Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
346 AM MDT Sun Oct 2 2022

.SYNOPSIS...Unsettled weather will continue across portions of
southern and eastern Utah through Monday. Upper level ridging
will build into the region Tuesday and persist through much of
the remainder of the week.

&&

.SHORT TERM (Through 12Z Tuesday)...Another day, same upper level
low now located near the Yellowstone region. Morning upper air and
satellite analysis clearly depicts this ~570 dam low gradually
lifting subtly north and east. Meanwhile, a litany of shortwave
troughs continue to rotate around the parent circulation with two
of the most notable of these shortwave troughs currently crossing
west central Nevada and northern Nevada.

Radar across the region currently shows an area of light rain
showers across northern Utah from roughly Ogden to Provo and east.
Earlier relatively strong convection is located across far
eastern Utah into western Colorado. Very strong convection, with
some supercells, resulted in numerous flash flood warnings and
severe thunderstorm warnings across southeastern Utah Saturday.

Today's main threats will be both flash flooding and strong to at
times severe convection once again. By afternoon, HREF ensemble
mean SBCAPE values will range from around 750 J/kg in the southeast
to near or above 1250 J/kg in the southwest. Deep layer shear is
a bit less over yesterday's values, around 20-30 kts. Storm
motions will favor an east to at times southeast direction, which
is favorable for any of the north to south running drainages
across the Grand Staircase/Escalante National Monument, the Swell
and Capitol Reef.

A few things to tease out in the CAMs for this forecast. Looking
at the HREF, the FV3 core is substantially more robust with hourly
precipitation across southwestern Utah this morning, while most
of the other members are resolving lower precipitation amounts. In
general, the CAMs highlight an area of significant convection
across the Utah/Arizona border by early afternoon, spreading into
the Glen Canyon area through the day, with additional convection
across much of the remainder of central and southern Utah. While
the highest available atmospheric moisture is pinned to the lower
valley locations of far southern Utah, anomalously high for
October available atmospheric moisture continues across much of
the southern half of Utah. Add in the potential for organized
convection across this same area, which would be capable of higher
precipitation rates in addition to small hail and gusty
winds...and you have a increased threat for both severe convection
and flash flooding.

Where the highest flash flood threat will be is a waiting game as
the newest CAMs come in this morning, combined with more precise
timing of the previously mentioned shortwaves. Overnight HRRR runs
are persistent in the development of convection later this
morning across the southern tier near the Arizona border with
strong, widespread convection developing and shifting to eastern
Utah by afternoon. Early review of the 06Z CAMs indicates a shift
toward the HRRR solution for several additional models.

So what's the ultimate summary of the above paragraphs? Expect an
enhanced flash flood threat across much of central and southern
Utah, especially from Zion National Park, to the Grand Staircase,
east to Glen Canyon Rec Area...Capitol Reef and the Swell today.
Debated issuing a flood watch with this package but with the
uncertainty expressed in the CAMs...decided to hold off. This does
not mean the threat isn't substantial and those with outdoor
plans that include normally dry washes, slick rock areas, slot
canyons, etc should monitor the weather and consider alternate
activities for their Sunday afternoon and evening (across central
and southern Utah).

Another round of convection is expected Monday as a trailing
shortwave digs into central Utah/Nevada. This convection looks to
be more poorly forced...with a decreased threat of flash
flooding...but something to be monitored as model to model and
run to run consistency has been below average with this feature.

Current outlook from the Storm Prediction Center indicates much of
eastern Utah with a marginal risk for severe thunderstorms today.
In addition, WPC has issued a slight risk for flash flooding
across southern Utah today. These correlate well with the current
forecast and represent a reasonable description of the risk of
both phenomena across Utah today.

.LONG TERM (After 12Z Tuesday)...Rising heights ahead of a
building ridge will lead to a much quieter midweek period. Given
ensemble trends away from anomalous ridging, only expecting the
warmest days (Friday and Saturday) to be 5-10F above seasonal
normals across central and northern Utah at most. While sky cover
and wind gusts will vary day to day, expect generally pleasant
weather through Friday.

By Saturday, seeing evidence of a trough moving over top of the
ridge and amplifying down its eastern edge as it progresses into the
Great Basin in ~40% of the ensemble membership. The two clusters
that comprise this scenario are made up of a reasonable mix of CMCE,
GEFS, and EPS members and worth consideration, and have chosen to
leave NBM PoPS of 20-30% across southern Utah as-is for the upcoming
weekend. That said, this collection of ensemble members are
unenthusiastic about the available moisture with this potential
system, producing less than a tenth of an inch in any outcome.

