732
FXUS65 KSLC 092234
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
434 PM MDT Thu Oct 9 2025

.SYNOPSIS...Showers and thunderstorms will increase in coverage
overnight as tropical moisture continues to stream into Utah,
producing a significant flash flood threat, especially across
southern and eastern Utah. Heavy rainfall will remain a threat
through at least Saturday, with a heightened severe thunderstorm
threat on Saturday afternoon as a strong cold front crosses the
area.

&&

.DISCUSSION...
Key Messages:
* Tropical moisture will produce a significant flash flood threat
  today through Saturday, particularly across southern and eastern
  Utah. A Slight Risk (Level 2 out of 4) for excessive rainfall
  may result in flooding of slot canyons, normally dry washes,
  recent burn scars, and other flood-prone locations. Backcountry
  roads may become impassable.
* On Saturday, strong to severe storms are possible in the
  afternoon as a potent cold front sweeps through the state, with
  a Marginal Risk (Level 1 out of 5) for severe thunderstorms.
* Gusty southwesterly winds will develop ahead of this cold front
  on Saturday; the most likely gusts are to 30-40kts across
  western valleys, with a low (25%) chance of reaching 45kts.
* Snow levels will plummet behind the cold front down to as low as
  6000ft across northern Utah (7500ft across southern Utah),
  resulting in minor snow accumulations in the northern mountains.

Very active weather is in store over the next few days as
anomalous tropical moisture moving in well north of Tropical
Storm Priscilla eventually interacts with an approaching longwave
trough and associated strong cold front. This afternoon, this
tropical moisture is already surging in from the south, with PWATs
around 1" in place along the UT-AZ border. Surface dewpoints have
increased quickly along the leading edge of this surge, from the
teens and 20s early this morning, to the upper-40s to 50s. PWATs
will continue to increase statewide, reaching 250-350% of normal
by Friday morning. In addition to abundant moisture, synoptic
forcing via upper-level diffluence will provide large-scale lift
leading to this widespread rainfall. Looking at sounding profiles,
a well-saturated column will result in warm rain processes and
thus very efficient rainfall...especially across southern and
eastern Utah where that moisture is more impressive. In short,
expect a significant flash flood threat with widespread rain
falling across the state.

High-res model guidance has favored the development of a more
stubborn band of precipitation over roughly the Wasatch Front/Back
early Friday morning, which could produce several hours of
moderate rainfall. However, some members have actually moved away
from this solution, so uncertainty still remains relatively high
in this area regarding rainfall totals. Forecast confidence is
much higher across southern Utah with more persistent moderate to
heavy rainfall developing overnight and into Friday morning.
Across the south, expect a few rounds of precipitation of a more
convective mode through the day, with locally heavier rainfall
within the more widespread stratiform rain shield.

Some of the highest rainfall totals are expected over far
southwestern Utah near the Pine Valleys and Zion NP, over Boulder
Mountain, and even up near Price, where HREF/NBM guidance are
suggesting storm total precipitation in excess of 2 inches at the
50th percentile (closer to 3-3.50" at the 90th percentile).
Widespread rainfall of 1-2 inches can be expected
elsewhere...though any training of heavier rainfall rates could
locally enhance these totals.

Friday and Saturday look to be largely similar setups, with a
significant flash flood threat continuing within anomalous
moisture. However, with an approaching trough, a few changes can
be expected on Saturday. Increasing southwesterly winds may
approach advisory criteria across western valleys ahead of a
surface cold front. This approaching cold front, likely crossing
Utah between Saturday afternoon and late Saturday night, will
bring a severe thunderstorm threat along the front, as well as
plummeting snow levels and temperatures behind the front.
Regarding the severe threat, plentiful shear/dynamics coupled
with the moisture in place and limited instability will result in
mostly a wind threat, though cannot rule out the development of
some more organized storms...especially looking at some initial
model soundings Saturday afternoon that favor heightened
shear/helicity. SPC has upgraded this severe threat to a Marginal
Risk on Saturday (Level 1 out of 5).

Behind this potent cold front, snow levels will plummet down to
6000ft across northern Utah and 7500ft across southern Utah,
resulting in minor mountain snow accumulations. More intense
precipitation rates along this front could result in a quicker
drop in snow level and thus higher than forecast accumulations in
the mountains, so will need to monitor as high-res guidance comes
in. Additionally, areas downwind of the Great Salt Lake could see
some lake-effect rainfall, thus prolonging rain Sunday morning
while other areas dry out more quickly. H7 temperatures will drop
to an ensemble mean of -4C to -6C, with highs on Sunday in the 50s
along the Wasatch Front and low-70s in St. George.

Moving forward, while conditions are much cooler and dry for later
Sunday and into Monday, wetter and more active weather could
return as early as Tuesday in the extended forecast.

&&

.AVIATION...KSLC...Overall dry conditions prevail this afternoon,
with increasing mid-high level clouds into this evening. Prevailing
winds remain generally southerly through the TAF period, with
afternoon breezes tapering off around 03z. Chances for showers
arrive as early as 03z Friday, before more widespread rain fills in
after 09z. Increased instability between roughly 09-15z Friday
yields a 30% chance for thunderstorm development during this period.
Additional rounds of showers and thunderstorms are expected through
early Friday afternoon before a brief lull.

.REST OF UTAH AND SOUTHWEST WYOMING...A band of heavy rainfall and
isolated thunderstorms moving through southern Utah this afternoon
will continue to move northeastward through this afternoon. Another
round of showers and thunderstorms overspreads a majority of the
airspace overnight, leading to periodic impacts to regional
terminals through the day on Friday. Main threats will be heavy rain
that leads to reductions in VIS/CIGS to MVFR or even IFR at times,
in addition to frequent lightning.

&&

.FIRE WEATHER...Tropical moisture will bring widespread showers and
thunderstorms through at least Saturday, with the highest rainfall
totals expected across southern and eastern Utah. Chances for
wetting rains will be very high across nearly the entire state. A
strong cold front will sweep across the state between Saturday
afternoon and Saturday night, with a period of moderate to heavy
precipitation likely along the frontal passage, particularly
across northern Utah. Snow levels will drop to as low as 6000ft in
northern Utah and 7500ft in southern Utah. Conditions will dry
out behind the front on Sunday, with much cooler temperatures.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flood Watch through Saturday evening for UTZ113-117-120>131.

WY...None.
&&

$$

Cunningham/Whitlam

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