Starr, Utah Weather Forecast Discussion

907
FXUS65 KSLC 201021
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
421 AM MDT Sat Sep 20 2025
.SYNOPSIS...An unsettled weather pattern will remain in place across
northern Utah through Monday as a series of weather systems cross
the area. A drying trend is expected to develop by Tuesday.
&&
.SHORT TERM (THROUGH 00Z TUESDAY)...Remnants of a weakening trough
will continue to lift northeast across Utah this morning. This will
continue to bring increased moisture into northern Utah while
southern Utah will dry somewhat. Latest analysis shows PWATs of
generally 0.7-0.8 inches across most of the area, with a small area
of closer to 1 inch across far southwest Utah. A few showers have
persisted overnight across northern Utah owing to this moisture and
aforementioned weak forcing.
With the onset of peak daytime heating, expect weak showers to
transition more to stronger convection this afternoon. Focus will
remain over the north, with more isolated coverage and generally
weaker convection over the south due to the lack of any real forcing
mechanism there. Storms may initially remain high-based and produce
gusty outflow winds before gradually trending more wet. However,
with dewpoints now having risen to the mid to upper 40s across much
of northern Utah (upper 30s along the Idaho border), any outflow
winds should not be especially strong. The HREF ensemble max wind
gusts fail to show anything reaching 50 mph through this evening.
Overnight, a subtle shortwave disturbance is progged to ripple
through far northern Utah. This may maintain some nocturnal showers
(and perhaps few thunderstorms) once again over portions of northern
Utah.
Sunday afternoon should feature a ridge largely building back into
the area. While the midlevels are expected to dry a bit, enough
lingering low-level moisture will pair with daytime heating to
result in another round of convection across the north, initiating
off the higher terrain. By late afternoon, a shortwave trough
dropping into Idaho from the PacNW may allow convection to develop
more into a loosely organized line which will cross northern Utah
during the evening hours. This will be followed by a cold front
which will push into northern Utah overnight. With the trough
pinching off into a closed low over Wyoming and continuing to carve
into northeast Utah and southwest Wyoming, expect showers and
thunderstorms to continue at least across portions of eastern Utah
and southwest Wyoming through the day Monday.
.LONG TERM (After 00Z Tuesday/6 PM Monday)...Increased dry,
northerly flow aloft associated with a grazing shortwave trough will
result in temperatures dropping several degrees below seasonal
normals across northern Utah and southwest Wyoming on Monday.
Otherwise, relatively benign and seasonable weather is expected
areawide through Tuesday as a drier airmass overspreads the region.
The aforementioned trough continues to move eastward out of the
region on Tuesday, eventually phasing into a longwave trough over
the MS River Valley. Our area becomes wedged between this feature
and a closed low off the coast of southern California mid-week. The
forecast becomes quite uncertain Wednesday onward given the model
discrepancies in the track of the closed low. Ensembles are in a
roughly 50/50 split on potential scenarios. One solution takes the
low inland Wednesday into Thursday, bringing with it tropical
moisture that would support wetter weather returning as early as
Wednesday. The other solution keeps this low offshore until late
Thursday, before moving inland on Friday. This solution would keep
us drier on Wednesday and Thursday, with better chances for showers
and storms on Friday into the weekend.
&&
.AVIATION...KSLC...VFR conditions continue at the terminal through
the period, with continued SCT-BKN mid-level cloud cover. Winds
remain light out of the southeast, transitioning northwesterly after
20z. There is a 30% chance for thunderstorms to impact the terminal
between roughly 21-00z today, with another round between roughly 04-
09z Saturday. Any storms that develop this afternoon will be capable
of producing gusty and erratic winds in addition to frequent
lightning.
.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions continue
through the period for all regional terminals. Some isolated showers
are possible for Wasatch Front terminals early this morning, though
chances remain less than 30%. Another round of afternoon convection
is expected today, with coverage mainly favoring the northern
portion of the airspace. Any storms that develop this afternoon will
be capable of producing gusty and erratic winds in addition to
frequent lightning.
&&
.FIRE WEATHER...Moisture remaining in place over the area will allow
for scattered showers and thunderstorms into Monday, primarily over
the northern half of Utah where a series of weather disturbances
continue to cross the area. Although wetting rain chances are not
especially high, with the lower levels moistening, some of the
stronger storms will be capable of producing wetting rain.
Otherwise, some of the initial storms today could be fairly dry and
produce gusty outflow winds.
Cooler temperatures will spread into Utah for Monday behind a cold
front, with the airmass then trending drier as well. This drying
trend will continue into at least Tuesday. Thereafter, a low
pressure system meandering over the West Coast will eventually
approach Utah, potentially as early as Wednesday but more likely
later in the week. When it does so, it will bring another period of
unsettled weather to the area.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
Cheng/Whitlam
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NWS SLC Office Area Forecast Discussion