Severe Thunderstorm Warning 26, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
103 PM MDT Sun Jun 11 2023

.SYNOPSIS...Strong thunderstorms is expected is across portions of
northern and central Utah this afternoon and evening. As the
upper level low gradually weakens Monday, expect another round of
showers and thunderstorms across much of the region during the
afternoon and evening.

&&

.SHORT TERM (Through 12Z Tuesday)...Ongoing convection event will
keep this forecast discussion relatively brief. Afternoon upper
air and satellite analysis indicates an upper level low lifting
across the southwestern United States with broad upper level
diffluence over Utah. As of 1 PM, mesoanalysis SBCAPE is near
1000-1500 J/kg across much of Utah and Uinta County, WY. Deep
layer shear near 30 to 40 kts has reached central Utah and
continues to progress northward associated with a 500mb speed max.

Convective initiation is ongoing as of 1 PM and is expected to
continue to rapidly develop across central Utah. Latest CAMS
suggest an increasing threat of strong wind gusts near to above 60
mph with the strongest storms as well as small hail. Current
forecast timing of the highest severe weather threat is as
follows:

Utah County by around 1 to 3 PM,
Salt Lake County 2 to 5 PM,
Davis/Weber 3 to 6 PM,
Cache/Eastern Box Elder 4 to 7 PM,
and Tooele City, Tooele County and Wendover (and the I-80
corridor between Wendover to Tooele) 3 PM to 6 PM.

Convective coverage will decrease overnight though not completely
end as several weak shortwave troughs embedded in the flow around
the upper level low will rotate through the area.

With continued weakening of the upper level low, storm motions
will decrease Monday afternoon and evening. This will bring the
threat of slow moving, but weaker showers and thunderstorms and an
attendant threat of isolated flash flooding.

.LONG TERM (After 12Z Tuesday)...Tuesday and Wednesday look to
offer a relative continuation of the ongoing pattern. The forecast
region looks to be placed within broad troughing which envelops
much of the W CONUS, and is characterized by embedded weaker
cyclonic impulses along with reinforcing shortwaves. Deep moisture
also remains favorable through this period, with ensemble mean
PWATs running roughly around 150% to 200% of climatological
normal. As a result, high precipitation chances remain. In
general, expect coverage to be maximized throughout the northern
half of Utah as well as southwestern Wyoming, particularly along
higher terrain and during peak diurnal heating. With relatively
weak steering flow and associated storm motions, precip will have
the potential to create hazardous conditions in rain sensitive
locations such as slickrock areas, burn scars, normally dry
washes, and slot canyons. Ensemble mean instability will be fairly
meager (~200-400 J/kg), as will shear, so stronger more robust
updrafts will likely be fairly isolated overall. Activity will
wane with loss of daytime heating, but synoptic forcing will be
sufficient to yield continued precipitation chances overnight,
albeit with less coverage.

For the latter half of the work week, the pattern shifts somewhat
and allows a slight drying trend with PWATs returning closer to
near to just above climatological normal levels. Region looks to
see flow generally zonal to southwesterly, with a shortwave trough
noted to the north, and a cutoff to near cutoff shortwave near
the lower California coast. The combination of more limited
moisture along with weaker synoptic forcing will bring daily
precip chances down in comparison to the prior days, with the
timing still favored during peak heating from the afternoon into
the early evening hours. Additionally, will begin to see
increasing 700mb temps, and an associated warming trend in
expected afternoon highs.

Moving into the weekend, guidance begins to diverge somewhat in
regards to handling the evolution of both the cutoff California
shortwave and the broader troughing extending southward from the
PacNW and Canada. A scenario similar to the deterministic GFS
where the cutoff shortwave opens and lifts through followed by a
deeper northern trough (and associated baroclinic zone) pushing
into the region would bring a quicker return to more active
weather. On the other hand, a more slowly ejecting California
trough and slower more glancing blow from the northern stream
trough would keep things a bit more steady state through the
weekend. Given the the spread in guidance, increased uncertainty
is noted through this period.

&&

.AVIATION...KSLC...Through ~20Z, minimal operational concerns are
forecast for the KSLC terminal. Wind will remain light out of a
northerly direction with mid and upper level cloud cover. After
~20Z, strong thunderstorms forming to the south of the terminal
will begin to encroach the airfield, with storm outflows shifting
winds to a southerly direction. There is a 60% chance that strong
thunderstorms impact the airfield between 21-23Z, bringing wind
gusts in excess of 30kts, CIGs as low as 5kft AGL, and VIS as low
as 3-5SM in heavy rain. Storms will progress past the airfield
after 23Z, with outflows from the north expected in the wake of
the storms.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered to widespread
showers and thunderstorms are expected across the northern half of
the region today, bringing gusty and erratic outflow winds, brief
heavy rain, and frequent lightning. Stronger storms will begin
forming around 18-19Z, progressing through the Wasatch Front, West
Desert, and Southwest Wyoming through 23-00Z, then into far
northern Utah through 01Z. CIGs will remain above 5-6kft AGL,
though heavy rain may bring VIS down to the 3-5SM range. For
central Utah, isolated showers will be possible, bringing similar
risks of gusty outflow winds, though coverage will be much less.
Additionally, central and southern Utah will experience
predominantly south to southwesterly flow with afternoon gusts in
excess of 20mph.

&&

.FIRE WEATHER...A gradually weakening upper level low will bring
the threat of strong convection today. With continued weakening,
storm motions will decrease Monday afternoon and evening,
transitioning to more of a heavy rain threat. As this first
remnant circulation lifts out of the area Tuesday, another upper
level low will shift east into the Desert Southwest. This will
keep unsettled conditions across the region, particularly across
northern and central Utah through the next 5 to 7 days.

&&

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

Kruse/Warthen/Webber

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

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