Severe Thunderstorm Warning 79, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
314 PM MDT Sun Aug 18 2024

.SYNOPSIS...Monsoonal moisture will remain in place through the
early part of the week before drier air moves in for Tuesday.
Another monsoon surge is expected Wednesday into the end of the
week.

&&

.SHORT TERM...Another monsoon thunderstorm day is underway for
much of the forecast area. Satellite analysis shows high pressure
in vicinity of north Texas with broad southerly flow over the
Four Corners states. This has brought PWATs over an inch to much
of Utah, including 1.2" to the Lake Powell vicinity. Satellite
products suggest this is running about 170% of normal. An MCV has
drifted northward across the UT/AZ border with the center of
circulation currently south of Escalante. Convective activity is
most pronounced on the western and northern periphery of this
feature, stretching from Washington County northeastward to the
Uintas. Overall, storms are more scattered than yesterday with
less instance rainfall rates, but still pose a flash flooding
threat in sensitive areas such as dry washes, slot canyons, and
recent burn scars. Severe potential meanwhile is somewhat
diminished vs yesterday with less synoptic level support, a bit
less shear, and a cap for surface-based convection. Nevertheless,
with mixed-layer CAPE of 1000 J/Kg across a broad area, we have
seen a few stronger cells capable of gusty winds and small hail in
addition to the heavy rain threat. Similar to what transpired in
northern Utah yesterday, areas behind the MCV that is rolling
through (generally south of the San Rafael Swell and east of
Kanab) will likely see clearing and more stable conditions after
it passes. Lastly, a bit of nocturnal convection lingering from
the evening into the early overnight hours is possible over
northern Utah, shifting eastward overnight.

One more day of scattered monsoonal showers/thunderstorms is in
store for Monday, though with reduced coverage of storms as PWAT
starts to decrease, dropping to an inch or less for most of the
forecast area.  Convection may also develop near
the moisture gradient across western Utah during the afternoon, with
activity waning during the late afternoon to evening hours.

.LONG TERM (After 12Z/6AM Tuesday), Issued 426 AM MDT...
While the long-term period begins fairly dry, another surge of
moisture will produce more showers and thunderstorms by the end of
the week. A closed low moving inland could bring cooler, drier
weather to the area next weekend.

Largely unchanged from previous forecasts, the longwave pattern
through at least Thursday features ridging to the east and a
developing trough over the PacNW. Though Monday will be quite active
once again, a subtle change in flow direction to more westerly will
allow drier air to move into the area for Tuesday, especially across
the north. Models have trended even drier since yesterday; thus,
precipitation chances are now limited to higher terrain of southern
UT, mainly near the Boulder Mtn/Capitol Reef area. Moisture then
will start to make its return on Wednesday, expanding those
precipitation chances further north and west. These chances will
further expand in coverage and intensity heading into Thursday and
Friday with additional moisture advection from the south.

Our attention then turns to this trough developing into a strong
closed low along the west coast. There is still plenty of
uncertainty in its progression eastward, though ensemble guidance
suggests it could take a track towards northern UT/northeastern
Great Basin sometime between Friday and Sunday. If the closed low
takes this track, we could see a "cold" front like deterministic
solutions are suggesting..."cold" being relative. Ahead of this
front, strong southwesterly winds are possible, accompanied by more
organized convection given increased shear. This front would then
produce a transition to a much drier air mass and below-normal
temperatures. Keep in mind that this is still 5-7 days out, and the
track of this low could shift elsewhere.

&&

.AVIATION...KSLC...Showers and thunderstorms capable of gusty,
erratic outflow winds, and locally heavy rain are likely from 21-
06Z. Southeast winds, with gusts around 20 knots will prevail, but
wind speeds and directions will be influenced by showers and
thunderstorms. Light southeast winds with dry conditions will
prevail once showers and thunderstorms taper off, with scattered
showers and thunderstorms by around 20Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Showers and thunderstorms
capable of gusty, erratic outflow winds and locally heavy rain will
track from southwest to northeast through the evening. Prevailing
winds will primarily be from the south, with gusts around 20 knots,
but outflow winds will influence wind speeds and directions,
especially from 21-06Z. Dry conditions will last through the
morning, with scattered showers and thunderstorms after 19Z.

&&

.FIRE WEATHER...A moist airmass will remain in place over the area
through Monday, drying slightly but still moist enough to bring a
continued threat of showers and thunderstorms to the area. Many
of these storms will be capable of producing wetting rain, with
locally heavy rain possible. Gusty winds may also accompany
thunderstorms, but gusts over 45 mph will be isolated.

The airmass will see more significant drying by Tuesday, limiting
the extent of any convection. Drier southwesterly flow across
western Utah will bring marginal critical fire weather conditions
Tuesday into Wednesday. For Wednesday in particular, some forecast
guidance is indicating that single digit RHs could shift as far
east as the I-15 corridor. Combined with breezy southwest winds,
this could bring isolated areas of critical fire weather
conditions, depending on fuels. Moisture then starts to return to
the area for the second half of the week, with cooler conditions
appearing more likely by next weekend.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flood Watch until 10 PM MDT this evening for UTZ113-117-123>126-
     128-129-131.

WY...None.
&&

Van Cleave/Cunningham/Wilson

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

Special Weather Statement
National Weather Service Salt Lake City UT
321 PM MDT Sun Aug 18 2024

UTZ115-182200-
Western Millard and Juab Counties UT-
321 PM MDT Sun Aug 18 2024

...A strong thunderstorm will impact portions of central Juab County
through 400 PM MDT
...

At 321 PM MDT, Doppler radar was tracking a strong thunderstorm 20
miles southeast of Fish Springs Wildlife Refuge, or 35 miles
northwest of Delta, moving northeast at 20 mph.

HAZARD...Wind gusts up to 50 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This storm will remain over mainly rural areas of central Juab
County.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3954 11305 3959 11328 3990 11314 3975 11277
TIME...MOT...LOC 2121Z 215DEG 17KT 3964 11311

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH

HM

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