Severe Thunderstorm Warning 34, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
316 PM MDT Wed Jul 24 2024

.SYNOPSIS...High pressure over the Great Basin will move overhead
today, resulting in near record warmth for northern Utah. Moisture
will spread northward across the entire state by Thursday,
resulting in the threat of showers and storms areawide. Drier air
will move in for the weekend with increasing winds.

&&

.SHORT TERM (Through 12z Friday)...Afternoon satellite and H5
analysis place the core of the upper level High pressure near the
triple point of UT/NV/AZ attm...latest trends showing a slight
eastward jog to the east over the last several hours. Positioned
within the northeastern periphery of this is a remnant MCV (with
subtle circulation coincident) providing just enough additional
forcing to be a focus of convective initiation this afternoon, and
will continue to be as it lifts northeastward through
tonight/early tomorrow morning.

A skosh more instability exists across the southwestern portions
of the area this afternoon vs. 24 hours ago, largely due to the
eastward shift of the high and further deepening of PWAT near the
UT/NV border. Will have to continue to monitor localized flash
flooding threats, including recent burn scars, through this
evening as the stronger cores of late have produced observed
rainfall rates as high as .50"/20 min (STP ~1"/hr) indicating the
efficiency of the environment. Future coverage in the near term is
expected to continue to expand across the southwest and UT/NV
border region, though extent should remain scattered in nature and
focused over the terrain.

The aforementioned remnant MCV will gradually shift into west-
central Utah tonight, then northern Utah Thursday morning
maintaining some nocturnal shower potential, and potentially
isolated nocturnal convection...exiting the region around midday.
In wake of this wave noting a high likelihood for substantial
suppression across central/northern Utah through much of the
afternoon hours, even with a primed/juiced airmass in excess of 1"
PWAT. CAMs do break capping leading into the evening hours in
advance of a short wave poised to translate in from the west and
are keying in on a more organized convection tracking W-E across
much of the area late evening/overnight. Noting 90% threshold
probs for winds in the 40-50mph range across the western deserts
within the 00z-06z Friday window...will have to continue to
monitor later runs for consistency. Additionally, given the
airmass, will have to monitor heavy rain potential as well.

.LONG TERM (After 12z Friday), Issued 351 AM MDT... Friday and
Saturday will be the coolest days of the week throughout southwest
Wyoming and Utah. After powerful ridging tracks to the east and a
trough tracks far to the north, temperatures will cool to near
normal. Positioned between those systems, the pressure gradient
will strengthen locally, allowing for enhanced southwest winds.
Wind gusts Friday will be around 25 mph in southwest Utah and
southwest Wyoming. Relative humidity in the afternoon when winds
peak will be from roughly 15- 25%, enhancing fire danger.
Scattered afternoon showers and thunderstorms are likely. As drier
conditions build in with drier southwest flow, showers and
thunderstorms will taper off by around 6 p.m. throughout southern
Utah. Showers and thunderstorms will last further into the evening
throughout southwest Wyoming and northern Utah. Gusty, erratic
outflow winds and locally heavy rainfall are likely.

The trough will lift into Canada Saturday, and a broad longwave
trough will build into the western U.S. With ridging positioned to
the southeast, more enhanced southwest flow is forecast. Wind gusts
will be slightly higher than Friday, around 30 mph. Minimum relative
humidity will be slightly lower.

Drier southwest flow will build in Sunday, with a dry day likely
throughout southwest Wyoming and Utah. As ridging to the southeast
retrogrades, winds will be lighter, but gusts around 25 mph are
likely.

There is good agreement that moisture will build through the week
into Utah. Through the start of the week, that will largely be high-
based showers and thunderstorms for much of southern Utah capable of
gusty, erratic outflow winds.

&&

.AVIATION...KSLC...VFR conditions are expected to prevail through
tonight with mid and high based cloud cover forecast. Isolated
thunderstorms are possible this evening with gusty outflow winds
potentially impacting the terminal. Northwest winds will shift out
of the southeast at 04z at light speeds. Tomorrow morning, look for
light rain showers to potentially drop visibilities at the terminal
with a mid level cloud deck. There is around a 10 percent risk for
thunder associated with these showers tomorrow morning.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered thunderstorms will
once again dominate southern Utah but also spread across western
Utah through this evening. These thunderstorms will be capable of
producing gusty outflow winds, heavy rains, lightning and reduced
visibility at area terminals. Otherwise, VFR conditions will prevail
in central UT and SW WY tonight. Tomorrow morning, look for light
rain showers to potentially drop visibilities across western and
northern UT terminals. Gusty outflow winds may also accompany these
showers with around a 10 percent risk for thunder.

&&

.FIRE WEATHER...Scattered shower and storm development has once again
formed over the southwestern portions of the district this
afternoon, with spotty wetting rains within brief heavy rain
focused over the higher terrain of FWZ 493/496 and portions of
495. Areal coverage of showers/storms (and attendant spotty
wetting rains) will expand north and east beginning tonight as a
weak wave currently over the Nevada lifts through the region.
Areawide shower and storm development is expected Thursday into
the overnight hours as the high pressure in place shifts east
whilst weakening, allowing a trailing disturbance to provide more
storm organization Thursday afternoon/evening. Noting increasing
RH trends over the next 36 hours as such.

Thereafter, a slot of significantly drier air and increasing
southwesterly flow will begin to spread into southwestern Utah
Friday, while the north will remain in a more moist environment
capable of additional p.m. showers/storms Friday. Increasing
southwesterly winds and further drying will bring the potential of
critical fire conditions once again beginning Saturday.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Heat Advisory until 10 PM MDT this evening for UTZ101>107-116.

WY...None.
&&

Merrill/NDeSmet/Wilson

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

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