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282
FXUS65 KSLC 171018
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
418 AM MDT Tue Sep 17 2024

.SYNOPSIS...
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A fall storm system will bring much cooler
temperatures across the region, along with unsettled weather
across northern Utah. Cool and unsettled weather will continue
across the region through the remainder of the week.
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.SHORT TERM (Through 12Z Thursday)...
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An upper low is slowly
lifting through the northern Great Basin early this morning, with
the associated north-south oriented low level baroclinic zone
bisecting Utah. A shortwave trough rounding the base of this upper
low is rotating through the southern Great Basin, and will
quickly lift northeast through the forecast area this morning.
This feature working along the baroclinic zone is resulting in
fairly widespread precipitation across northern/central Utah,
with additional showers developing just ahead of this approaching
shortwave. This precip will persist through the morning hours as
the aforementioned wave lifts north, eroding from south to north
through central Utah in the wake of this feature. By early
afternoon synoptically forced precip will largely be confined to
the Idaho border region, with scattered afternoon convection
across the remainder of northern Utah under the upper cold pool.
Snow levels falling to roughly 9000 feet will result in some light
snow accumulation along the upper elevations of the Wasatch along
with the western Uintas.

Much cooler air combined with considerable cloud cover will keep
temperatures confined to the 60s across northern valleys, as well
as lower elevations of central and southwest Utah excluding St
George. This is roughly 15F below climo, and a stark contrast to
the late summer-like temperatures observed recently. In the wake
of the departing upper low, this cool and stable airmass will
remain in place across the forecast area through Wednesday,
keeping max temperatures nearly 10F below climo. Typically colder
locations such as the Wasatch Back, Bear River Valley and areas
around Loa may see temperatures approach the freezing mark the
next couple of nights.

.LONG TERM (After 12Z Thursday)...Guidance has trended slightly
drier and warmer for the long term period as the trough that moves
into the Great Basin on Thursday begins to cut off and weaken as it
moves further inland. Shortwave ridging will amplify on Thursday
ahead of the trough as it`s positioned over central California. This
will keep conditions mostly dry with little cloud cover on Thursday
as most of the precipitation associated with the low remains over
Nevada and California. Additionally, high temperatures will rebound
closer to normal on Thursday with mid to upper 70s across most
valleys and mid 80s for far southern Utah.

As the trough shifts east on Friday the upper level low likely
becomes cutoff while filling in and weakening. With the center of
the low moving across northern Arizona, precipitation will be more
likely across central and southern Utah, but weak ascent will limit
the precipitation totals to generally less than 0.1". Temperatures
will cool a few degrees across the southern half of the CWA, but
remain largely unchanged across northern Utah/SW Wyoming given the
further proximity to the center of the low pressure system. This low
shifts further east on Saturday with a few diurnal showers possible
across eastern portions of the CWA.

After this low exits the region we will be left in a weak northwest
flow that will keep temperatures near normal for this time of year
making for optimal fall foliage peeping weather over the weekend.
Given the weak northwest flow regime we will be left in, guidance is
a bit indecisive on whether we introduce another trough (~23% of
members) or if we move into more of a ridging pattern (~77% of
members).
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.AVIATION...
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KSLC...VFR conditions will persist for the KSLC terminal
through the period. An upper level low will be centered over the
airspace today resulting in light rain showers in the morning
shifting to more of a convective regime in the afternoon. Lowered
CIGs will result in some mountain obscuration, at times. Winds will
predominantly be out of the north/west.

.REST OF UTAH AND SOUTHWEST WYOMING...An upper level low centered
over the northern airspace will result in light showers in the
morning evolving into convection in the afternoon. Lowered CIGs will
result in a mix of VFR/MVFR as well as mountain obscuration. Across
the south, prefrontal winds will gust out of the southwest with dry
VFR conditions.
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.FIRE WEATHER...
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A low pressure system will cross the region
today, bringing rain and high elevation snow showers to much of
northern Utah. Much cooler air associated with this system will
trend temperatures 15-20 degrees cooler across northern Utah this
afternoon, and 6-10 degrees cooler across the south. Drier air
will remain across southern Utah, and with gusty southwest winds
developing across zones 489, 494 and 498 this afternoon, near
critical fire weather conditions are expected. This cool airmass
will remain in place through much of the remainder of the week,
with another low pressure system bringing unsettled conditions
during the latter portion of the week.
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.SLC WATCHES/WARNINGS/ADVISORIES...
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UT...None.
WY...None.
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$$

Seaman/Mahan

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