602
FXUS65 KSLC 252220
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
420 PM MDT Tue Jun 25 2024

.SYNOPSIS...Showers and thunderstorms will spread across the
state on Wednesday with a gusty wind threat across northern Utah
and isolated flash flood risk across southern Utah. Another round
of strong thunderstorms is expected Thursday afternoon and
evening. After briefly cooler temperatures Friday, hot and dry
weather returns across the state this weekend.

&&

.SHORT TERM (Through 12Z Thursday)...Moisture remains in place
across southern Utah this afternoon, with a PW gradient from
around 1 inch near the AZ border dropping off to less than 0.7
inches north of I-70. Combined with daytime heating, CAPE values
around 500-1000 J/kg of CAPE, this environment is support diurnal
convective development across southern Utah. Light westerly flow
is favoring downstream convective development on a cold pool
across the eastern Grand Staircase moving toward Lake Powell. This
is where the highest Flash Flood potential will continue in the
near term.

Tonight, an shortwave moving northward through AZ around the
western periphery of the SW high pressure, will track into
southern Utah, and will interact with weak surface boundary and
moisture gradient over southwestern Utah. This will increase the
potential for showers and thunderstorms over St George, Zion,
Cedar City and north to Beaver tonight. In particular, there is an
increased potential for training and redevelop along the stalled
boundary over southwest Utah overnight tonight, which is when the
isolated flash flood potential will peak for the aforementioned
areas. As this wave continues to work northward overnight and
interacts with the increasingly dry airmass into central Utah, the
convective hazard will transition from Flash Flooding to more of
a gusty outflow wind potential. This will also increase southerly
winds and cloud cover all the way into central and northern Utah
by early Wednesday morning. This will help to limit cooling
overnight tonight, allowing for one more warm night, with minimal
overnight relief from the daytime heat.

On Wednesday, the aforementioned shortwave will be ejecting
northeastward into WY/CO leaving Utah under subsidence behind the
wave. This will help to allow for breaks in the cloud cover and
increase diurnal heating through Wednesday morning, with more
widespread moisture in place across the state of Utah. By
Wednesday afternoon, another weak wave in the west-southwesterly
flow will increase ascent and aid in convective initiation.
Showers and thunderstorms will become more widespread on
Wednesday, especially south of I-80 and through central Utah.
Across the northern half of the state, the primary hazard will be
gusty outflow winds, with perhaps a few isolated severe wind
gusts. Otherwise, for southern Utah, deeper moisture in place will
act to limit the wind potential, instead favoring another day of
an elevated Flash Flood potential, mainly for portions of the
Grand Staircase, Glen Canyon, Capitol Reef and the San Rafael
Swell.

.LONG TERM (After 12Z Thursday), Issued 428 AM MDT...
A progressive pattern will develop for the long term period as
the ridge of high pressure responsible for the recent heat will
shift east into the southern CONUS. Ample moisture will only be in
place on Thursday as the first trough pushes through to our
north. A dry airmass will be ushered in behind the aforementioned
trough. This airmass will help to cool temperatures briefly, but
the dry conditions will persist through the remainder of the
period. This dry airmass will pair with windy conditions as
another trough moves into the region this weekend resulting in
favorable fire weather conditions.

The approaching trough on Thursday will pair with PWATs (~1.2"
for KSLC) approaching climatological maxes for this time of year.
Forecasted CAPE values near 1000 J/kg and bulk shear >50kts will
create an atmosphere conducive for strong to severe thunderstorms
across the CWA. The limiting factor, however, will be how much
precipitation and cloud cover will be lingering across the region
from the previous days convective activity. A lot of the hi-res
guidance does keep precipitation ongoing Wednesday night into the
morning on Thursday. If these showers are able to dissipate early
enough then the atmosphere could become primed for strong
thunderstorm development as the axis of the trough passes through
Utah and SW Wyoming. In addition to the threat of severe weather,
flash flooding will also be a concern across flood prone regions
such as dry washes, slot canyons and burn scars.

This precipitation will quickly shift east and out of the CWA
late on Thursday as drier and cooler air advects in behind the
frontal passage. Friday`s high temperatures will be the coolest of
the long term period with near normal temperatures. Shortwave
ridging will temporarily build back into the area on Saturday
leading to high temperatures returning to ~5 degrees above normal.
Similar temperatures on Sunday along with increasing
southwesterly flow ahead of our next trough will lead to gusty
winds developing across most of the CWA. The dry airmass will be
characterized by minimum relative humidity values <15% for the
afternoon on Sunday. The trough axis will push east of us on
Monday with temperatures the remainder of the period returning to
near normal and winds weakening slightly, but staying elevated.

&&

.AVIATION...KSLC...Northerly winds remain in place over the KSLC
terminal through the daylight hours, reverting back to a southerly
flow around 04Z. Mid-level cloud cover will increase through the
overnight hours with CIGs remaining around 12kft AGL. Vicinity
shower activity will increase through the morning hours tomorrow,
and may bring gusty and erratic winds after 12-13Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Widely scattered showers and
thunderstorms will continue through the remainder of the day across
southern Utah, bringing areas of heavy rainfall as well as gusty and
erratic outflow winds. Showers will continue into the overnight
hours across the western half of Utah, spreading northward by the
early morning hours. A similar threat of gusty and erratic outflow
winds will exist through this period over western Utah. Otherwise,
winds will continue to follow diurnally driven trends outside of
local showers and thunderstorms while maintaining VFR conditions and
CIGs around 10kft or above.

&&

.FIRE WEATHER...
Moisture remains in place across southern Utah this afternoon
supporting continued isolated to widely scattered shower and
thunderstorms this afternoon, with an isolated flash flood threat.
This evening a wave will move northward out of Arizona and
brining additional moisture northward across the state of Utah for
Wednesday. Locally heavy rain is possible this evening over
southwest Utah as this moves northward, transitioning to a gusty
outflow wind potential across west-central Utah tonight as this
continues moving northward.

On Wednesday, the more widespread moisture will result in higher
afternoon humidity values as well as a more widespread shower and
thunderstorm potential. A few storms could be strong with isolated
small hail, and gusty outflow winds, particularly across central
Utah, and perhaps portions of northern Utah. Across southern Utah,
the storms will be more capable of locally heavy rainfall and
isolated flash flooding.

Thursday, a trough moving in from the northwest will introduce a
drying trend from west to east, which will favor showers and
thunderstorms over eastern Utah with lowering humidity values
across western Utah.

By Friday into through the weekend, another Pacific trough will
move in to our northwest which will continue to support a west-
southwesterly flow of drier air moving into the area. The potential
for critical fire weather conditions (low RH and winds) will start
across southwest Utah on Friday, expand across more of western
Utah on Saturday, more statewide by Sunday, then shift to the
southeastern portion of the state by Monday as a weak cold front
moves into northern Utah.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Excessive Heat Warning until 11 PM MDT this evening for UTZ101-
     104>106-116.

     Heat Advisory until 11 PM MDT this evening for UTZ102-103-107-
     118-119.

WY...None.
&&

$$

SHORT TERM...Church
LONG TERM...Mahan
AVIATION...Webber
FIRE WEATHER...Church

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