Severe Thunderstorm Warning 55, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
230 PM MDT Mon Aug 12 2024

.SYNOPSIS...Monsoonal moisture will remain over Utah and southwest
Wyoming for the early part of the weekend, bringing thunderstorms
capable of producing heavy rain and gusty winds. Drier air will
move in for the latter part of the week, with moisture possibly
returning by the weekend.

&&

.SHORT TERM (Through 12Z/6AM Wednesday)...

KEY MESSAGES:
- Scattered to numerous showers and thunderstorms are forecast
  across the northern two thirds of Utah tonight. Impacts of heavy
  rain and flash flooding are possible. Gusty winds of 60 mph are
  possible.
- Scattered to numerous showers and thunderstorms are forecast for
  Tuesday across much of the state with the exception of far
  western Utah. Impacts of heavy rain, flash flooding, gusty winds
  and hail are possible.

As anticipated, numerous thunderstorms has development in a very
moist laden environment across northern Utah this afternoon. Wind
gusts of 60 mph have already been observed across Tooele county
and other parts of the west desert tomorrow. PW values of 1.2 are
noted. Thunderstorm tops of 40,000 ft are being observed across
the west desert with the storms associated with the severe winds.
The environment for the remainder of the afternoon and into the
evening is quite favorable for persistent thunderstorm activity.
Effective bulk shear of 30 to 40 knots and favorable surface based
CAPE of around 2500 J/kg will sustain/promote strong
thunderstorms. There remains a 90 percent chance for wind gusts in
excess of 60 mph with a 70 percent chance for winds in excess of
50 mph.

Heavy rain with widespread forecast amounts over an inch are
forecast across much of central and southern Utah through this
evening. Rainfall rates of 1/2 inch to 1 inch per hour will not be
uncommon tonight. This again will lead to concerns for flash
flooding for burn scars in particular but localized urban flooding
also will be of concern. For central and southern Utah, threats
of heavy rain/flash flooding will remain for area slot canyons,
normally dry washes, creeks and streams, recent burn scars, and
other low-lying and flood-prone locations.

Overnight, another round of weaker showers and thunderstorms are
forecast to track through northern Utah. While some gusty winds
are possible, these storms are not likely to have too much impact
to the region aside from the gusts and briefly heavy rain.

Yet more showers and thunderstorms are expected for Tuesday. For
some, the rain may actually never really stop. It's just about
impossible to try to pinpoint for who and if that will really be
the case but essentially, this is a looking like a very wet
period. Gusty winds will once again be a threat tomorrow with
around a 70 percent chance for 50+ mph winds across eastern Utah.
Drying conditions are noted for the far western portion of western
Utah tomorrow.

.LONG TERM (After 12Z/6AM Wednesday), Issued 323 AM MDT...On
Wednesday an upper level jet max associated with an easterly
shifting trough will slide atop the forecast region. In
combination with the movement of the southern CONUS ridge,
moisture advection into the area will become less favorable, and
PWAT values will gradually fall back nearer to seasonal normal
values through the day. That said, remaining moisture in
combination with diurnal heating and synoptic support will be
sufficient to trigger isolated to scattered daytime convection
through northern and eastern Utah, as well as southwest Wyoming.
To that end, the signal for highest coverage is noted along the
high Uintas on into southwest Wyoming. With the stronger jet flow
aloft, shear values will once again be a bit elevated (deep layer
shear around 20-40 kts) which may help to generate some isolated
instances of stronger and more organized convection. As daytime
heating wanes and drying trend continues, lingering convection
will begin to fade late evening into the overnight hours.

Thursday and Friday look to be the quieter days of the forecast
period as positioning of the northern trough and southern ridge
remain less favorable for stronger moisture advection into the
region. To that end PWAT values to fall closer to 60-90% of normal
for mid August, and as such daily convective potential becomes much
more isolated in coverage. The best signal at the moment for a bit
more scattered activity is noted Thursday afternoon in the high
Uintas, southwest Wyoming, and areas near the Idaho/Utah border
where ensembles suggest PWATs may linger a bit closer to that 90%
side of the range. Friday appears to become even more isolated, with
any afternoon initiation more likely off of high terrain. Still,
given the stronger westerlies aloft, shear values will be a bit
elevated and any convection that manages to mature in the right
place could still manage to trend a bit on the strong side.

Moving into the weekend, ensemble guidance shows fairly good
consensus that the southern ridge will migrate back towards the Four
Corners to Southern Plains region while troughing amplifies through
the PacNW. While some mostly minor differences are noted in the
exact placement/strength of these features, the general setup will
help increase deeper south to southwesterly flow, in turn promoting
increased moisture transport back into the region. As a result,
forecast carries a return of daily isolated to scattered convective
chances, with coverage particularly favored across southern Utah as
well as generally along and east of the high terrain. Those with
weekend recreation plans that may take them to rain prone areas such
as slot canyons, typically dry washes, and slickrock areas will at
least want to keep an eye on the daily trends. While less likely,
there does remain a small subset (around 10%) of ensemble members
which favor a stronger ridge positioned nearer to the forecast
region, which would yield drier and warmer weather than currently
included with this forecast.

&&

.AVIATION...KSLC...Intermittent VFR/MVFR with isolated IFR
conditions through this evening as widespread convection and low
CIGs move through northern Utah. Isolated convection will become
more widespread by 22Z with a transition from strong convection
with frequent lightning, heavy rain, and gusty winds to more
stratiform convection containing lightning, rain, and winds with
decreasing intensity. Precipitation becomes more showery and
scattered after 03Z persisting through ~10Z. With precipitation,
CIGs will be ~5- 7kft creating mountain obscuration.

.REST OF UTAH AND SOUTHWEST WYOMING...Widespread convection across
the airspace will create intermittent MVFR/IFR as CIGs lower with
convective activity and create mountain obscuration. Highest precip
chances will be across central and northern portions of the
airspace. Strong convection with frequent lightning, heavy rain, and
gusty winds will gradually transition to more stratiform
precipitation after 03Z confined to the central/northern portions of
the airspace lasting through ~10Z. Synoptic winds will be breezy out
of the south before weakening overnight.

&&

.FIRE WEATHER...Wetting rains are expected across northern Utah and
the Uinta Basin this evening as a result of numerous showers and
thunderstorms in these areas. Isolated to scattered thunderstorms
will remain in the forecast even into the overnight hours for much of
the state with wetting rain potentials highest east of I-15. Additionally,
across much of western Utah tonight, gusty southerly winds are
anticipated.

For tomorrow, gusty southerly winds will generally be confined
to the southwest corner of Utah. An incoming trough will bring yet
another round of scattered to numerous showers and thunderstorms
to much of the state tomorrow. One area not favored for thunderstorm
development will be far western Utah where dryer conditions are
expected to begin working their way in.

Toward Wednesday and especially the latter half of the work week,
drying conditions are anticipated statewide. Critical dryness are
currently forecast for Thursday and Friday across much of western
Utah and for portions of southern Utah as well.

&&

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

SHORT TERM...NDeSmet
LONG TERM...Warthen
AVIATION...Mahan
FIRE WEATHER...NDeSmet

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

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