771
FXUS65 KSLC 282124
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
324 PM MDT Sun Apr 28 2024

.SYNOPSIS...Utah and southwest Wyoming will see mild and breezy
conditions during the day Monday before a cold front moves through
late Monday into early Tuesday, bringing cooler temperatures and
some showers to northern portions of the area. Another mostly dry
cold front is expected to impact the area midweek.

&&

.SHORT TERM (through 12Z/6AM Tuesday)...West to northwest flow has
brought some modest warm advection to Utah and southwest Wyoming
this afternoon. As a result, maxes are averaging 5-7F above what
they were yesterday, within 5F of seasonal normals. Other than a
few light popcorn showers over northern Utah, conditions are
fairly benign over the area. Any lingering showers should diminish
early this evening.

As the work week begins, attention turns to a trough forecast to
move onshore along the Pacific Northwest coast tonight until
tomorrow morning. There is high confidence that this system will
track east during the day, grazing northern Utah late Monday
afternoon into early Tuesday. The trough looks to be relatively
moisture starved, but northern Utah should still see some showers
during the afternoon and evening, as instability is somewhat
favorable. Any accumulations will be light and confined to the
higher elevations.

The front will bring a greater impact to northern Utah
temperatures, which are expected to run up to 10F above climo on
Monday. The passage of the front is expected to drop those maxes
back to near seasonal normals by Tuesday. A tightening pressure
gradient ahead of the front will lead to some breezy winds, and
would not be surprised to see some gusts in excess of 40 mph just
ahead of the frontal passage, most likely over northwest Utah.
However, anticipated flow aloft does not support widespread or
long lasting gusts in excess of Wind Advisory criteria, so have
held off on any headlines at this time.

.LONG TERM (After 12Z/6AM Tuesday)...

...Cool through mid-week then warming trend by the weekend...

Tuesday through Thursday will be dominated by an active pattern
across the Northern Rockies as a low pressure system remains over
Montana. Northern Utah in particular will feel the influence of this
troughing to our north, while southern Utah largely remains south of
the boundary stalled across the state.

Looking at the specifics, there is high confidence in a shortwave
trough grazing northern Utah Monday night, which will be quickly
departing to our east by Tuesday. The resulting cold advection and
subsidence behind the shortwave passage will support a cooling
temperature trend across northern Utah, while also acting to produce
dry and mostly clear conditions (mainly early in the day). However,
cloud cover will start to increase again across northern Utah later
Tuesday ahead of the next wave to impact the region. Meanwhile,
southern Utah on Tuesday will remain south of the stationary front
and will see steady to slightly warmer temperatures than Monday.

By Wednesday, confidence among ensemble members is increasing about
bringing a trailing shortwave pinwheeling southward around the
influence of the low centered over Montana. This will swing a deeper
trough axis into Utah on Wednesday, however, the magnitude of its
depth now remains the primary point of contention among the
ensembles - with the main consequence being how far south the cold
front makes it across Utah. Now approximately 75% of ensembles have
a slightly more robust trough which will eventually push the cold
front into southern Utah - of these 75% a little less than half have
a slower and even deeper solution that would hold the cold air off
until later Wednesday into Thursday. Otherwise, only approximately
25% of ensembles have a shallower trough which stalls the frontal
boundary across central Utah resulting in milder temperatures remain
in place across southern Utah. Otherwise, while some showers will
accompany this trough, it will be a relatively dry system. Only
about 10% of solutions produce more than 0.1" of water in the
valleys and more than 0.25" of water in the mountains, all mainly
across northern Utah. Much of southern Utah has a high chance of
staying completely dry.

Late week into the weekend, there is increasing confidence in a
warming trend, although the exact details of the large scale pattern
evolution are a little dicey yet. However, the main trend in the
ensemble solutions into the weekend is for a weak ridging to build
particularly down stream of the forecast area. There remains some
solutions that are a bit slower to evolve this pattern, but by
Sunday every cluster supports this downstream ridge with a building
thermal axis over Utah now. For KSLC, there is an 80-85% chance of
exceeding 70 degrees by Saturday and Sunday. For St George, there is
a 60% chance of exceeding 85 degrees Saturday and Sunday.

&&

.AVIATION...KSLC...Trailing energy from departing system to maintain
some VFR cloud cover and limited chance (less than 20%) of isolated
showers through Sunday evening. Diurnally typical winds expected,
with switch to S drainage flow between ~03Z-05Z, and a return to NW
flow between ~18z-21z Monday. Another passing impulse will yield
some isolated shower chances Monday afternoon which could result in
brief variability to winds in addition to slightly degraded
conditions at the terminal, but largely anticipate VFR to prevail.

.REST OF UTAH AND SOUTHWEST WYOMING...At northern terminals, a few
isolated showers possible through this evening, but expect VFR
conditions to prevail. A relative lull is then anticipated
overnight, but another quick and fairly weak impulse will trigger
some isolated to scattered shower activity during the day Monday.
Even then, largely expect VFR conditions outside of any heavier
showers. At southern terminals, clearer skies and VFR conditions
anticipated. Areawide winds will largely follow something of a
diurnally typical pattern, though could see passing showers at
northern terminals yield some slight variability at times.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

SHORT TERM...Traphagan
LONG TERM...Church
AVIATION...Warthen

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