160
FXUS65 KSLC 271003
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
403 AM MDT Sat Sep 27 2025

.SYNOPSIS...An upper level low will gradually move through the
region, spreading precipitation chances northward as the weekend
progresses. A deepening system across the Pacific coast will then
push a modest cold front through by Tuesday, with potential for a
more robust frontal passage late in the work week.

&&

.SHORT TERM (Through 12Z/6AM Monday)...Overnight water vapor loop
shows a very evident cutoff low churning along the AZ/CA border.
Southerly flow ahead of this feature is helping to gradually
advect moisture into southern Utah, with nighttime microphysics
RGB showing a corresponding increase to cloud cover, and KICX
radar picking up on some very light transient echoes.

Moving through the day Saturday the cutoff low will make little
discernible movement. Instead, its prolonged churn will help
continue to push moisture into the region with PWAT values rising
to around 150% to 200% of climatological normal. In turn, the
combination of enhanced synoptic lift associated with the low and
diurnal destabilization will lead to increasing coverage of
showers and thunderstorms spreading northward into Utah. For
Saturday, this activity will tend to be maximized along/south of
the I-70 corridor or so. Given the cutoff nature of the low, not
anticipating the environment to have much in the way of shear
(maybe around 10-20 kts), so primary threat will be lightning,
modestly gusty outflow winds, and periods moderate to heavy
rainfall. Given the focus across southern Utah, the latter will
likely have the potential to be the most impactful due to a higher
abundance of rain sensitive basins. CAMs do suggest moderate
storm motion at least, but available moisture will result in
efficient rainmakers capable of a localized flash flood threat in
such basins. As such, those planning recreation in such places
(slot canyons, typically dry washes, slickrock areas, recent burn
scars) may want to reconsider, or at least have alternatives in
mind. The cutoff low will very slowly start to eject northeastward
overnight. While diurnal destabilization will cease, ample
moisture along with lift associated with the low will result in
continued precipitation chances, with activity also spreading
further northward.

Through the day Sunday models support the cutoff low starting to
open more into a wave and gradually lift through Utah into the
northern stream. This in turn will result in more widespread
precipitation chances spreading throughout the remainder of the
forecast region throughout the day. Mean SBCAPE values around 200-
500 J/kg and shear generally around 10 kts at best will limit the
strength of daytime convection, but PWAT values remaining around
150% to 200% of normal will support efficient rainfall production
again in whatever updrafts do get going a bit more. Like Saturday,
primary threat seems to be potential for locally excessive
rainfall, especially over rain sensitive basins. As such,
maintained "Possible" ratings in the local Flash Flood Potential
Index for recreation areas.

.LONG TERM (After 12Z/6AM Monday)...A deep longwave trough off the
U.S. West Coast will lose most of its momentum as the upstream
jet core retreats northward, favoring another cold pool/ low
pressure system off the coast of British Columbia. However,
ejecting shortwave troughs on the eastern periphery of the trough
will keep active weather in the forecast across the northern half
of the forecast area, with a cold front progged to track through
the region between Monday and early Wednesday.

Key Messages:

- A cooling trend is expected from Monday evening through
  Tuesday with highs cooling by 5-7 degrees from about Nephi
  northward.

- Scattered showers and thunderstorms are probable (40-60%
  chance)across the northern area as this wave/ front passes
  through the region, favored Tuesday morning through late Tuesday
  afternoon.

- Breezy south to southwest winds will occur south and east of
  the front, brining wind gusts up to 25-35 mph in southwest Utah
  and southwest Wyoming (pre-frontal).

While uncertainty exists with the timing of the aforementioned
shortwave trough lifting through the area, model average consensus
points toward late Monday night/ early Tuesday morning for
northwest Utah, then into Tuesday afternoon/ evening for the
Wasatch Front and areas east. There is additional uncertainty in
the overall potency of the associated frontal boundary with only
about 20% of models favoring a more aggressive front and
associated cooling trend. Majority of models ~60% support more a
glancing blow and modest cooling trend, with the remaining 20%
favoring something in between. Precipitation-wise, there is
upwards of a 60-75% chance that we`ll see light rain (0.01-0.1
inches) across the far northern Utah mountains (northern Wasatch/
Bear River Mountains) during this timeframe, with around a 25%
chance of seeing 0.5 inches or more in the mountains and valleys.

By Wednesday models continue to diverge with the overall
evolution of the offshore longwave trough, specifically with how
quickly the feature tracks eastward and brings inland impacts.
Group 1 (~45-50% of models ) depicts an open wave which would
drape a cold front across the northern area Friday/ Saturday,
group 2 (30% of models) depicts a weak wave passing north with a
ridge building into the region, and group 3 (25% of models)
depicts a deeper low moving into the region. Entertaining the
possibility of group 3... model output shows potential for one of
the coldest airmasses of the fall thus far which would support at
least some snow accumulations in the northern Utah mountains and
below freezing temperatures in the higher elevation valleys across
the region. A taste of winter. Something to keep an eye on going
forward, especially for those with crops sensitive to cold
temperatures and anyone planning outdoor activities in the high
terrain.


&&

.AVIATION...KSLC...VFR conditions prevail through the TAF period
under increasingly cloudy skies. Light southerly winds may become
interrupted by brief, but light, northerly winds through the
early morning, then switch to a more persistent northerly flow
around 17- 18Z.

.Rest of Utah and Southwest Wyoming...For northern Utah and
southwest Wyoming, VFR conditions under increasingly cloudy skies
are expected alongside light, diurnally driven winds. For
central, and southern Utah especially, another round of showers
and thunderstorms is expected throughout the day. Early morning
isolated showers will fill in from south central Utah
northeastward through KCDC and areas east. These showers will
continue northward through the afternoon into central Utah with
additional showers filling into southwest Utah. Under heavier
showers, reduction to MVFR to IFR should be expected due to VIS
restrictions alongside gusty and erratic outflow winds.

&&

.FIRE WEATHER...A cutoff low pressure system currently centered along
the CA/NV border will gradually shift northeastward through the
weekend. This will result in moisture spreading northward, with
showers and thunderstorms Saturday more centered along/south of
the I-70 corridor spreading more throughout the remainder of the
state Sunday. This system will start to lift out of the region on
Monday, but a broad area of deepening low pressure across the
Pacific coast will quickly start to bring moisture back into the
area, maintaining unsettled conditions. This system will push a
frontal boundary through the area Monday night into the day
Tuesday, with the front accompanied by precipitation and bringing
cooler conditions in its wake. While less confidence is noted late
in the period, models continue to suggest potential for a
stronger cold frontal passage and more marked cooldown late in the
work week and into the weekend.


&&

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

$$

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

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity