686
FXUS65 KSLC 301003
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
403 AM MDT Tue Sep 30 2025

.SYNOPSIS...A system advancing through the area will result in
unsettled weather through Tuesday. After a period of generally
quieter conditions through the rest of midweek, a deeper system
and associated cold front will impact the region Friday into the
weekend.

&&

.SHORT TERM (Through 12Z/6AM Thursday)...Morning water vapor loop
shows a deepening longwave trough extending from the Pacific into
the western CONUS, with an embedded wave currently advancing
through the Great Basin. Moisture has continued to increase as
this feature pushes in, with analyzed PWAT values around 0.7" to
0.8" (around 150% to 200% of normal). Analysis also shows a weak
baroclinic zone moving through accompanied by some low level
frontogenesis and subsequent cold air advection. This may further
be bolstered by some cold pool propagation from ongoing convection
nearer the UT/NV border. All that to say, a more active morning
to start off this Tuesday.

Synoptic support for ascent will continue to remain elevated
pushing into the daytime hours Tuesday. CAM guidance suggests
ongoing precipitation will become more widespread and continue to
push eastward into the area in the hours following sunrise,
especially from central to northern Utah. That said, some of the
evening runs of the high res NAM, ARW, and FV3 support increased
chances even further down across southwest Utah. Despite moderate
mid/upper level support, initial activity through the morning is
more likely to lack much in the way of good instability, so would
generally anticipate precipitation more showery in nature with a
few isolated thunderstorms mixed in. Things get a little trickier
moving into the afternoon, mainly due to some questions on how the
morning activity evolves. At a minimum, mid level lapse rates
should start to steepen, allowing some elevated instability to
develop and support a few more thunderstorms. Elsewhere where
showers and clouds are less widespread may see a bit more
destabilization overall, which in combination with jet support and
effective shear ~20-30 kts may support a few more
organized/robust updrafts. General CAM consensus would suggest any
such corridor currently is favored roughly in an area from around
central Millard County eastward to Emery and northward to around
Carbon/Duchesne. Still a good deal of uncertainty, but in any
stronger storms, would expect better potential for gusty winds and
small hail, in addition to moderately heavy rainfall.

Quieter conditions broadly will start to settle in moving into
the evening hours as the initial wave departs and destabilization
wanes. That said, another subtle embedded wave within the longwave
trough looks to rotate through and graze the UT/ID border region
as the night progresses. Not expecting too much of note, but this
looks to trigger a resurgence of some nocturnal shower chances
across northern Utah and southwest Wyoming overnight, with best
precip chances generally along/north of the I-80 corridor or so.
This wave will depart fairly quickly, and with lack of
instability, most CAMs suggest precipitation chances more or less
begin to wrap up by around sunrise.

Through Wednesday the broad Pacific longwave trough will continue
to deepen, but models show little semblance of any embedded
synoptic trigger mechanism that would move over the forecast
region. Moisture will also become a bit more limited in the deep
southwesterly flow, and thus think precipitation will largely
limited to a widely isolated shower or two along some of the high
terrain. Otherwise, this flow will promote temperatures rebounding
back upward, with forecast high marks near to a bit above normal
for the start of October.

.LONG TERM (After 12Z/6AM Thursday)...The long term period features
a trough across the western CONUS that will bring a much cooler
airmass to the region along with the potential for precipitation.
Uncertainty remains high regarding specifics related to
precipitation given that ~38% of the guidance turns this open wave
passage into a closed low which are notorious for having a lower
track predictability. The other 62% of members show a more open
wave moving through that would allow for some better
predictability.

Thursday will be the warmest and driest day of the long term as
southerly flow will be in place aiding in temperatures warming
several degrees above normal for this time of year. Moisture will
also begin to advect into the area ahead of the approaching
trough. The majority of guidance keeps this trough as an open or
semi-open wave, however guidance has been trending towards the
cutoff low scenario over the last several runs. Typically, this
type of trend favors the cutoff low scenario even though it`s not
represented by the majority of solutions (yet). Time will tell.
Currently, the wetter scenario is the cutoff low solution. The
more widespread precipitation will come along the frontal boundary
which should arrive some time between late Friday through
Saturday, pending the synoptic evolution of the approaching storm.

A reinforcing wave on Sunday will keep precipitation chances
elevated, particularly across northern Utah and SW Wyoming. H7
median temperature amongst the ensemble members is 0C by Sunday
which would be cold enough to support snow across the higher
terrain >8500 feet. The coolest air of the season is in store for
this weekend into early next week with highs ~5 degrees below
normal in the 60s across more areas. Far southern Utah will be a
bit further removed from the colder airmass with temperatures
remaining around normal.

&&

.AVIATION...KSLC...VFR conditions will persist for the KSLC terminal
through the period. An approaching cold front will increase
showery activity ahead of it along with CIGs decreasing, but
remaining VFR. Frontal timing is around noon with a transition to
light northerly flow with variable winds associated with the
showery activity. Afternoon instability could result in some
convection with lightning and gusty winds. Precipitation trends
down quickly by early evening.

.Rest of Utah and Southwest Wyoming...VFR conditions will persist
for most terminals across the airspace. A cold front moving
across the north will bring showers and isolated thunderstorms
along and ahead of the front. CIGs will likely remain above VFR
with brief MVFR conditions possible during heavier showers.
Southerly winds will be gusty ahead of the front with light
northerly flow behind the front along with variable and gusty
winds associated with convection. Winds will remain gusty out of
the south across the southern airspace with isolated (25% chance)
thunderstorm chances during the afternoon.

&&

.FIRE WEATHER...A system and a somewhat diffuse frontal boundary will
continue to track through Utah during the day Tuesday.
Precipitation chances will increase after sunrise, becoming
maximized late morning on through the afternoon hours. A few
thunderstorms will be possible especially during the afternoon,
carrying the threat of lightning, periods of moderate to heavy
rain, small hail, and gusty erratic outflow winds. This activity
will primarily be focused across central and northern Utah, with
showers and thunderstorms more isolated in nature at areas further
south in Utah. Activity will begin to wane through the evening
hours, but a quick moving reinforcing impulse will trigger some
additional showers through the overnight hours at areas closer to
the ID/UT border.

Moving into the middle part of the week (Wed/Thu), more stable
and dry conditions return. Temperatures also warm given increasing
deep southwesterly flow ahead of the next system which will be
deepening along the Pacific coast. Precipitation chances will be
minimal, but the afternoon hours will feature some modest gusts
around 20-30 mph, especially at more exposed locations.

The aforementioned deepening Pacific system will start to push
inland Friday. Winds will increase ahead of an associated cold
frontal boundary, with precipitation chances increasing along the
boundary itself. The front looks to push into the area Friday
night or so, with elevated precipitation chances lingering into
the weekend as the core of the system settles in. Potential for a
fairly substantial cooldown remains noted as well, with current
forecast carrying above normal temperatures ahead of the front
shifting to around 5-10 degrees below normal behind it.

&&

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

$$

SHORT TERM...Warthen
LONG TERM...Mahan
AVIATION...Mahan
FIRE WEATHER...Warthen

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http://weather.gov/saltlakecity