557
FXUS65 KSLC 210955
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
355 AM MDT Thu Aug 21 2025

.SYNOPSIS...With high pressure centered over the Four Corners,
monsoon moisture will gradually spread northward into Utah and
southwest Wyoming through early next 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 Saturday)...Utah and southwest
Wyoming is under a southerly flow this morning on the back side of
a ridge centered over the Four Corners region, a classic setup
this time of year for the northward advection of monsoon moisture.
For now, skies are mostly clear with the exception of some clouds
and a few showers along a weak boundary over northwest Utah. This
boundary will gradually retreat to the northwest this morning,
with light showers continuing to remain possible along it. Highs
will be a bit less hot than yesterday, but will still average
around 5F above seasonal normals. Temperatures will be most
abnormally hot for lower Washington county as well as Zion
National Park, where an Extreme Heat Warning remains in effect
through Friday.

Moisture will continue to spread northward today, with PWs
expected to be in the 0.8 to 0.9 inch range across much of the
area this afternoon. This will bring a noticeable increase in
coverage of afternoon and early evening showers and thunderstorms,
especially for the higher terrain of southern Utah. Given the
recent dry conditions, moisture will initially be confined to the
high and mid levels, so will continue to see a threat of gusty
microburst winds with any storms that develop today.

Moisture will continue to creep northward for Friday, with PWs
across parts of southern Utah forecast to rise to above 1.0 inch
by Friday afternoon. Thus, coverage of convection will increase
further, with a greater potential for wetting rains and flash
flooding, especially for southern Utah.

.LONG TERM (After 12Z/6AM Saturday)...Deep monsoonal moisture will
continue to advect into the region on Saturday, especially across
southern and central Utah. This will allow storms to trend wetter,
thus bringing an increased risk for flash flooding across the
aforementioned areas. Thus, the Weather Prediction Center has
expanded the Marginal risk (level 1 of 4) for excessive rainfall
further northward into central Utah for Saturday.

The monsoonal moisture surge becomes especially pronounced over the
region by Sunday and into early next week, with PWAT anomalies
increasing to around 150-200% of normal across all of Utah and
southwest Wyoming during this period. Expect more widespread shower
and thunderstorm coverage as a result, with the Weather Prediction
Center maintaining the Marginal risk of excessive rainfall across
the entire region through at least Monday. As we head into early
next week, the main forecast question will be if this anomalous
moisture produces enough nocturnal activity and associated cloud
cover, which would inhibit afternoon convection and support a more
stratiform precip regime. Regardless, those with outdoor plans this
weekend and early next week should stay tuned to the forecast as
flash flooding remains a threat. Locations with greatest threats for
flash flooding include slot canyons, normally dry washes, slickrock
areas, and recent burn scars.

In addition to widespread precipitation chances, this monsoon surge
will promote gradual cooling this weekend and into next week. Near-
average temperatures this weekend are expected to give way to highs
around 5-10 degrees below average by mid-next week.

&&

.AVIATION...KSLC...VFR conditions to persist at KSLC through the
period. Light southeasterly winds this morning transition
northwesterly around 16z. Some high-based showers are possible this
morning between roughly 16-17z, mainly producing virga. An
additional round of high-based showers are possible this afternoon
between roughly 20-23z, with ~30% chance to produce lightning and
erratic winds in the vicinity of the terminal.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions to continue for
all regional terminals through the period. Winds remain generally
light and diurnally driven. A couple rounds of precipitation are
expected across the airspace today, first with a band of scattered
high-based showers traversing northern Utah mid-morning, then with
convection developing over the high terrain this afternoon.
Afternoon convection will be capable of producing lightning and
erratic outflow winds.

&&

.FIRE WEATHER...High pressure remains centered over the Four
Corners, where it will remain for the next several days. This will
keep southerly flow over Utah that will draw monsoonal moisture
northward. Coverage of showers and thunderstorms will increase
noticeably today, particularly over southern Utah. However, given
that the moisture will initially be high based, chances of
wetting rains will be relatively low. As the moisture continues to
increase for the weekend and into early next week, wetting rains
will become more likely as coverage of storms continues to
increase. The increase in moisture will also bring a gradual
decrease in temperatures, with highs falling to or below seasonal
normals by early next week. Away from thunderstorms, winds will
remain generally light and terrain driven over the next few days.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Extreme Heat Warning from noon today to 9 PM MDT Friday for
     UTZ123-124.

WY...None.
&&

$$

SHORT TERM/FIRE WEATHER...Traphagan
LONG TERM/AVIATION...Whitlam

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http://weather.gov/saltlakecity