Area Forecast Discussion Issued by NWS Salt Lake City, UT
000
FXUS65 KSLC 191017
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
417 AM MDT Tue Mar 19 2024
.SYNOPSIS...High pressure will continue to build into northern Utah
maintaining warm, dry, and stable conditions through the week.
Meanwhile, a closed low over Arizona will persist will minimal
impacts to southern Utah into Tuesday. Confidence is increasing
that a strong cold front will move through the region in the late
Saturday through Sunday timeframe, bringing a return to widespread
unsettled conditions.
&&
.SHORT TERM (Through 12Z/6AM Friday)...Early Tuesday morning
analysis continued to show the presence of a Rex Block across the
western CONUS, with a high pressure ridge centered over Northern
California, while a closed low remained stationary over west-
central Arizona. This stubborn low has now been in place in this
same general vicinity going back all the way to last Thursday
morning! "Low" and behold, model consensus indicates that this
low will finally get on the move, with last round of guidance
showing the low opening up into a trough this evening before
migrating eastward towards the Four Corners. The future of the
strong ridge is ill-fated as well, as it is forecast to weaken and
translate overhead by late Wednesday. Dry, stable and steadily
warming conditions will be in place across most of the area
through Wednesday as a result, when high temperatures will rise to
5F to 15F above seasonal normals. An exception will be across
southern Utah, particularly near the Arizona border, where
isolated showers and perhaps a thunderstorm or two will develop
this afternoon as these areas will reside near the northern
periphery of best moisture. Notably, the QPF forecast has dropped
off considerably when compared to the forecast 24 hours ago when a
couple of areas of 0.30-0.40" of QPF were noted on ensemble max
plots. Now, those values have dropped down to around 0.10"; and
centered mainly over high terrain convection initiation sources.
A weak shortwave trough is forecast to translate eastward across
northern Utah and SW Wyoming Thursday afternoon. Just enough
moisture is forecast to be in place to allow for the development
of a few showers across northern/central Utah and SW Wyoming
during the afternoon and early evening. With 150-300J/kg of SBCAPE
forecast to be in place, an isolated thunderstorm cannot be ruled
out, with the most favored corridor across central Utah.
.LONG TERM (After 12Z/6AM Friday)...A ridge at the start of the long-
term period will be short-lived as a broad trough pushes into the
western US, bringing active weather to the forecast area through at
least Tuesday.
Friday and Saturday morning will feature the first portion of the
storm system, comprised of above-normal temperatures and increasing
southwesterly flow as the ridge axis shifts eastward. As moisture
filters into northern Utah on Friday, showers are likely to develop
during the afternoon, especially across higher terrain, taking
advantage of decent instability and southwesterly-favored orographic
enhancement. Light precipitation may continue through the overnight
and morning hours, though synoptic lift will be very limited until
Saturday morning. A few thunderstorms aren`t out of the question for
Saturday afternoon ahead of the front, with fairly steep lapse rates
and increasing moisture, though cloud cover may limit solar heating
and thus convective development. As for increasing southwesterly
winds, anticipate winds to be highest across western and especially
southern Utah. The NBM 50th percentile wind gusts currently peak at
around 45 mph in southwestern valleys, so this is a detail to keep
an eye on regarding any future headlines. Regarding precipitation
type, in this first phase, given warm antecedent conditions, valleys
will remain as rain, with snow levels peaking at around 8000 ft
Friday afternoon.
The heaviest precipitation will likely occur along the frontal
passage, especially for valley locations. While the exact timing
remains a bit fuzzy, the cold front should reach northern Utah
roughly between Saturday afternoon and Saturday night. There is now
higher confidence in a strong drop in temperatures and snow levels
with the front, whereas yesterday was favoring a more gradual
decrease. Along with mesoscale forcing along the baroclinic zone,
Utah will be located in the polar exit region of a 170kt jet, thus
promoting plentiful upper-level lift. Moisture will stick around
behind the frontal passage, likely lasting through at least
Tuesday...thus precipitation chances continue. In the mountains, a
prolonged period of northwesterly flow will be good for favored
areas such as the Upper Cottonwoods or in the Tushar Mountains.
Beyond Sunday, ensemble members start to diverge quite a bit with
the upper-level pattern, mainly with the progression of the main
trough.
Looking closer into valley precipitation type along/behind the cold
front, most valleys below 5000 ft will remain as rain, though there
is always the chance for further lowering of snow levels with
heavier precipitation. Keeping in mind plenty of uncertainty,
additional colder air filtering in early in the work week could
produce snowfall early Monday or Tuesday morning(s).
&&
.AVIATION...KSLC...Light, diurnally-driven winds will continue with
VFR conditions. A transition to northwesterly is expected around 19-
20z.
.REST OF UTAH AND SOUTHWEST WYOMING...Light, diurnally-driven winds
will continue with VFR conditions. There is a very low (10%) chance
of a few isolated showers developing this afternoon across
southwestern Utah, though these are unlikely to be impactful.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
ADeSmet/Cunningham
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