Alpine, Utah Weather Forecast Discussion

034
FXUS65 KSLC 212120
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
320 PM 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.
&&
.DISCUSSION...
Key Messages:
* Scattered showers and thunderstorms continue across northern
  Utah through Monday, with the best chance of wetting rain across
  northern Utah late Sunday night through early Monday morning.
* Minimally impactful elevated canyon winds are expected early
  Tuesday morning for Washington County canyons with even more
  limited canyon winds possible for Davis and Weber County canyon
  exits Tuesday morning as well as Tuesday night into Wednesday
  morning.
* Temperatures trend below normal Monday through Tuesday with
  temperatures then moderating back to, and just above, normal
  Wednesday into Thursday with generally dry weather in place.
This afternoon a weak convergence boundary over northern Utah,
roughly along and south of the I-80 corridor is helping to
invigorate isolated to widely scattered showers and thunderstorms.
With limited instability in place along this axis, showers and
thunderstorms along this axis are generally expected to remain on
the weaker side with some isolated briefly moderate to heavy
rainfall. Meanwhile, back to the west, a trough moving in through
Washington and Oregon is helping to H5 heights across northeast
Nevada and southern Idaho, which is coincident with a better pool
of instability and a bit more vigorous convection. High res
ensembles are in excellent agreement that this well forced area of
convection will move across northern Utah tonight, with a general
consensus of showers and thunderstorms moving through the Wasatch
Front between 10pm and 1am, and eventually across SW Wyoming and
the Uinta Basin through 3-5am, while weakening. While ensemble
means are generally around 0.05 to 0.15 inches for precipitation
overnight, the upper range of potential is as high as 0.5 to 1
inch of precipitation where any heavier showers and thunderstorms
are able to reside, with the best corridor for this locally
heavier rain somewhere between Salt Lake and Utah Counties. A
trailing line of showers and thunderstorms will then move across
northeastern Utah Monday morning through early afternoon as the
trailing upper level vort max moves through southwest Wyoming,
with the associated convection moving off into eastern Utah by
Monday afternoon.
Behind the cold front on Monday morning, temperatures will trend
below normal with highs only in the low to mid 70s across northern
Utah valleys for Monday and Tuesday. Drying conditions will bring
generally pleasant weather by Tuesday. Initially the northerly
winds late Monday night into Tuesday morning with increasing
pressure gradient across southern Utah will help develop some
limited canyon winds across Washington County including out of
Blackridge Canyon. Current guidance suggests sub-advisory winds
generally in the 30 to 40 mph wind gust range. Similarly across
northern Utah a weak easterly pressure gradient will develop
across the Wasatch, but with very light 700 winds and minimal
temperature advection, expect only limited canyon winds to develop
Tuesday morning and again Wednesday. Again winds look sub-advisory
there as well, with gusts in the 25 to 40 mph range but only for
areas very close to prone canyon exits, primarily in Davis and
Weber Counties.
For the remainder of the extended forecast, a general warming
trend will bring temperatures back to and just above normal by the
second half of the week. Generally dry conditions will remain in
place through mid-week. However by the end of the week, there is
potential for moisture sneaking back into southwest Utah. There
remain more uncertainty that usual with this increase in moisture
as it is dependent on the track of a slowly meandering upstream
cutoff low moving onshore. Overall the ensemble mean has trended
toward evolving this trough southward into Arizona as we move into
next weekend. Thus southern Utah will likely remain on the
periphery of the deeper moisture, but this will still increase the
chances for daily isolated to scattered showers and
thunderstorms.
&&
.AVIATION...KSLC...VFR conditions will persist for the KSLC terminal
through the period. Mostly dry conditions will likely continue for
the remainder of the afternoon with rain and embedded thunder
returning between ~04-07Z ahead of a cold front. Cold front passage
will occur ~15Z tomorrow with some spotty showers along and behind
the front in addition to a northerly wind switch.
.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist
for the airspace through the period. Conditions across the southern
airspace will remain dry. Isolated and short lived afternoon
convection will gradually diminish across the north with a return of
some rain with embedded thunder late tonight in advance of a cold
front. Frontal passage timing across the north will occur between 12-
17Z with winds shifting out of the north. Spotty showers along and
behind the front are expected.
&&
.FIRE WEATHER...
This afternoon isolated to scattered showers and thunderstorms
will impact areas roughly along and just south of the I-80
corridor in northern Utah. Drier air in place across southern Utah
with high pressure building over southern Utah will keep dry
conditions in place. Tonight an approaching low pressure system
will bring a more organized area of showers and thunderstorms from
west to east across Northern Utah overnight. This is when the
greatest chance of wetting rain will occur over northern Utah.
Ensemble means range from around 0.05 to 0.15 inches of rain over
northern Utah, but where thunderstorms are able to be more focused
a half inch to three quarters of an inch of rain cannot be ruled
out.
On Monday, a cold front will move across northern Utah which may
bring a reinforcing round of scattered showers and thunderstorms
particularly across northeastern Utah along with trending
temperatures below normal for Monday and Tuesday, with valley high
temperatures only in the low 70s across northern Utah. Southern
Utah will remain dry through this timeframe.
Temperatures will moderate Wednesday through the end of the week,
trending back to near normal to slightly above normal by
Thursday, with generally dry conditions in place Tuesday and
Wednesday. By Thursday into the weekend, limited moisture will
start to work its way back into Utah from the southwest. This will
eventually start to increase the chances for isolated to widely
scattered showers and thunderstorms by late in the week.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
PUBLIC...Church
AVIATION...Mahan
FIRE WEATHER...Church
For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

NWS SLC Office Area Forecast Discussion