895
FXUS65 KSLC 212128
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
328 PM 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)...Moisture continues to
stream into the area from the south along the western periphery of
high pressure, as seen on satellite imagery this afternoon. As
such, showers and thunderstorms have developed this afternoon,
particularly further south. Observed outflow winds have reached
up to around 40-50 mph across southern Utah, with MRMS rainfall
estimates up to 0.50" across slower-moving or training storms.
Across the north however, morning showers likely used up a lot of
the instability, so showers have been weak at best with only very
isolated thunder/lightning. Convection will gradually dwindle
through the evening, with scattered mid-level clouds lingering
through the overnight hours, mainly across northern Utah.

Showers and thunderstorms will develop once again tomorrow
afternoon, and given increasing mid-level moisture atop of still
dry low levels, the threat of dry microbursts will return. Storms
look a bit more potent tomorrow yet still slow-moving, with a
slightly increased threat of gusty outflow winds. The 12z HREF max
wind gust field highlights primarily southeastern Utah with a few
isolated areas of up to 55 mph winds.

Temperatures will continue to increase slightly over the next
couple of days as high pressure builds overhead. Thus, Extreme
Heat Warnings have been continued through tomorrow evening for
Lower Washington County and Zion National Park, given highs well
into the 100s and lows only reaching the upper-70s to low-80s.

.LONG TERM (After 12Z/6AM Saturday), Issued 355 AM MDT...
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 will persist for the KSLC terminal
through the period. Some evening VIRGA with dry conditions and
scattered mid level clouds will continue with diurnally driven winds.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist
for the airspace through the period. Mountain convection will
dissipate across the southern mountains with scattered mid level
clouds and VIRGA this evening elsewhere. Otherwise, conditions will
stay mostly dry with diurnally driven winds.

&&

.FIRE WEATHER...Increasing monsoonal moisture statewide will be the
main story of the entire 7 day period, with a secondary surge of
moisture arriving Sunday. Coverage of showers and thunderstorms
will therefore gradually increase each day, with an associated
increase in cloud cover, especially after Sunday. While gusty and
erratic outflow winds are the main threats for today and tomorrow,
as moisture increases and storms trend wetter, expect increasing
chances for wetting rains instead. Additionally, minimum and
maximum RH will increase by around 10 percent between Sunday and
Monday as that secondary surge moves in, with still a gradual
increase thereafter. Model guidance suggests the moisture peaks
around Wednesday, though this may still vary moving forward.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Extreme Heat Warning until 9 PM MDT Friday for UTZ123-124.

WY...None.
&&

$$

Cunningham/Whitlam/Wessler

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