806
FXUS65 KSLC 232145
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
345 PM MDT Sat Aug 23 2025

.SYNOPSIS...High pressure will continue to draw monsoon moisture
north into Utah and southwest Wyoming through the middle of the
upcoming week. This will bring increased coverage of showers and
thunderstorms, the potential for flash flooding, and gradually
less hot temperatures.

&&

.SHORT TERM...(Through 12Z/6AM Sunday)...As of early Saturday
afternoon, a mid-level high pressure ridge was centered over
southern Utah, and ample monsoonal moisture was in place beneath
the ridge. Precipitable water values now exceed 1"/175-200% of
normal across much of southern Utah. With the lack of large-scale
ascent, convective initiation is largely tied to terrain, and
slow-moving convection is gradually weakening as it moves off of
terrain and into adjacent valleys. However, new convective
initiation is likely to occur across areas that have yet to
receive convection where outflow boundaries collide. Given the
slow-moving nature of the convection and ample moisture in place,
there is a local flash flood risk, especially over burn scars,
areas of steep terrain, slick rock and normally dry washes, where
rainfall rates may approach 1.5" per hour. Also of note is an MCV
that is evident across extreme SE Nevada early this afternoon,
and many CAMs have initiated this feature and assimilated it into
their systems. Convection tied to this MCV can be tracked in
CAMs, moving northeastward across eastern Nevada early this
afternoon, before moving into west-central Utah through this
evening and across northern Utah tonight into Sunday morning. This
feature will act to aid in convective development and
maintenance, even after sunset.

On Sunday, convective initiation will once again largely be tied
to high-terrain areas, with one possible exception. A portion of
model guidance indicates the presence of another MCV moving across
southeast Utah Sunday afternoon, and this could enhance shower
and thunderstorm activity. This feature seems to be falling out of
recent model runs, so confidence is low on the potential
existence of this feature. In the absence of the feature, look for
terrain- based initiation once again Sunday. With the ridge
displaced a bit to the east, deep-layer flow will begin to become
southwesterly, and in the 10-20kt range, which will tend to favor
somewhat faster and less erratic storm motions Sunday. That said,
some erratic storm motions will still be encountered. One unknown
Sunday is whether or not the boundary layer will "recover" after
any morning shower/thunderstorm activity and associated MCV
subsidence/wake. If not, shower and thunderstorm activity may be
limited across northern Utah. Of course, if the MCV fails to
materialize at all, expect scattered, terrain-based showers and
thunderstorms. Enhanced deep-layer flow on Sunday will advect the
moisture-rich airmass across the remainder of northern Utah and SW
Wyoming so that the entirety of the forecast area will reside
within a moisture-rich environment. Therefore on Sunday,
strongest storms will be capable of heavy rainfall which could
lead to flash flooding, as well as gusty/erratic outflow winds,
especially near collapsing shower/thunderstorm activity.

.LONG TERM...(After 12Z/6AM Sunday), Issued 340 AM MDT... The mid
level ridge axis will slowly migrate into the southern
Rockies/southern Plains region during the early portion of the
upcoming week. Deep layer southerly flow along the upstream
periphery of this ridge will maintain a robust monsoonal airmass
across the forecast area through at least Tuesday, and likely
through Wednesday. Widespread PW values in excess of 1" and
surface dew points in the 50s across low-mid elevations will
provide ample moisture for showers and thunderstorms capable of
producing heavy rainfall through the first half of the week.
Ultimately mesoscale processes including MCVs will determine the
degree of instability and resultant convective coverage Monday
through Wednesday, but the potential for heavy rainfall and
attendant flash flooding will exist across the forecast area
during this timeframe.

It`s worth repeating that those with outdoor plans, as well as those
near flash flood prone areas such as normally dry washes, recent
burn scars, slickrock areas and slot canyons, should continue to
monitor the forecast and flash flood potential.

With this abundant moisture in place daytime temperatures will trend
lower through the first half of the week, running near climo Monday
before falling to 5-8F below climo by Wednesday.

A more westerly flow will become established for the latter portion
of the upcoming week, which will work to gradually erode the
monsoonal airmass. Lingering moisture will maintain showers and
thunderstorms, however coverage will decrease Thursday into Friday.
With the decrease in moisture temperatures are forecast to trend
slightly upward heading into next weekend.

&&

.AVIATION...KSLC...Northwesterly winds will likely continue, though
there remains a small chance that winds transition to southerly if a
stronger storm moves off the Oquirrh Mtns (20% chance). Otherwise,
southeasterly winds are likely to return around 03-04z. A few rain
showers may move over the terminal after 05z, with higher confidence
of light rain after ~12z. VFR conditions will prevail, though CIGs
may approach 7000-8000ft AGL with the aforementioned light rainfall.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms will continue through the afternoon and evening, with
the highest coverage over higher terrain. Showers may be capable of
producing gusty and erratic outflow winds up to around 25-35kts as
well as brief MVFR VIS. Showers will slowly trend downwards in
overall coverage during the overnight hours, but many locations will
still see light rain and even a couple lightning strikes. There is
some uncertainty with the development of a cluster of rain showers
Sunday morning across northern Utah. If this occurs (70% chance),
this would likely limit/inhibit storm development on Sunday
afternoon over northern Utah.


&&

.FIRE WEATHER...Monsoonal moisture is now firmly entrenched across
southern and central Utah, and this moisture will expand across
northern Utah through the weekend. Moisture will remain in place
through Wednesday or Thursday of next week, with dryer air by this
time forecast to overspread the area from south to north.
Initially, storms will be more of a mixture of wet and dry, then
trending increasingly wet through midweek. Shower and thunderstorm
initiation will be tied to terrain this weekend, with showers and
storms generally diminishing as they move off of terrain into
adjacent valleys, except where any outflow boundaries might
collide and create additional shower and thunderstorm activity.
With the increased moisture in place, expect increasing humidity
and decreasing temperatures through midweek. As is often the case
with scattered shower and thunderstorm activity, rainfall amounts
will likely vary widely over short distances. While wetting rains
are likely for most areas through the week, rainfall totals will
vary considerably. The heaviest showers and thunderstorms will
carry a risk for flash flooding, especially for burn scars and
steep terrain areas.

&&

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

$$

ADeSmet/Seaman/Cunningham

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