Duchesne, Utah Weather Forecast Discussion

976
FXUS65 KSLC 202143
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
343 PM MDT Sat Sep 20 2025
.SYNOPSIS...An unsettled pattern persists into early next week along
with a cooldown at many locations following the passage of a cold
front. Drier conditions are then expected through midweek, with
some moisture starting to return late in the work week
&&
.SHORT TERM (Through 00z Tuesday)...A remnant trough continues to
slowly lift through overhead this afternoon. This feature is
helping to maintain a fairly moist environment, with PWAT values
around 150% to 200% of climatological normal. This in combination
with ongoing destabilization is resulting in isolated to scattered
convective development across the area, especially at locations
further north where the aforementioned trough is helping provide a
little more lift. That said, lingering cloud cover from the
morning has resulted in a more gradual increase in instability,
though satellite trends show more breaks starting to develop. As
such, think the HREF 25th- 75th percentile range of SBCAPE around
100-500 J/kg seems reasonable. With the extra moisture and higher
dew points, LCLs are around 1000 to 2000 m, and DCAPE values are a
bit meager. While a stronger storm or two may be able to produce
some modestly gusty outflow winds still, thinking the threat of
gusts in excess of 50 mph or so is pretty low. With the moister
environment and somewhat slow storm motion, periods of moderately
heavy rain (in addition to lightning) seem to be the biggest
threat today. Coverage and intensity of activity will decrease
with loss of heating through the evening hours, but sufficient
upper level support will remain to yield some nocturnal shower
chances across northern Utah and southwest Wyoming.
On Sunday a trough will advance towards the region while a cutoff
low remains more or less positioned near the southern California
coast. While a brief period of transient ridging may be realized
early, sufficient moisture in combination with the approaching
trough looks to trigger shower and thunderstorm development
through the day. With mean SBCAPE increasing across the northern
half of the forecast region and a bit more deep layer wind shear,
wouldn`t be surprised to see a more organized updraft or two
develop. Sunday evening into the overnight hours the trough will
push a frontal boundary southward into the area. As such, may see
a bit more linear/organized feature try to develop along this
boundary as it pushes in, and will actually see precipitation
chances increase.
Moisture will begin to decrease from west to east through the day
Monday as the trough starts to cut off near the UT/WY border. In
turn, isolated to scattered convective chances become more focused
along/east of Utah`s high terrain. Otherwise, biggest noticeable
change to weather will be in the form of a cooldown on the order
of several degrees at areas behind the front. Anticipate afternoon
highs around 3-7F below normal at these locations, which
translates to mid 60s across SW WY and low to mid 70s across much
of the Wasatch Front.
.LONG TERM (After 00Z Tuesday/6 PM Monday), Issued 421 AM MDT...
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 will persist for the KSLC terminal
through the period. Convection, mostly tied to the terrain, will
gradually diminish through the evening with isolated showers
overnight. These showers will interrupt the diurnal winds before
predominant southerly flow sets up overnight.
.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist
for the airspace through the period. Terrain-driven diurnal
convection across the north could briefly impact a terminal with
some gusty outflow winds or lightning. These will gradually diminish
overnight with isolated showers remaining possible overnight.
Overall, winds will be light and diurnally driven.
&&
.FIRE WEATHER...The influence of a lingering upper level disturbance
along with ample moisture is resulting in scattered showers and
thunderstorms, especially across northern Utah. Given continued
support through the overnight hours, some chance of nocturnal
showers and a thunderstorm or two will persist. A similar
convective evolution is expected Sunday, with morning activity
becoming increasingly convective in nature, primarily across
northern Utah where moisture and forcing for ascent will be
maximized. Late Sunday evening into the overnight hours a cold
frontal boundary will drop southward into Utah. This will maintain
precipitation chances overnight, with potential for more of a
linear type of storm mode to form along the boundary. Following
the passage of the front, temperatures cool markedly. The airmass
will also begin to dry from west to east, with precipitation
chances Monday becoming increasingly focused along/east of Utah`s
high terrain.
Drier and less active conditions are expected to settle in
through the middle of the week as high pressure becomes more
favored. While lower confidence is noted in specifics at this
time, models then suggest moisture will return with a slow moving
cutoff system advancing into the region late in the work week into
the weekend.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
SHORT TERM...Warthen
LONG TERM...Whitlam
AVIATION...Mahan
FIRE WEATHER...Warthen
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NWS SLC Office Area Forecast Discussion