154
FXUS65 KSLC 210958
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
358 AM MDT Sat Sep 21 2024

.SYNOPSIS...Low pressure crossing the Desert Southwest will bring
showers and thunderstorms Saturday, primarily to southern and
eastern Utah. A mostly dry front will cross northern portions of
the area on Monday before high pressure moves in for much of the
remainder of the upcoming week.

&&

.SHORT TERM (Through 12Z/6AM Monday)...Recent satellite imagery
reveals a closed low located over the CA/AZ border early this
morning, with the overall longwave trough becoming more neutrally
tilted. Thus, we can expect this low to begin to lift northward
this morning, reaching the Four Corners area by this afternoon.
Given enough mid-level lift and sufficient moisture, showers have
lingered through the overnight hours across southwestern Utah,
with more light showers just starting to move northwards over Lake
Powell. As this low progresses, showers will become more
widespread, particularly over southeastern Utah. Chances for
thunder will increase this afternoon with daytime instability,
with thunderstorms reaching as far north as the Uinta Mtns. Gusty
microburst winds will be the main threat, though a flash flood
risk exists given ensemble max QPF reaching 0.25-0.75" over the
southern mountains.

Easterly canyon winds overnight have been very localized, only
gusting at canyon mouths. The highest gusts so far have been near
Weber Canyon, gusting to 45 mph. Easterly canyon winds are likely
to return late Saturday night, though will likely remain below
advisory criteria. The 00z HREF was a bit more excited, with an
ensemble max of 30-40 mph along the northern Wasatch Front, though
recent runs of the HRRR have backed off.

As the low exits eastward, a shortwave ridge will bring high
pressure to the area for Sunday. Dry conditions and near-normal
temperatures are expected...perhaps a great day for leaf-
peeping.

.LONG TERM (After 12Z/6AM Monday)...Deterministic global and
ensemble system agreement has improved through midweek, with
consensus favoring broad northerly flow through Wednesday, with Utah
and SW Wyoming residing on the eastern periphery of a building PacNW
ridge. Enough lingering moisture and cyclonic flow remains to
support an isolated shower across southern Utah Monday and Tuesday
afternoon/early evening, but this activity will be few and far
between. Such a pattern also allows for largely seasonable to
slightly above normal temperatures into midweek. Heading into the
second half of the workweek, upstream PacNW ridge is shown cresting
across the Great Basin, ensuring dry, stable and outstanding early
Autumn weather with high temperatures ranging 5F to 15F above
normal. As we head into the later portion of the week and into next
weekend, there is some uncertainty introduced regarding the strength
and timing of shortwaves progressing through the southwestern
Canadian provinces and International Border region. Solutions range
from keeping the ridge firmly in place to those with stronger
grazing troughs that may offer a slight cooldown along with locally
breezy conditions. Even members with the strongest troughs offer
little in the way of precipitation as we head into next weekend,
with only ~10% of the solution space offering light precipitation
amounts by next weekend.

&&

.AVIATION...KSLC...VFR conditions will persist for the KSLC terminal
through the period. Afternoon cumulus buildups are likely on nearby
terrain this afternoon, especially east of SLC. There is a very low,
or less than a 15% chance for an afternoon/early evening shower.
Winds will largely be variable through 16Z, with guidance pointing
towards a general WNW consensus until then, if we had to choose a
direction. Gusty NNW winds expected by 20Z, with gusts to around
20kts. Sfc winds expected to turn to the SSE between 03-04Z. Some
volatility in direction likely after 03Z Sunday due to the presence
of easterly canyon winds near the terrain.

.REST OF UTAH AND SOUTHWEST WYOMING...An area of low pressure will
move through southern Utah into Saturday evening, providing showers
and thunderstorms, especially along/east of the spine of the
mountains, with coverage increasing as one approaches the CO and AZ
borders. Largely VFR conditions expected, however can`t rule out
brief mountain obscuration in briefly heavier convection, along with
gusty and erratic winds. Canyon winds expected to develop along the
lee of the Wasatch and the Sessions after 06Z Sunday, with local
gusts near 30kts through mid-morning Sunday.

&&

.FIRE WEATHER...A low pressure system currently located on the CA/AZ
border will continue to make its way eastward, lifting northward
across CO late Saturday and into Sunday. Showers and thunderstorms
will increase in coverage further eastward through Lake Powell
through the morning, then northward through the Uinta Mtns by the
afternoon with the progression of that low. Gusty and erratic
winds may accompany these thunderstorms, as well as an increased
chance for wetting rains, particularly across southeastern UT.
Precipitation chances will end by late Saturday night as high
pressure begins to push into region, though expect improving
overnight RH recoveries through Sunday night. A mostly dry cold
front will push through northern/central UT on Monday, with only a
chance for isolated showers over eastern UT. Critical fire weather
conditions are not expected with this front. Afterwards, stronger
high pressure is likely to build, producing a gradual drying
trend through the week.

&&

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

$$

Cunningham/ADeSmet

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