Sevier, Utah Weather Forecast Discussion

707
FXUS65 KSLC 281031
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
431 AM MDT Sun Sep 28 2025
.SYNOPSIS...An upper level low will continue to eject northward into
early next week, maintaining unsettled conditions. A broader system
deepening into the Pacific coast then looks favored to shift inland
through midweek, and eventually push a cold front through the area
Friday into the weekend.
&&
.SHORT TERM (Through 12Z/6AM Tuesday)...Morning water vapor loop
shows a similar picture to that of this time yesterday with an upper
level low churning along the CA/AZ/NV border region. This low is
helping to pull moisture into the region, with synoptic support
maintaining some isolated showers. With some aid from associated
cloud cover, overnight temperatures are generally running around 5
to 10 degrees above normal.
Moving into the day Sunday, a broad longwave trough will gradually
amplify along the Pacific coast. This will help start tugging the
cutoff low northward towards the northern stream. Moisture with this
low will remain quite elevated, with PWAT anomalies around 150% to
200% across Utah and southwest Wyoming. Midlevel support especially
will increase as the system lifts northward, and HREF mean SBCAPE
looks to build into a broad general 200-500 J/kg range, likely with
some pockets of further enhanced instability where cloud cover is
more minimal. This combination will support increasing precipitation
development through the morning hours, with more convection then
expected through the afternoon. Given the abundant moisture and lack
of deep layer shear (only around 10 kts or so), once again
anticipate activity to primarily pose a localized excessive
rain/flash flood threat with anything moving/training over a rain
sensitive basin (recent burn scar, typically dry wash, slot canyon,
slickrock area). Local Flash Flood Potential Rating once again
carries widespread "Possible" ratings for area recreation zones, and
those considering venturing into such places should keep a close eye
on the evolution of the weather, and/or consider alternatives.
Activity will diminish in coverage and intensity as instability
decreases moving into the evening and overnight hours.
On Monday the cutoff low will continue to depart the region and
eject into the northern stream as more of an open wave. As it does
so the combination of mid level height rises and slightly drier air
will lead to a brief respite from at least more widespread active
conditions. Still, will see enough moisture/forcing to trigger some
afternoon convection that`ll tend to be more focused along the high
terrain. Moving into Monday night, a wave associated with the
broader deepening west coast trough will approach the region. This
will help to increase precipitation chances, especially for northern
Utah, as it does so.
.LONG TERM (After 12Z/6AM Tuesday)...Focus of the extended forecast
period will turn to a shortwave trough lifting through the northern
half of the forecast area which will favor precipitation across the
northern Utah mountains and valleys, as well as southwest Wyoming,
and introduce breezy southwest winds across central and southern
Utah. Thereafter there is a fair bit of model uncertainty revolving
around another potentially significant trough which will bring non-
zero chances for freezing temperatures in far northern Utah.
Key Messages:
- Precipitation will spread across northern Utah/ southwest Wyoming
from Tuesday morning through Tuesday evening, most likely brining
less than 0.5 inches of measurable rain to valleys and mountains.
- A weak cold frontal boundary will accompany the passing shortwave,
bringing cooler temperatures to northern Utah. South of about
Nephi, minimal changes in temperature are expected.
- Breezy southwest winds with gusts between 25-35 mph are expected
across central and southern Utah on Tuesday afternoon, mainly west
of the I-15 corridor.
By Tuesday morning, the axis of an ejecting shortwave trough off the
longwave trough in the northeast Pacific is progged to be located
just across the border in Nevada, placing northern Utah an a
favorable region for synoptic lift. This, combined with the moisture
tied to the wave, will act to kick off rain showers throughout the
day. Rain showers are expected to progress from far western Utah
early Tuesday morning into the Wasatch Front/ Cache Valley by the
early afternoon, and then into Uinta County, WY by the evening
hours. There has been a notable downward trend in precipitation
accumulation potential with these showers with current model
guidance showing little to no precipitation in the valleys to
upwards of 0.15-0.3 inches (25th-75th percentile). For the
mountains, as little as 0.01 inches (25th percentile) in the
northern Bear Rivers (zilch for the Wasatch and valley areas) to
around 0.2-0.3 inches across the mountainous terrain from the
southern Wasatch northward. In the lower likelihood scenario where
the shortwave comes in stronger (10% chance), rainfall totals could
amount to 0.25-0.5 inches for valleys and 0.5-0.75 inches for
mountains. Not an outstanding precip event by any means. For the
remainder of the area south of about Nephi, there is generally high
confidence that a dry forecast will unfold.
