641
FXUS65 KSLC 191036
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
436 AM MDT Sun May 19 2024

.SYNOPSIS...Unsettled weather will continue through Tuesday, as the
next storm system brings increasingly cooler and wetter conditions.
A series of additional weak disturbances is then expected through
the remainder of the work week.

&&

.SHORT TERM (THROUGH 00Z WEDNESDAY)...The large-scale pattern this
morning has Utah returning to a southwesterly flow aloft as the next
trough carves into the PacNW. A couple of embedded features are
noted within this trough, with a vort lobe currently over eastern
Oregon while another is located just west of Vancouver Island.
Meanwhile, what is left of the previous boundary has lifted into
northern Utah, with remnant showers continuing through Utah County
and into the Uintas.

The next cold front associated with the upstream trough has already
moved through central Idaho and will be crossing northern Utah this
morning, reaching SLC around 15Z. Expect showers to continue to
develop near and ahead of this boundary today, with coverage
increasing somewhat through the day. Instability will remain fairly
modest, slightly less than yesterday, with the HREF ensemble mean
SBCAPE values remaining generally under 250 J/kg. Still, some
ensemble members are producing a smattering of 35+ dBZ cores in
simulated reflectivities, so isolated thunderstorms remain possible.
With the low levels still remaining relatively dry, the greatest
threat will continue to be isolated to widely scattered microbursts.
HREF probabilities show isolated areas with 10-20% chance of gusts
greater than 40 mph this afternoon.

The cold front is expected to stall and weaken over central Utah
this evening as the first embedded vort lobe ejects off into Montana
while the second feature continues to carve south. Southwest flow
will then continue to increase ahead of the boundary while a
reinforcing shot of cold air pushes into northern Utah tomorrow.
This will increase frontogenetic forcing along the boundary
tomorrow, which combined with increased moisture, will bring a
better chance of measurable precipitation, especially along the
boundary from southwest Utah through the Uintas. The trough will
then gradually swing through the forecast area through Tuesday,
maintaining cool and unsettled weather across the area. With H7
temperatures falling to between 0 to -3C by late tomorrow afternoon
(and slightly colder than than tomorrow night), snow levels are
expected to reach the high terrain, as low as around 7000ft over the
northern mountains. Presently, accumulations are expected to remain
relatively minor, although 6 inches or more over the high Uintas
will be possible. Otherwise, temperatures will see a noticeable
cooldown, falling well below climatological normals, especially
across northern Utah, Monday and Tuesday.


.LONG TERM (After 00Z Wednesday)...Long term forecast period starts
with a broad longwave trough extending throughout much of the W
CONUS, with an embedded shortwave impulse departing east of the
area. With this feature nearby (and depending on exact timing),
could maintain a few isolated showers early Wednesday mostly across
N UT and SW WY, but largely anticipate things to be winding down.
Following the departure of this shortwave, a brief period of zonal
flow to weak shortwave ridging looks to set in. This will result in
quieter/dry conditions for most of Wednesday, as well as
temperatures rebounding upwards several degrees with afternoon highs
near seasonal normal.

By Wednesday evening, the next shortwave impulse will be nearing the
forecast region as it digs through the longwave trough from the
PacNW. Initially, anticipate this will result in an increase in
isolated to scattered showers across N UT and SW WY. Thereafter
through Thursday, an associated cold frontal boundary will drop
southward into the forecast region, once again serving as a focus
for a bit higher precipitation chances. There remains some
differences in model guidance as to the exact amplitude and motion
of the parent shortwave, and thus how far south this cold frontal
boundary ultimately ends up progressing before stalling. Rough model
consensus at this point suggests near to maybe a bit north of the I-
70 corridor or so, which if valid would limit precipitation chances
across S UT. That said, a corridor of moderate H7 winds ahead of the
front will likely yield gusty surface winds in the 25-40 mph range
or so. Colder post-frontal conditions are also expected, with
temperatures behind the front falling around 5-10F or so, back to
well below climatological normal. Friday will remain a bit unsettled
as the trough lingers (with ~55% of ensemble members showing a bit
more of a weak trailing impulse), but generally expect a bit less
activity overall. Temperatures also remain around 5-15F below
seasonal normal for afternoon highs, though a good bit of spread is
noted (especially areas north) due to the aforementioned split on a
trailing impulse or not.

Moving into the weekend, uncertainty increases due to differences on
how guidance handles another shortwave digging a similar path
through the longwave trough. General ensemble consensus keeps the
feature far enough northwest that locally H7 temperatures increase
within deeper southwesterly flow, resulting in afternoon highs near
to a bit below normal. This would also keep things a bit less
unsettled, with some isolated to scattered showers, mostly diurnally
driven and favored over the high terrain from central Utah
northward. However, given the proximity to the shortwave and
associated features, will need to keep an eye on how guidance trends
in the coming days.


&&

.AVIATION...KSLC...Weak remnant boundary once again will yield
isolated high-based showers, but anticipate activity to generally
remain south of the terminal through the day Sunday. NW winds become
favored early (between ~13-16Z), and then should largely remain NW
thereafter. If any shower activity can form near the terminal, could
see some brief gusty and erratic outflow winds. SCT to BKN VFR cloud
cover maintained through Sunday. Sunday evening into the overnight
hours will see increasing shower chances as the next system begins
to approach.

.REST OF UTAH AND SOUTHWEST WYOMING...A fairly weak boundary will
remain draped across central Utah, and once again serve as the
primary focus for isolated high-based shower activity Sunday. Some
gusty and erratic outflow winds will be possible near these showers.
Otherwise, expect another day with a mix of generally mid to high
level VFR cloud cover. Shower chances then increase Sunday evening
into the overnight hours at northern terminals as the next system
begins to approach the area.


&&

.FIRE WEATHER...Ongoing showers across portions of northern/central
Utah this morning will continue through the day, gradually
increasing in coverage later in the day and overnight as the next
cold front pushes into Utah. This cold front will weaken over
central Utah tonight before another reinforcing boundary moves in
tomorrow, sweeping the front through the rest of the state through
tomorrow evening. Breezy to locally windy conditions can be expected
ahead of and near the front.

Showers today will continue to be generally high-based today,
producing generally small amounts of precipitation along with
isolated to widely scattered gusty microburst winds in excess of 40
mph. Moisture increases more for tomorrow, with greater chances of
wetting rain. However, portions of far southeast Utah will remain
dry and windy ahead of the cold front through much of the afternoon
tomorrow. As the parent storm system continues to slowly cross the
area, cool and unsettled weather will continue into Tuesday, with
the heaviest precipitation focusing over northeast portions of the
state. A brief break in the weather is expected for Wednesday before
another round of unsettled weather affects the area during the
latter part of the week.

&&

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

$$

Cheng/Warthen

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