654
FXUS65 KSLC 112159
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
359 PM MDT Sat May 11 2024

.SYNOPSIS...Low pressure east the region Sunday will result in
another day of mainly high terrain showers and thunderstorms,
though high temperatures will warm to near seasonal normals. While
a few showers will linger through Tuesday, conditions will become
less unsettled by the second half of the week along with steadily
warming temperatures.

&&

.SHORT TERM (Through 12Z/6AM Monday)...Early Saturday afternoon,
an area of low pressure was located over extreme southeast Utah.
Cyclonic flow around the low was combining with daytime heating
and modest moisture (PWATs between 0.4"-0.5") to produce a
smattering of showers and thunderstorms, primarily along/east of
Utah`s mountain spine, with activity is moving off to the south
and west. With minimal instability (SBCAPE values up to 500J/kg)
and little/no deep-layer shear, convection is lacking
organization with rainfall rates limited to the light to moderate
category. Most cells have contained instantaneous rates of up to
0.20"/hr. Thus the main hazards with this activity will be
lightning and gusty outflow winds (thanks to dry sub-cloud
layers) with any convection as it decays after moving off of
terrain. We can`t completely rule out an isolated flash flood
risk, however -- but this hazard should be limited to vulnerable
locations where any convection is able to train, or repeatedly
move over the same location.

Convective activity will gradually wane with the loss of daytime
heating this evening. As we head into Mother`s Day, model
consensus is in good agreement in indicating that the low will
propagate eastward across Colorado. Just enough moisture and
lingering cyclonic flow appears to remain in place to promote
isolated showers and storms off of terrain once again, with
coverage being more limited when compared to the past couple of
days. Main hazards will once again be lightning and gusty outflow
winds. Temperatures will continue to warm a couple of degrees as
we close out the weekend.

.LONG TERM (After 12Z/6AM Monday)...Long term forecast begins
with a weak ridge being flattened by a weak grazing northern
stream shortwave. Despite the grazing wave, mild H7 temperatures
around 7C to 10C will remain in place Monday, with corresponding
afternoon high temps running about 5F to 10F above climatological
normal. That said, the weak wave will add just enough energy in
combination with diurnal heating to trigger some isolated to
scattered showers across northern Utah as well as portions of
Utah`s high terrain.

On Tuesday, guidance shows fair agreement in a slightly stronger
(but still largely unremarkable) impulse following on the heels of
Monday`s weak shortwave. There remains some spread in the exact
strength, but generally anticipate a bit more widespread scattered
convection Tuesday, maximized with peak daytime heating, and still
favored over the high terrain and downwind adjacent valleys. In
terms of QPF, 90th percentile amounts only peak at around 0.10" to
0.15" or so for high terrain, with lesser amounts in those adjacent
valleys. Given some convective nature to the showers though, would
expect measurable precip to be a bit scattershot overall. Less
agreement is noted in strength/timing of an associated cold frontal
boundary, but general consensus is something of a loose front
sinking southward into the region Tuesday. Expect this to knock
temperatures across the northern half of the forecast region
downward by about 5 degrees or so, and also potentially serve as a
bit of an enhanced focus for precipitation depending on how well
defined it is.

By midweek, ensembles lean in favor of a combination of a weak
southern stream cutoff low and Tuesday`s departing impulse to help
keep the forecast region in a cooler deep northerly flow regime.
This will help temperatures cool a bit more back to near
climatological normal, and allow for some isolated diurnal
convection, once again largely favored over the high terrain of the
area.

Thereafter, solution space begins to widen in regard to flow
evolution of the area, and thus certainty in exact forecast details
dips. Clusters seem somewhat split on if stronger ridging can nose
back into the region (more mild and dry conditions / ~50% of
ensemble members), if a more zonal flow type pattern develops (more
muted warmup and likely modestly unsettled over high terrain / ~40%
of ensemble members), or if a quicker and stronger trough can begin
to dig in (cooler and more unsettled / ~10% of ensemble members).
ECM members seem to be weighted more towards the zonal flow or
trough solutions, where GFS/Canadian members show a bit more lean
towards ridge solutions (though a bit more well dispersed overall).
Current forecast carries seasonably mild and largely dry conditions,
but as is often the case, will want to keep an eye on trends in the
coming days to see how things eventually wind up.

&&

.AVIATION...KSLC...Isolated mountain showers have a 15% chance of
producing gusty outflow winds up to 25kts that reach KSLC before
02z. Winds will likely transition to light and southeasterly around
02-03z, but may occur as early as 01z. VFR conditions will prevail.

.REST OF UTAH AND SOUTHWEST WYOMING...Isolated to scattered showers
will continue through roughly 03-05z south of roughly KENV-KSLC-
KEVW. Many of these showers will be capable of producing gusty and
erratic outflow winds and lightning. Additionally, showers may
struggle to move off of higher terrain, especially further north.
Within the heaviest showers, MVFR conditions are possible.

&&

.FIRE WEATHER...An area of low pressure will be in place over
Colorado on Sunday, promoting the development of isolated
afternoon and early evening showers and thunderstorms, mainly over
high terrain areas and adjacent valleys. A weaker system will
graze northern Utah on Monday, bringing an isolated
shower/thunderstorm or two to northern Utah, especially over
terrain. This trough will dig across eastern Utah on Tuesday,
bringing isolated to scattered showers and thunderstorms,
especially along/east of the I-15 corridor. Trends then favor at
least brief high pressure ridging by late in the week, and this
will favor a warming and drying trend. Somewhat unsettled
conditions may try and return next weekend.

&&

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

$$

ADeSmet/Warthen/Cunningham

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