Round Valley, Utah Weather Forecast Discussion

717
FXUS65 KSLC 261022
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
422 AM MDT Fri Sep 26 2025
.SYNOPSIS...A slow moving cut-off upper level low will continue to
bring the threat of convection to southern Utah through Saturday,
expanding into eastern utah Sunday. A cold front is expected to
cross northern Utah Tuesday, with gusty southwesterly winds across
southern Utah ahead of the front.
&&
.SHORT TERM (Through 12Z Saturday)...As has been the case for the
last few days, the main story of the short term forecast period
continues to be a slow moving cut-off upper level low. Early
morning upper air and satellite analysis indicates the upper level
low is currently southwest of Las Vegas. Mesoanalysis indicates
precipitable water values have fallen from earlier peaks around
0.80" across southwestern Utah to around 0.60" or so.
CAMs have continued to shift an area of convection into
southwestern Utah this morning into early afternoon. Run after run
of the HRRR have suggested this area of convection will move into
lower Washington County after 16Z, whereas other CAMS suggest
after 20-21Z...or with some of the 06Z runs not at all. Subset of
the CAMS develop convection over the Pine Valleys during the
afternoon, with convection shifting down the instability axis into
lower Washington County after 22Z.
Regardless, SBCAPE values in excess of 1000 J/kg are forecast by
the bulk of the guidance this afternoon across southern Utah.
Unlike Thursday, deep layer shear is less pronounced, around 10 to
15 kts. This should keep most of the convection to a more pulse-
like morphology.
By Saturday morning, the cut-off low will be slightly eastward of
its position on Friday...with moisture advection ongoing once more
across southern Utah. Precipitable water values approaching 1" are
likely by Saturday afternoon. This combined with increased deep
layer shear, around 15-25 kts, will likely support stronger
convection across southern Utah Saturday afternoon and evening.
.LONG TERM (After 12Z Sunday)...Come Sunday, the cutoff low that
has been lingering over the Southwest will phase with the northern
stream over Utah and southwest Wyoming, becoming an open wave
that will help to kick off a round of precipitation that will
spread into central/ northern Utah and southwest Wyoming. As this
phasing occurs, a more significant longwave trough over the
northeastern Pacific will begin its push toward the U.S. West
Coast, and then inland early next week.
As the open wave passes through the region, cooler overhead
temperatures and cold pools produced by precipitation will help to
bring a decreasing trend with temperatures at the surface. The
cooling trend will be more pronounced across the southern half of
the area, where high temperatures will fall by around 5 degrees as
compared to the day prior, about 5-10 degrees below
climatological normals. Across the central and northern area,
highs will only fall by a few degrees and remain above normal
until the next day (when the cooler airmass has greater residence
time over the area). As far as precipitation goes, lower to mid-
level moisture will be paired nicely through the day which will
help to kick off diurnally driven convection over the higher
terrain of central and northern Utah. Meanwhile, southern Utah
will continue to see precipitation maintained in the early morning
hours as this region will coincide with the best synoptic-scale
forcing. This broader scale forcing will lift northward as the
wave progresses, aiding in further intensification of ongoing
precipitation across the northern half of the forecast area. With
the moisture profile in the low-to-mid levels remaining fairly
saturated, would anticipate another day of increased risk for
flash flooding in high risk areas (i.e. slot canyons, dry washes,
slickrock areas, and recent burn scars).
By Monday the aforementioned Pacific trough will be positioned
just offshore of the U.S. West Coast, placing Utah in a modestly
unstable southwesterly flow. Deterministic guidance is in strong
agreement of an ejecting shortwave trough translating through the
region late Monday through late Tuesday. As such, will see chances
for precipitation increasing through the second half of the day
on Monday and into much of Tuesday, primarily across the northern
two- thirds of the forecast area. This shortwave trough will usher
in a cold front to the northern area sometime Tuesday, though the
timing is a bit uncertain at this time. Because of the
uncertainty in the timing of the front, there is upwards of 10
degrees of uncertainty in the most likely (25th - 75th percentile)
high temperature forecast across northern Utah and southwest
Wyoming (upper 60s to upper 70s).
Beyond Wednesday there is some uncertainty with how the pattern
will unfold, namely with how quickly the offshore trough lifts
northward and whether or not a ridge of high pressure can
reestablish over a majority of the western U.S. A majority of
model guidance is in support of mid-level atmospheric heights
building through the remainder of the week (indicating a warming
and drying trend), however, there are about 10-20% of ensemble
members that maintain lower heights across the northern area
(potentially maintaining cooler and wetter conditions).
&&
.AVIATION...KSLC...VFR conditions are expected through the
forecast period with middle and high level cloud cover decreasing
through the late morning/ early afternoon. There is about a 20%
chance that area light showers move over the KSLC terminal before
14Z. Otherwise, expect southeast winds to transition to a
northwest wind around 19- 20Z, persisting through at least 03-04Z.
.Rest of Utah and Southwest Wyoming...VFR conditions are expected
outside of any shower and thunderstorm activity across the
southern half of the area today. Under heavier rain showers,
anticipate a reduction to MVFR to IFR conditions due to VIS
restrictions. Winds will be largely terrain driven outside of any
outflow wind gusts. A weak boundary is expected to push into
northwestern Utah late this evening, bringing a period of
northerly winds during the overnight hours in northwest Utah.
&&
.FIRE WEATHER...The slow moving cut-off upper level low will
continue bring a threat of thunderstorms each afternoon and
evening through the weekend. Initially thunderstorms will mainly
impact the southern half of Utah, spreading into eastern Utah
Sunday. Any thunderstorms will be capable of strong, gusty winds
and heavy rain.
A cold front is expected to cross northern Utah Tuesday. Ahead of
this front, expect gusty southwest winds, especially across the
southern half of Utah.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
Kruse/Webber
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NWS SLC Office Area Forecast Discussion