Severe Thunderstorm Warning 15, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
411 PM MDT Wed May 31 2023

.SYNOPSIS...Unsettled weather will increase in coverage and
intensity through the end of the week as an upper level low moves
in overhead and total column water increases to near an inch over
parts of the forecast area. The pattern remains progressive and
moist through the long term with temperatures hovering around
climatological normals.

&&

.SHORT TERM (Through 12Z/6AM Saturday)...The arrival of an upper
level trough moving eastward in from southern California will
usher in at least a few more days of unsettled weather. In a
pattern much more familiar to the monsoon season of late summer
than late May, moisture will continue to spread in overhead,
slowly filling in at the low levels, pushing PWATs up towards 0.75in
across the state by Friday and nearing an inch in northwestern
Utah. This will slowly lead to a transition from wind as the
primary thunderstorm threat midweek to locally heavy rain late in
the week and early in the weekend. With that, also expecting an
increase in thunderstorm coverage as the environment becomes more
favorable with mid-level cooling and by Friday, the arrival of PVA
from a dissipating shortwave trough diving into the northwestern
corner of the forecast area.

Thursday afternoon's expanded thunderstorm coverage will give way
to continued showers overnight, and increasing in coverage once
again Friday. Areas where a break in cloud cover allows for
surface heating through the morning are most suspect for more
vigorous convection, but won't be necessary as much of the state
will see showers trigger off the terrain as well as on broad
synoptic lift. Not expecting anything incredibly impactful, but
slow enough storm motions and southeasterly steering flow setting
up by Friday afternoon will set the stage for increased flash
flood potential if storms are able to initiate and track over
highly sensitive areas in particular.

.LONG TERM (After 12Z/6AM Saturday)...The extended forecast period
looks to remain active and wet over Utah and SW Wyoming. With a
broad longwave trough continuing to eject waves over the region,
coupled with growing cyclonic flow and synoptic forcing we will
continue to see the potential for PM showers and storms. Consensus
continues to grow on this feature weakening over the region and
giving way to another low pressure system that will move off the
Pacific and position itself over the SW CONUS by midweek of the
upcoming work week.

With the position of the current low just to the SW of our CWA it is
expected to move northeastward and drive an interesting flow regime
over Utah and SW Wyoming. Its more southern extent will give it
access to larger volumes of moisture with PWAT values expected to be
up to 200% of the climatological norms for this time of spring.
Convective initiation will remain to start around the early afternoon
hours after sufficient daytime heating allows for development. With
the flow regime changing to more E/SE its likely that most initiation
will be off the high terrain and either fading or enhancing into
valleys. In addition to the potential for gusty outflow winds and
lightning, weak deep layer flow overall will yield somewhat slow
storm motions. As a result, periodic heavy rainfall associated with
convection will remain a potential hazard to monitor for sensitive
locations such as burn scars, normally dry washes, slot canyons, and
slickrock areas.

Warming aloft into the weekend will bring highs to their warmest
during the period with many valleys reaching the 80s while far SW
Utah hits the 90s. This could vary among cloud coverage from storms
and showers however. We will continue to monitor the development of
the next low as it moves onshore by midweek and likely keeps the
active and wet forecast.

&&

.AVIATION...KSLC...Isolated afternoon convection will create brief
gusty/erratic winds and lightning before 00Z. Otherwise, VFR
conditions with some scattered high clouds and northerly winds
transitioning to southerly winds overnight.

.REST OF UTAH AND SOUTHWEST WYOMING...Isolated afternoon convection
over the entire region ending after 03Z. Any storms have the
potential to contain gusty/erratic winds and lightning. Otherwise,
VFR conditions with some scattered high clouds and diurnally driven
winds.

&&

.FIRE WEATHER...Little change in the forecast with confidence
remaining high that moisture and instability will increase over
the region through Friday and potentially carry through the
weekend. A slow-moving trough will meander eastward from central-
southern California and into the Great Basin, bringing with it the
potential for more widespread and organized precipitation in the
form of showers, thunderstorms, and by Friday the potential for
more steady banded and terrain-driven precipitation. As a result,
chances for gusty winds as well as wetting rain with thunderstorms
will be heightened through the forecast period. By Saturday, a
southeasterly flow regime is expected to set up, more like what is
typically seen with the late summer southwestern monsoon. As a
result of the uptick in low level moisture, afternoon relative
humidity will generally remain greater than 30 percent statewide
through the forecast period.

&&

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

Wessler/Selbig/Mahan

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http://weather.gov/saltlakecity