541
FXUS65 KSLC 202210
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
410 PM MDT Wed Aug 20 2025

.SYNOPSIS...While high pressure will bring anomalous heat into the
start of the weekend, a marked monsoonal moisture surge looks to set
in and bring a change to a cooler and wetter pattern.

&&

.DISCUSSION...Afternoon water vapor imagery shows an expansive ridge
of high pressure more of less centered atop the Four Corners
region. While the ridge is resulting in yet another anomalously
warm day at most locations around the region, it is positioned in
such a way that some modest return of mid level moisture is noted.
In turn, area radars picking up on some fairly faint echoes of
what is largely some modestly high based showers. Haven`t seen
this translate into much of the way of strong wind gusts yet, but
with DCAPE sitting around 1000-1300 J/kg across much of western
Utah, wouldn`t entirely discount it.

Through the remainder of the work week, the strength and position
of the ridge will allow for a continuation of the ongoing
anomalous warmth. This will be most noted across southern Utah
where mild overnight lows will increase the combined HeatRisk.
This was most noted across portions of lower Washington County and
lower elevations of Zion NP, and given the combination of
increased population and recreation in particular, have maintained
the ongoing Extreme Heat Warning for Thursday and Friday.

In addition to the heat, the position of the ridge will allow for
the continued advection of moisture into the area. The gradual
moistening will push PWATs to around 100-150% of climatological
normal for late August, supporting increasing daily shower and
thunderstorm chances into the weekend. Coverage of activity is
expected to be most widespread across portions of southern Utah
and elsewhere along/adjacent to high terrain, though will see some
better coverage expanding northward day to day as moistening
continues. Given this, The Weather Prediction Center continues to
highlight southern Utah for a Marginal (level 1 of 4) risk of
excessive rainfall through Saturday. Correspondingly, local Flash
Flood Potential Index carries increasing levels of "Possible" for
area parks. In general, flash flood threat will be most
pronounced at more rain sensitive locations such as recent burn
scars, slot canyons, typically dry washes, and slickrock areas.
Those planning any recreation to such areas will certainly want to
remain weather aware.

Sunday on into at least the early portion of next week will see
the monsoonal moisture surge increase as the ridge starts to
shift, with widespread PWATs shifting to around 150-200% of
climatological normal. In turn, coverage becomes increasingly
widespread areawide, and the risk of excessive rainfall is
maintained and expanded. One question that`ll be difficult to pin
down until later on is how the coverage of any nocturnal activity
and associated cloud cover influences diurnal destabilization and
subsequent convective evolution through the day. Moisture will
certainly be plentiful by this point for what convection manages
to form, but have seen times where the abundance can result in a
more stable/stratiform regime dominating on a more widespread
scale. All the same, those planning any sort of recreation to
those aforementioned rain sensitive areas will certainly want to
keep an eye on the weather. Aside from the moisture, the ridges
position in combination with convection/cloud cover will allow a
noticeable trend downward to daytime temps, with forecast carrying
widespread values around 5-10F below normal by Tuesday.

&&

.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...Expansive high pressure situated near the Four Corners
region is continuing to result in very mild temperatures. Small
quantities of moisture are starting to work in around this high
pressure ridge, resulting in some high based showers across
western Utah. Given the higher based nature, these showers will
primarily carry a threat of gusty and erratic outflow winds.

Moisture will continue to increase Thursday onward as a more
marked monsoonal surge begins in earnest. Afternoon showers and
thunderstorms will start to become more widespread, wetter in
nature, and associated humidity values trend upwards. Coverage
will especially increase in coverage Sunday into early next week
as the moisture becomes maximized. This expansion to precipitation
will also result in a more noted trend downward to temperatures
and trend upward in humidity.

&&

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

WY...None.
&&

$$

PUBLIC...Warthen
AVIATION...Mahan
FIRE WEATHER...Warthen

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