028
FXUS65 KSLC 132153
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
353 PM MDT Mon May 13 2024

.SYNOPSIS...A weak storm system will graze northern Utah through
this evening before another system moves through the area Tuesday
into Wednesday, bringing less warm and more unsettled conditions.
High pressure will return late in the week with a renewed warming
and drying trend.

&&

.SHORT TERM (Through 12Z/6AM Wednesday)...Early Monday afternoon,
a shortwave trough was rotating eastward through southwest Idaho.
Increased moisture, lift and kinematics associated with this
feature will move across northern Utah and SW Wyoming this
evening. The combination of 500-750J/kg of SBCAPE (per HREF
ensemble mean), deep-layer shear in the 25-30kt range, just
enough moisture (PWATs in the 0.5" to 0.6" range) and ascent from
the shortwave will be enough to encourage isolated to scattered
showers and storms, with a few stronger storms across northern
Utah and SW Wyoming through this evening. Main hazards will be
gusty microburst/outflow winds, lightning and sub-severe hail up
to 3/4" of an inch. Latest HREF wind probabilities peg a 70%
contour for gusts up to 39 mph across northern Utah, with a 10%
probability contour for gusts up to 58 mph centered over extreme
NW Utah. There is a region of higher wind probabilities over the
Dugway area as well, a region that is no stranger to
convectively-induced wind gusts. Farther south, isolated showers
are attempting to initiate over high terrain areas of southern
Utah, but with much lower lift, instability and shear here,
activity will tend to diminish as it moves off the terrain. Thanks
to the large-scale ascent courtesy of the shortwave, additional
shower and thunderstorm development will persist through the
evening across northern Utah and SW Wyoming, with activity
winding down quickly after midnight.

A weak cold front associated with this lead shortwave will stall
over central Utah tonight. A trailing shortwave will pivot across
eastern Idaho and northeastern Utah by Tuesday afternoon,
reinvigorating shower and thunderstorm activity. While convective
initiation can`t be ruled out across terrain features across the
area, initiation will tend to be tied to the near stationary
frontal boundary across central Utah. Moisture, lift, instability
and shear parameters look similar for tomorrow when compared to
day, with the most robust ingredients centered over central Utah.
Gusty outflow winds and sub-severe hail will be the main threats.
With weak westerly flow parallel to the nearly stationary frontal
boundary, there as a low-end risk for flash flooding should any
stronger cells tend to train across vulnerable locations. 1-hr
ensemble max QPF values do reach into the 0.50"-1.00" range,
suggestive that cells that verify on the high end of the
distribution could indeed present a low-end flash flood risk.

Finally, the HRRR smoke does indicate a low concentration of
near-surface smoke that is shown advecting across the area in the
post-frontal airmass across northern and central Utah on Tuesday.
This smoke appears to be originating from a wildfire in Oregon.
Check Utah DEQ for air quality forecasts.


.LONG TERM (After 12Z/6AM Wednesday)...Long term forecast period
begins within cooler deep north to northwesterly flow as a weak
grazing shortwave departs eastward. Some semblance of an associated
diffuse frontal boundary may remain draped across the south and
eastern portions of Utah, but expect this feature to largely be
washed out and only serve as maybe a very slight enhancement to
lower level convergence. In general, area will remain unsettled
enough to see some isolated to scattered afternoon convection fire
off of Utah`s high terrain (as well as likely SW Wyoming) and
subsequently gradually drift south to southeastward downwind.
Subcloud layers will be fairly dry, so could see some moderate
downburst winds from any convection that matures sufficiently.
Additionally, given fairly weak storm motion, could at least see
some potential for convection to drift over more sensitive and fast
responding drainages/washes, and will need to keep an eye on flood
threat accordingly. That said, given dry subcloud layers (though
PWATs near normal) and limited coverage, thinking the threat overall
is on the lower end. Aside from the precipitation potential, weak
post frontal environment will result in slightly cooler afternoon
temperatures than the prior day, though still near to slightly above
normal. Additionally, HRRR Near-Surface Smoke Density product
suggests maybe some lingering light smoke/haze associated with the
ongoing Little Yamsay fire in Oregon, though that will also be
dependent on ongoing containment efforts.

Guidance for Thursday still shows good agreement in ridging nosing
in from the west, with continued ridging into Friday now also
supported by the majority of deterministic and ensemble sources. In
addition to increased dry and stable conditions, this ridge will
help initiate a warmup, with forecast highs along the Wasatch Front
by Friday in the low to mid 80s, and for Lower Washington County in
the mid 90s. While highly unlikely, NBM probabilities do show a 4%
chance of KSLC hitting 90F for the first time this year. For those
not ready to hear it, the good news at least is that the average
first date of 90F or higher for KSLC is not until June 8th, so we
probably have a little more time to enjoy Spring.

Unfortunately, suite of ensemble guidance continues to diverge on
the pattern evolution moving into the weekend, primarily in regard
to the position/strength of the ridge as a modestly strong mid/upper
jet and impulse approaches through the PacNW. An additional muddying
factor is a more southern stream cutoff low approaching the
mid/lower California coast, and if/how/when this may interact with
the northern stream. A stronger ridge solution would yield continued
warm/dry conditions, where a trough would bring about cooler and
more unsettled conditions depending on the strength. For Saturday,
ensembles sit with roughly 55% of members supporting continued
ridging, and 45% supporting at least some sort of weak troughing.
Sunday stands closer to a 50%/50% split between trough/ridge, with
20% of overall solutions showing some phasing between southern
cutoff and northern trough, which would be the coolest/wettest of
plausible solutions. Monday offers little in the way of extra
confidence. Opted to keep NBM values with this forecast package,
which include isolated to scattered showers/thunderstorms and
seasonably mild conditions, but worth mentioning the spread between
25th/75th percentile for highs remains around 10F or so. Overall,
will likely see exact numbers for temps/PoPs fluctuate a decent bit
until guidance hopefully begins to trend towards a solution.


&&

.AVIATION...KSLC...Showers and thunderstorms, mainly to the
northwest, will diminish by around 06Z. Sprinkles or light rain
showers are likely, but outflow winds from 00-03Z could enhance
prevailing northwest winds. Clouds will diminish as showers and
thunderstorms taper off. Winds will transition to southeast around
06Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms for southwest Wyoming and northern Utah will diminish
by around 06Z. Gusty, erratic outflow winds are likely near showers
and thunderstorms. Those will diminish from 03-06Z. Showers will be
isolated further south with less outflow wind compared to the north.
Showers will diminish through the evening.

&&

.FIRE WEATHER...A weak cold front will move through northern Utah
this evening, bringing isolated showers and thunderstorms. The
weak cold front will move southward across central Utah on
Tuesday, and finally to southern Utah by Wednesday. Isolated
to scattered showers and storms will accompany the front each day,
favoring central and southern Utah by Tuesday and Wednesday.
Isolated areas will see wetting rains, but most areas are not
expected to see wetting rains with this activity. Warmer, drier
conditions will build across the state for Thursday and Friday,
with increasingly poor overnight recovery across southern Utah,
especially for lower elevation areas. Another weak system is
forecast to graze northern Utah this weekend, bringing some gusty
westerly winds, especially as one approaches the Idaho border.

&&

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

$$

ADeSmet/Warthen/Wilson

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