&&

.AVIATION...KSLC...Light showers in the vicinity this morning are
expected to continue as yet another boundary pushes in from the
northwest. While winds may remain variable in direction until mid-
morning as a result, they should remain light, under 5 kts. By
18Z the boundary will have cleared the area and fair weather is
expected, with any convection likely to remain to the south and
east of the terminal. VFR conditions are expected, though a cloud
deck may develop near 8-10kft adjacent to the Wasatch.

.REST OF UTAH AND SOUTHWEST WYOMING...Active weather is expected
for much of the forecast area today, with the exception being much
quieter conditions to the west of I-15 and north of I-80. Showers
and thunderstorms across central and southern Utah are likely to
produce strong wind gusts in their vicinity, and in far southern
Utah these are likely to produce locally heavy rainfall. Elevated
convection is already ongoing early this morning and is expected
to fill in throughout the morning, reach its maximum coverage mid-
day, then taper off through the evening, perhaps lingering into
the overnight hours. VFR conditions are expected with the
exception of thunderstorms on station driving brief periods of
MVFR to IFR.

&&

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

Kruse/Wessler

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

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php

Special Weather Statement
National Weather Service Salt Lake City UT
1243 PM MDT Sun Oct 2 2022

UTZ124-128-021930-
South Central Utah UT-Zion National Park UT-
1243 PM MDT Sun Oct 2 2022

...A strong thunderstorm will impact portions of southeastern
Washington County through 130 PM MDT...

At 1243 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles southwest of Apple Valley, or 11 miles west of Colorado City,
moving northeast at 15 mph.

HAZARD...Penny size hail.

SOURCE...Radar indicated.

IMPACT...Minor damage to outdoor objects is possible.

Locations impacted include...
Apple Valley, Hildale and Rockville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3700 11325 3715 11314 3715 11295 3711 11293
      3700 11296
TIME...MOT...LOC 1843Z 239DEG 14KT 3700 11319

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...<40 MPH

STW

Special Weather Statement
National Weather Service Salt Lake City UT
1253 PM MDT Sun Oct 2 2022

UTZ122-125-021930-
Southwest Utah UT-Southern Mountains UT-
1253 PM MDT Sun Oct 2 2022

...A strong thunderstorm will impact portions of east central Iron
County through 130 PM MDT...

At 1252 PM MDT, Doppler radar was tracking a strong thunderstorm near
Enoch, or 10 miles northeast of Cedar City, moving east at 10 mph.

HAZARD...Half inch hail.

SOURCE...Radar indicated.

IMPACT...Minor damage to outdoor objects is possible.

Locations impacted include...
Parowan, Paragonah and Summit.

This includes Interstate 15 between mile markers 68 and 83.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3778 11307 3785 11307 3791 11298 3797 11277
      3778 11277
TIME...MOT...LOC 1852Z 255DEG 10KT 3783 11299

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...<40 MPH

STW

Special Weather Statement
National Weather Service Salt Lake City UT
1259 PM MDT Sun Oct 2 2022

UTZ117-021930-
Central Mountains UT-
1259 PM MDT Sun Oct 2 2022

...A strong thunderstorm will impact portions of east central Sevier
County through 130 PM MDT...

At 1258 PM MDT, Doppler radar was tracking a strong thunderstorm 14
miles southeast of Salina, or 20 miles east of Richfield, moving east
at 10 mph.

HAZARD...Half inch hail.

SOURCE...Radar indicated.

IMPACT...Minor damage to outdoor objects is possible.

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

This includes Interstate 70 between mile markers 74 and 85.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3870 11177 3880 11180 3891 11148 3870 11144
TIME...MOT...LOC 1858Z 255DEG 10KT 3876 11171

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...<40 MPH

STW

Special Weather Statement
National Weather Service Salt Lake City UT
105 PM MDT Sun Oct 2 2022

UTZ122-021930-
Southwest Utah UT-
105 PM MDT Sun Oct 2 2022

...A strong thunderstorm will impact portions of central Beaver
County through 130 PM MDT...

At 104 PM MDT, Doppler radar was tracking a strong thunderstorm 16
miles west of Milford, moving east at 10 mph.

HAZARD...Half inch hail.

SOURCE...Radar indicated.

IMPACT...Minor damage to outdoor objects is possible.

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

This includes Utah Route 21 between mile markers 58 and 70.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3832 11337 3843 11337 3854 11313 3830 11310
TIME...MOT...LOC 1904Z 255DEG 10KT 3837 11332

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...<40 MPH

STW

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