Marriott, Utah Weather Forecast Discussion

456
FXUS65 KSLC 211013
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
413 AM MDT Sun Sep 21 2025
.SYNOPSIS...An unsettled pattern persists into Monday along
with a cooldown at many locations following the passage of a cold
front. Drier conditions are then expected through midweek, with some
moisture starting to return to southern Utah late in the work week.
&&
.SHORT TERM (THROUGH 12Z TUESDAY)...A subtle weather disturbance is
crossing far northern utah this morning, flattening what is
otherwise a ridge overhead. Upstream, a couple of storm systems are
noted; a trough over the southern BritCol coast and a cutoff low off
the SoCal coast. The airmass has trended a bit drier, with PWATs
this morning ranging from 0.6-0.8 inches, lowest across the south.
However, lingering low level moisture remains in place, especially
across the north, with valley dewpoints in the mid 40s to low 50s.
A few showers continued overnight across northern Utah owing to the
aforementioned weak disturbance. However, little is left of these
showers now. Owing to the lingering low-level moisture, expect that
with increasing daytime heating, afternoon convection will develop
again across northern Utah as the airmass destabilizes. HREF
ensemble mean SBCAPE values of up to 1 kJ/kg are forecast. As such,
expect some of the storms to have decent updrafts. Convection should
be generally tied to the terrain initially. However, by early this
evening, as a cold front from the trough from the northwest
approaches the area, convection will become more loosely organized
into linear form as it crosses Utah through the night. Cooler
temperatures will then spread into the area behind it, with the
airmass then trending drier from west to east.
The trough will pinch off into a closed low over western Wyoming
tomorrow before diving into Colorado while simultaneously carving
west into Utah. This low will help maintain a few showers and
thunderstorms across eastern Utah into Monday despite a continued
drying trend. Otherwise, afternoon max temperatures tomorrow will
trend 2-8 degrees cooler than today`s highs, bringing below-normal
values back to the area from near normal today.
.LONG TERM (After 12Z/6AM Tuesday)...Despite a cooler start to the
day on Tuesday morning courtesy of an exiting trough, high pressure
quickly builds in across the region, allowing high temperatures to
return closer to seasonal averages by the afternoon. A much drier
airmass will remain in place on Tuesday areawide, keeping weather
conditions overall benign across Utah and southwest Wyoming.
Conditions from Wednesday onward will be dictated by the evolution
of a persistent area of low pressure currently located off the west
coast. Ensembles are starting to come into closer agreement on the
future track of this low, with models in support of the low
remaining off off the coast of southern California through Wednesday
before moving inland on Thursday, bringing with it an influx of
tropical moisture through the latter half of the week. This solution
favors continued dry conditions areawide on Wednesday, with
increasing PoPs on Thursday afternoon. This low is expected to
linger across the west through at least Saturday, allowing chances
for afternoon showers and thunderstorms to continue into the
weekend. The biggest question that still remains is just how far
north associated moisture spreads, as a more southerly track of the
low would keep precipitation chances mainly confined to southern
Utah.
&&
.AVIATION...KSLC...VFR conditions to persist at the terminal.
Generally light southerly winds continue this morning, transitioning
northwest around roughly 20z. Afternoon convection developing off
the Oquirrhs may impact the terminal around 20-22z, resulting in
periods of gusty and erratic winds. A more developed cluster of
convection moves in between 3-6z, which will be capable of producing
brief heavy rain, lightning, and erratic winds.
.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions persist for all
regional terminals through the period. Winds remain generally light
and terrain driven, outside of periods of potentially gusty and
erratic winds at northern Utah and southwest Wyoming terminals this
afternoon and evening as widely scattered showers and thunderstorms
develop.
&&
.FIRE WEATHER...A few morning showers will continue over northern
Utah as a weak disturbance crosses northern Utah. With lingering low-
level moisture in place combined with daytime heating, expect a
transition to mainly terrain-based thunderstorms this afternoon,
some of which will be wet. By early evening, the next storm system
will approach Utah from the northwest. Showers and thunderstorms
will then become more loosely organized into more of a band near the
cold front as it crosses northern Utah tonight.
Cooler and drier conditions will settle into the area behind this
cold front on Monday. That said, lingering showers and thunderstorms
can still be expected especially across eastern Utah tomorrow as the
storm system continues to carve into the area. The drying trend will
continue through at least midweek. Thereafter, a meandering low
pressure system will eventually approach Utah, potentially by
Friday, bringing another period of unsettled weather to at least
southern Utah.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
Cheng/Whitlam
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NWS SLC Office Area Forecast Discussion