Cooler temperatures will accompany this shortwave, however, no
significant frontal passage is anticipated... moreso gradual
reduction of overhead (700mb) temperatures, particularly for the
northern half of Utah and southwest Wyoming. Cooling of upward of 5
degrees is expected for areas north of Salt Lake City, with little
to no cooling expected south of Nephi. Again, if this shortwave
comes through a little stronger we`ll see more appreciable cooling
for areas farther south... but this is about a 10% chance or less.
Otherwise, anticipate an uptick in southwest winds across the
southern half of the forecast area, primarily west of the I-15
corridor. Wind gusts of upwards of 25-35 mph can be expected during
the afternoon hours and shouldn`t bring any significant impacts.
Brief warming and drying of the airmass is expected Wednesday
through at least Thursday as we find ourselves on the western
periphery of a ridge. By Friday, uncertainty in the forecast
increases as the aforementioned longwave trough in the northeast
Pacific will attempt to pivot inland. Model guidance is hinting at
this system disconnecting from the northern jet stream, meaning that
we`ll likely just be ending up with the remnants of what once was a
strong, cold low pressure system. Current ensemble guidance only
shows about a 20-25% chance of this trough coming in stronger, with
the remaining ensemble suit favoring a less amplified trough with
lower chances for light precipitation across the northern area from
Friday through Sunday.
&&
.AVIATION...KSLC...VFR conditions are expected alongside south winds
throughout the valid TAF period. Afternoon showers are expected to
develop over nearby terrain and will have about a 30-40% chance of
directly impacting the airfield. The most likely impact due to these
showers will be outflow winds producing a westerly crosswind between
20Z to 00Z. Otherwise, expect CIGs to remain at, or above, 8kft AGL.
.Rest of Utah and Southwest Wyoming...Areawide showers and
thunderstorms are expected through much of the day today, with
coverage becoming maximized during the afternoon hours. VFR
conditions are expected across a majority of the area, however, CIGS
around 7-8kft AGL may obscure the higher terrain features across the
region. Under heavier rainfall, reduction to MVFR to IFR conditions
will be possible due to reductions in VIS. Outside of any outflows,
winds will be favored out of the southerly direction around 10kts.
&&
.FIRE WEATHER...An area of cutoff low pressure is continuing to slowly
lift through the region overnight. This will continue to
influence the area with areas of scattered showers and
thunderstorms developing through the day Sunday. In addition to
periods of moderately heavy rain and lightning, stronger storms
will have potential to bring modestly strong erratic outflow wind
gusts up to around 40 mph or so. This low will start to lift out
on Monday, with a drying trend noted and more isolated activity
tending to be more focused along/east of Utah`s high terrain.
Moving into midweek a broader system will begin to deepen into
the western U.S. An embedded impulse within this along with
moisture will brush by Tuesday, bringing renewed precipitation
chances especially to northern Utah. Additionally, flow with the
broader system will start to modestly enhance gusts, supporting
some localized areas of elevated fire weather conditions where
fuels remain sufficiently dry. Drier conditions then set in
briefly, with models generally supporting the inland motion of the
broad system eventually pushing a cold front through the area
around Friday into the weekend. This front will have potential to
bring a more notable cooldown in its wake.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
SHORT TERM...Warthen
LONG TERM...Webber
AVIATION...Webber
FIRE WEATHER...Warthen
For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

NWS SLC Office Area Forecast Discussion