816
FXUS65 KSLC 090905
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
305 AM MDT Thu Oct 9 2025

.SYNOPSIS...Tropical moisture surges north into Utah today kicking
off a period of heavy rain and an attendant flash flood risk. While
heavy rain is expected across the majority of Utah over the next
three days, the highest risk for flash flooding exists across
southern and eastern UT with an isolated flash flooding risk further
north. Additionally, a strong to severe thunderstorm risk exists
late Saturday evening across northern UT as a cold front sweeps
across the state. Following the frontal passage, cool and dry
conditions will prevail Sunday and Monday.

&&

.DISCUSSION...
Key Messages:
* The threat for flash flooding begins to increase today, increasing
  through Saturday with a particular emphasis on southern and
  eastern UT as moisture associated with Tropical Storm Priscilla
  surges north.
* A risk for isolated flash flooding pushes toward northern UT
  Friday and Saturday.
* On Saturday, strong to severe storms are possible in the afternoon
  as a cold front sweeps through the state.
* A brief respite from the unsettled weather pattern will persist
  Sunday and Monday in the wake of the aforementioned cold front.
* Unsettled weather looks to return by Tuesday next week as another
  trough approaches the area.

An anomalous and potentially hazardous precipitation event is
expected to unfold across UT beginning today through Saturday as
moisture from Tropical Storm Priscilla advects north into UT. This
moisture is expected to interact with an incoming upper trough
pushing into the area from the Pacific NW, resulting in a prolonged
period of heavy rain across the state with an attendant risk for
flash flooding with a particular emphasis across southern and
eastern UT.

While Priscilla remains well to our south, associated moisture is
already beginning to advect north over southern UT today,
continually creeping north through Saturday. Currently, the bulk of
the moisture remains over southern AZ per satellite water vapor
imagery, and is expected to reach southern UT this afternoon.
Interestingly enough, today and Friday feature a synoptic pattern
similar to that of a Predecessor Rainfall Event (PRE). A PRE is when
moisture from a a tropical system is picked up within the mean flow
and advected well ahead of the main storm. This moisture then
interacts with a forcing mechanism, such as a stalled frontal
boundary or a jet streak. In our case, looking in the very upper
levels, it appears that a subtropical jet forms just ahead of the
incoming trough draping itself SW/NE across southern NV to western
WY. Where this setup becomes interesting is the fact that roughly
northern AZ and southern UT sit within the right entrance region of
this feature which is where upper level divergence, more favorable
ascent, and perhaps instability is found. With the moisture from
Priscilla streaming into the region while this jet streak is in
place, a heavy and potentially dangerous rainfall event appears
possible this afternoon and evening across southern UT.

On Friday, moisture will continue to surge north increasing chances
for precipitation across the entirety of the forecast area. At the
same time, moisture continues to increase in quality and become
deeper across southern and eastern UT, perhaps yielding heavier and
more efficient rainfall with storms across the aforementioned region
as a result. The aforementioned jet streak aloft is expected to
weaken somewhat during the earlier hours of Friday, though
reinvigoration appears likely as hi-res guidance has honed in on
this solution. Southern and eastern UT, unfortunately, still remain
in the right entrance region of the jet streak where a more
favorable parameter space is found, resulting in an increased threat
for flash flooding across the aforementioned areas. One limiting
factor could be that storm motions are expected to be somewhat
quick, though as previously mentioned, moisture quality will all but
increase through Friday resulting in markedly heavy rainfall from
these storms.

A strikingly similar parameter space will exist across southern and
eastern UT on Saturday as flow aloft strengthens with the approach
of an upper trough. The main difference with Saturdays setup will be
across northern UT where kinematics begin to see an increase due to
the approach of the upper trough. At the surface, a cold front is
expected to begin sweeping through the state in the afternoon hours
associated with the ejecting upper trough. Increasingly favorable
ascent will develop during this, likely sparking a line of
thunderstorms along the cold front as it treks across northern UT.
Quite an interesting environment exists ahead of these storms with
effective shear generally ranging from 40-50kts and SRH generally
ranging from 150-300 m2/s2 overspreading the majority of northern
UT, though instability remains quite weak with MLCAPE generally
ranging from 250-500J/kg. Despite weaker buoyancy, strong forcing
and an impressive kinematic space does hint that some stronger
updrafts within the line of storms appears possible which may pose a
strong to severe wind gust threat as it treks through northern UT.

Following the passage of the cold front, benign conditions look to
develop throughout the forecast area on Sunday and Monday as drier,
colder air fills in behind the front. Additionally, snow across
higher elevations of northern UT appears likely as snow levels drop
to around 7000ft. Chances for precipitation appear once again in the
extended on Tuesday as another upper trough looks to approach the
area, continuing our unsettled weather pattern.

&&

.AVIATION...KSLC...The SLC terminal will see VFR conditions
throughout the day. Southerly winds will become gusty at times by
early afternoon. Clouds will increase by early evening with a 30
percent chance of showers impacting the terminal after 00Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Increasing moisture will bring
increasing clouds and a threat of showers and thunderstorms over the
southern Utah airspace by late morning/early afternoon. The
moisture, and associated threat of convection, will spread northward
during the remainder of the afternoon and early evening, increasing
the coverage of showers and thunderstorms. Gusty and erratic winds
near thunderstorms along with localized MVFR to IFR restrictions are
the main hazards associated with any thunderstorms.

&&

.FIRE WEATHER...A widespread rainfall event is expected to develop
today lasting through Saturday evening. Throughout the duration of
this event, the majority of UT is expected to see a wetting rain.
Late Saturday, a cold front will sweep through the area bringing a
brief dry and cool pattern through Monday with an unsettled pattern
developing once again on Tuesday.

&&

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

WY...None.
&&

$$

PUBLIC...Worster
AVIATION...Traphagan
FIRE WEATHER...Worster

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