737
FXUS65 KSLC 182059
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
259 PM MDT Sat May 18 2024

.SYNOPSIS...A spring-like storm Sunday night into Tuesday will
bring cooler and wetter conditions. A series of additional weak
disturbances is then expected through the remainder of the work
week.

&&

.SHORT TERM...A mid-level boundary stalled over southern Utah has
been slowly lifting into central Utah this afternoon and will
continue its northward track into northern Utah and southwest
Wyoming by this evening into early overnight. Convection is
associated with this boundary, and can easily be identified on
satellite imagery stretching from roughly Enterprise to
Hanksville as of this writing. CAMs show minimal CAPE but some
available shear, while surface analysis reveals dry sub-cloud
conditions with dewpoints sitting around 30 degrees. Given these
conditions, precipitation is having difficulty reaching the
surface, and the primary hazard remains gusty outflow winds, with
stronger cells having a 50% chance of lightning as well.

Latest CAMs track this activity (high-based showers and
thunderstorms) into the southern and central Wasatch Front
between 9pm and midnight, but given the weakening trends
expecting this to manifest as increased clouds with virga and a
few areas of gusty winds. In terms of gust magnitude, 12Z HREF
members have widespread likely 30+ mph gusts from the west desert
between I-80 and US-50 northeastward to the Wasatch Back, but only
20-30% of members showing pockets over 40 mph. Thinking the usual
windy and well-sampled west desert locations such as Dugway
Proving Ground has the best chance (about 40%) of seeing a gust
over 40 mph. These activity will wane overnight but continue to
track east of I-15 into the higher terrain.

A 500MB upper-level trough will begin to settle into the Northern
Rockies tomorrow, placing our area under increasing southwest flow
aloft just ahead of the trough axis. Tomorrow`s threat is
expected to be confined to areas generally east of I-15 and south
of I-80, with drier air aloft somewhat limiting activity given
similar instability profiles to today. Nevertheless, increased
flow will provide better shear, potentially allowing for
convection more capable of small hail. Meanwhile, dropping heights
and resulting cooling will put a cap on temperatures versus
today, dropping Sunday temperatures a few degrees for most
locations and 5-10 degrees from around Salt Lake County northward.
By Sunday night, the aforementioned trough will continue to dig
as it drops southward toward the Great Basin, pushing a mid-level
cold front across the CWA and setting up a southwest to northeast
oriented band of light precipitation, discussed further in the
extended discussion below.


.LONG TERM (After 12Z/6AM Monday)...At the start of the long-term
period, a positively tilted trough will be on our doorstep, with its
axis draped across western MT down across southern ID and
northwestern NV. At the surface however, its associated cold front
will be somewhat stationary across roughly from Cedar City up
through the Uinta Mtns. Convergence at the surface plus differential
heating across the boundary will strengthen the front before it is
finally pushed further east on Monday night. Models have trended a
bit more moist in the low levels, thus this moisture combined with
lift/instability along the boundary and daytime heating will yield
the highest chances for showers and thunderstorms mainly along said
boundary Monday afternoon. Aside from precipitation, expect breezy
westerly winds across far southern/southeast UT ahead of that
boundary.

On Tuesday, the cold core aloft will produce enough instability for
more showers and thunderstorms, primarily across northeastern
portions of the forecast area (i.e. Wasatch Front up to the Cache
Valley and across to the Uinta Mtns). Speaking of cold...snow levels
will drop with this system down to around 7000-8000ft, with the
Uinta Mtns receiving 4-8 inches in the highest elevations. Across
the area, highs will drop to 10 to 20 degrees below normal. Models
suggest the upper-level trough will phase with a closed low to our
south, likely bringing colder air further south than what we`ve seen
in previous model runs. Thus, even areas like St. George can expect
highs down to 10 degrees below normal.

Temperatures will rebound on Wednesday as a shallow shortwave ridge
crosses the area. Beyond Wednesday, uncertainty in the upper-level
pattern increases. Currently, 87% of ensemble members have some
degree of a trough moving through on Thursday and/or Friday. The
remaining 13% only favor a weak trough quickly passing through the
area. Across southern UT, where a trough passage is less likely,
only 30% of ensemble members have an appreciable decrease in
temperatures.


&&

.AVIATION...KSLC...Light northwest winds will prevail through around
03Z when winds transition to southeast. Scattered to broken clouds
will build in from the south by 03Z. Isolated to scattered showers
from 03-12Z will be capable of gusty, erratic outflow winds.
Prevailing southeast winds will transition to northwest around 15Z.

.Rest of Utah and Southwest Wyoming...As a weak boundary lifts into
northern Utah and southwest Wyoming, clouds will build with isolated
to scattered showers capable of gusty, erratic outflow winds.
Showers will reach KPVU around 02Z and KLGU around 05Z. Showers will
diminish around 12Z. Gusty southwest winds will diminish by 03Z
throughout southern Utah with clearing conditions. West to northwest
winds will prevail by 15Z for southwest Wyoming and northern Utah,
while southwest winds will prevail for southern Utah.


&&

.FIRE WEATHER...A boundary lifting northward this afternoon and
evening will bring scattered high-based virga showers and
isolated thunderstorms with a low-end potential of gusts up to 40
mph as far north as I-80. Wetting rains are highly unlikely with
these storms.

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. Wetting rain potential will be highest (around 70
percent) over the higher terrain in northern Utah from the
central/southern Wasatch northeastward to the Uintas, with snow
levels dropping near 8000 feet. A partial break in the weather is
possible on Wednesday, with the next storm system potentially
arriving during the latter half of the week. Elevated transport
winds and modest mixing will support good to excellent afternoon
clearing indicies each day. The unsettled conditions will also
bring elevated afternoon surface winds, particularly east of I-15
and south of US-6.


&&

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

$$

SHORT TERM...Van Cleave
LONG TERM...Cunningham
AVIATION...Wilson

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity