131
FXUS65 KSLC 181029
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
428 AM MDT Sat May 18 2024

.SYNOPSIS...An active, unsettled pattern will continue through at
least the first half of next week.

&&

.SHORT TERM (THROUGH 12Z MONDAY)...The shortwave trough the brought
the latest cold front into the area is now moving across the
northern High Plains while the next upstream trough is tracking down
the BritCol coast. The cold front associated with the departing
trough has made it to a Milford to Green River line, where it has
now stalled and continues to weaken. A few showers continue to
develop near the boundary, but remain very weak at this time.

Ahead of the next storm system, southwesterly flow aloft will begin
to return to Utah today, with the boundary slowly lifting back to
the north. Continued low-level convergence near this boundary will
maintain showers through the day and into the evening hours, with
increasing areal coverage as daytime heating commences. There has
been a slight upward trend in surface dewpoints, indicating a slight
moistening of the boundary layer. Despite this, most showers will
remain high-based, producing generally light precipitation with
isolated to locally scattered microburst winds. The HREF
probabilities show localized areas of 10-20% chance for winds of 40
mph or greater through this afternoon, with isolated areas of up to
40% in the Dugway Proving Grounds this evening. A few thunderstorms
will also be possible with the strongest storms, as HREF ensemble
means show small pockets of up to 500J/kg of SBCAPE this afternoon.

As the next upstream trough carves into the western CONUS tomorrow
into Monday, another cold front will shift south through Utah. This
cold front will be accompanied by more noticeably cooler air, along
with an uptick in moisture. As such, showers are expected to develop
again along portions of northern and central Utah tomorrow into
tomorrow night.


.LONG TERM (After 12Z/6AM Monday)...Long term forecast period begins
with a trough digging into the Great Basin, and an associated cold
frontal boundary slowly working southward through the local forecast
region. Near to slightly ahead of the frontal boundary, ensembles
generally show some agreement in PWAT values near to slightly above
climatological normal. With convergence along the boundary and
moderate synoptic support aloft with the trough, will see at least
some scattered showers and thunderstorms along/near the frontal
boundary. Thunderstorm potential will be slightly more noted in the
afternoon as daytime heating yields some pockets of low end
instability. Additionally, areas that remain ahead of the frontal
boundary into the early afternoon (southern Utah to southeastern
Utah) will see some moderate wind gusts (generally ~25-40 mph) given
decent pre-frontal deep layer southwesterly flow. Frontal boundary
will continue a southeastward trajectory out of the area moving into
Tuesday, but region will remain unstable enough within unsettled
cyclonic flow as the trough axis shifts overhead to yield continued
elevated precipitation chances through the day Tuesday. Overall QPF
doesn`t look too remarkable on a widespread level, but will likely
see some modest localized amounts where a more convective shower or
thunderstorm or two move through. The highest QPF totals look to be
through the Uintas, where snow levels are also forecast to drop
sufficiently to result in several inches of snow for the higher
elevations. While there`s still a bit of uncertainty in the overall
depth of the trough, post-frontal temps will drop quickly with
afternoon highs in most locations around 10-15 degrees below climo.

On Wednesday, guidance offers at least some slight consensus on a
quick shortwave ridge transiting the region (though ~20% of
ensembles maintain a bit more troughing). If this does indeed occur,
a period of quieter and more stable conditions can be expected, with
temperatures quickly rebounding back closer to normal.

Remainder of the forecast period carries greater uncertainty owing
to the exact positioning of a broader scale longwave trough across
much of the CONUS, and associated shortwave impulses rippling
through and potentially digging out higher amplitude sections of the
trough. Deterministic and ensemble members have varying scenarios in
regards to how deep the trough ultimately gets (and in turn any
frontal passages), as well as timing. A deeper trough would yield
higher chances of cooler/unsettled weather. Currently, ensembles
show around 60% of membership depicting of a deeper trough across
portions of the W CONUS on Thursday, and around 55% on Friday.
Ultimately though, some signal for an active northern stream remains
in most guidance. Will have to monitor how things ultimately trend,
but for now maintained NBM values which carry near to below normal
temperatures, as well as daily isolated to scattered precipitation
chances for the northern half of the forecast region where there`s a
better chance for the trough to impact.


&&

.AVIATION...KSLC...NW winds once again become favored after
17Z or so, and generally remain fairly light through the day. Winds
expected to flip back S around 03Z thereafter, though could see an
earlier flip if any shower activity south of the terminal produces
sufficient outflow winds. To that end, anticipate some potential for
isolated high-based showers late evening through the overnight as a
weak boundary lifts north, which will carry some threat for periods
of gusty erratic outflow with any showers near enough to the
terminal. Anticipate some increase in cloud cover as well, but with
conditions expected to remain VFR.

.REST OF UTAH AND SOUTHWEST WYOMING...A fairly weak frontal boundary
will lift north from central Utah towards northern Utah and
southwest Wyoming from late Saturday afternoon on into the overnight
hours. Anticipate some isolated to scattered high-based shower
activity as it does so, which will carry some threat of gusty
erratic outflow winds for any nearby terminals. With the showers
more high-based in nature, generally expect VFR conditions to
persist, though will see some increase in cloud cover for terminals
near the front.

&&

.FIRE WEATHER...A cold front has stalled this morning from around
Milford to Green River. This front will gradually lift back to the
north through the day today. High-based showers continue near the
boundary, and will continue to follow it north today while
increasing in areal coverage during the daytime hours. Measurable
rain chances have increased a bit for today, but wetting rain
chances remain generally low as many of the showers will be
relatively weak. That said, some of the stronger storms may result
in isolated to widely scattered thunderstorms. An isolated to widely
scattered threat of brief gusty and erratic microburst winds greater
than 40 mph remain in place for today.

The next storm system will gradually carve into the area tomorrow
through the early part of next week. An associated cold front will
cross Utah tomorrow into Monday, bringing cooler temperatures and
increased humidities to much of the area through at least Tuesday. A
break in the weather is expected on Wednesday, with the next
potential storm arriving during the latter half of the week.

&&

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

$$

Cheng/Warthen

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