusty
winds on the periphery of the trough. Given the uncertainty and
the nearly equally divided model solution space, it`s too early to
pick a ridge or trough solution as a most likely outcome. It is
worth mentioning that models are trending very gradually towards
the trough idea, and this is supported by the most recent runs of
deterministic, global models as well. Finally, this trend is also
reflected in the official forecast which shows gradual cooling
Thursday and Friday.

&&

.AVIATION...KSLC...A disturbance and associated cold front will
sweep across the terminal this afternoon bringing a myriad of
impacts. First, gusty S winds (15-25kts) anticipated this morning
with showers in the vicinity. Line of showers with embedded
thunder expected to move across the terminal between 17Z-20Z,
complete with gusty, erratic outflow winds, lightning and perhaps
small hail. Can`t rule out brief reductions to MVFR (25% chance)
with a 10%, with a chance for brief IFR conditions. In the wake of
this wave, isolated to scattered showers and isolated
thunderstorms linger through about 03Z. Wind direction forecast is
highly uncertain after 18Z due to the shower/storm activity, but
confidence increases in the emergence of S winds around 02Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Disturbance and associated
cold front will move across Utah and SW Wyoming this afternoon. In
advance of these features, band of showers will continue across
central and NE Utah this morning, with pockets of mountain
obscuration. Clusters of showers and thunderstorms will then move
across central and northern Utah as well as SW Wyoming later this
morning through the afternoon hours. This activity will produce
gusty, erratic outflow winds, brief reductions in CIG/VIS to the IFR
category, lightning and small hail. This activity will gradually
diminish this evening, leaving tranquil conditions overnight.

&&

.FIRE WEATHER...A low pressure system will bring widespread
showers accompanied by wetting rains to much of northern, central
and southwest Utah today. Scattered thunderstorms can also be
expected. Precipitation will be more scattered in nature across
south central and east central Utah. With the passage of this
system, gusty winds can also be expected across the western Uinta
Basin and the San Rafael Swell region.

A more stable airmass behind this system will spread across the
region Sunday which will keep temperatures several degrees below
normal. A substantial warming trend will begin Memorial Day, and
continue through midweek, pushing temperatures 10 degrees above
normal by Tuesday. This airmass will remain in place Wednesday as
southwesterly flow increases, resulting in very dry and breezy
conditions Wednesday afternoon. A mostly dry cold front is
expected Thursday cooling temperatures a bit and switching winds
to the northwest.

&&

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

$$

Seaman/ADeSmet

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