Severe Thunderstorm Warning 18, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
348 AM MDT Thu Jun 30 2022

.SYNOPSIS...A monsoon surge will continue to bring the threat of
heavy rain to Utah this afternoon and evening, mainly south and
east of the I-15/US-6 corridor. Thunderstorms will be capable of
gusty winds north and west of this area. A drier airmass will
gradually shift into the state Friday into Saturday, bringing an
end to the monsoon surge and ushering in the threat of critical
fire weather conditions Saturday into early next week.

&&

.SHORT TERM (Through 12Z Sunday)...Another active day is in store
across the CWA. Morning upper air and satellite analysis indicate
zonal flow continues across the northern tier of the West, with a
trough approaching the Pacific Coast. Meanwhile, a notable monsoon
surge is present from western Mexico, through the 4-Corners into
Colorado. There may be some interplay between several weak
disturbances along the ITCZ and northward moisture transport into
the monsoonal trough along the west coast of Mexico.

Current mesoanalysis indicates weak convergence across northern
Utah, focused on the Tooele and Salt Lake Valleys. Observations
suggest a stable layer is present in these locations near the
surface, though sufficient instability is available for elevated
convection near and along this convergence zone from roughly
Dugway to Tooele to Salt Lake City to near Evanston. This trend is
noted in model soundings as well. Given the elevated nature of
the convection, do not expect much threat of wind gusts but rather
locally heavy rain and thunder causing early wake ups for those
in the Tooele and Salt Lake Valleys.

Looking at the evolution of convection today, expect SBCAPE near
500-1000 J/kg across much of the state. Per expected, with an
upper level trough approaching the Pacific Coast, wind shear will
be higher across northern and western portions of the CWA, where
the most significant threat will be gusty winds...especially
toward Evanston and the Uinta Mountains. Small hail cannot be
ruled out as convection may show at least periodic organization.

Further south (mainly south and east of US-6/I-15), with weaker
steering flow, expect the main threat with convection this
afternoon and evening to be heavy rain. Current storm motion
analysis indicates a tendency toward storm motions toward the east
to east-southeast. Expect convection to develop on the higher
terrain and shift to the adjacent valleys this afternoon into the
evening. There may be some training in related to the convection
as well. Given the storm motions will support down drainage motion
in portions of Capitol Reef, the Grand Staircase-Escalante
National Monument, the slot canyons near the headwaters of the
Paria River as well as the San Rafael Swell (including Goblin
Valley/Little Wildhorse area), flash flood potential will be
heightened. Current Flood Watch looks good and will cover these
areas.

As the Pacific trough shifts eastward Friday, expect drier
southwesterly flow to build into western Utah. Expect relatively
weak convection from the higher terrain eastward, though the
threat of flash flooding looks to be lower than Thursday. Dry air
advection will continue to progress eastward by Saturday,
relegating convection to mainly higher terrain areas of northern
Utah Saturday afternoon and evening. By this time, the threat for
critical fire weather conditions will increase across western
Utah. For more information on the fire weather threat, see the
fire weather discussion.

.LONG TERM (After 12Z Sunday)...There is good model agreement in
a trough positioned over the PacNW early Sunday. This will result in
continued eastward progression of the ridge and largely dry
conditions locally with monsoonal moisture advection further east.
The pressure gradient will strengthen with the approaching trough,
resulting in enhanced southwest flow. Very dry conditions, with
gusts mixing to the surface upwards of 30 knots are expected across
western Utah. Winds will be slightly lower further north, with
gusts reaching around 30 knots, but similar relative humidity
values are expected.

The trough is not expected to totally break down the ridge, but
rather push it eastward while lifting northward. This will keep
enhanced southwest winds throughout southwest Wyoming and Utah for
Monday. Ensemble and deterministic models have a shallow cold front
moving into Utah Monday morning. Conditions will stay dry, but it
will drop temperatures a few degrees. Slightly higher relative
humidity values are expected with that, but most places will have
minimum values in the teens. Similar wind speeds from Sunday are
expected, with high fire danger for much of Utah.

The trough will lift northward Tuesday as heights build from east to
west with a retrograding ridge. Much lighter wind speeds will
follow. Ensemble guidance is in good agreement of the ridge
retrograding enough that flow for monsoonal moisture will not be
into Utah. This will result in dry conditions likely all week with
temperatures of 5-10F warmer than average much of the week, peaking
later in the week.

&&

.HYDROLOGY...The monsoon surge continues, with relatively high
precipitable water values across southern and eastern Utah. Storm
motion will favor a east to east-southeast trajectory this
afternoon and evening. With a decrease in overall storm motion,
combined with the potential for training in vulnerable areas,
expect an increase concern of flash flooding through slot canyons,
normally dry washes, and slickrock areas in southern and eastern
Utah. Highest threat areas will be the San Rafael Swell including
the Goblin Valley area, Capitol Reef National Park, the Grand
Staircase- Escalante National Monument as well as slot canyon
areas near the headwaters of the Paria River and near US-95 north
and east of the Henrys.

&&

.AVIATION...KSLC...Conditions will transition drier with showers
and thunderstorms diminishing around sunrise. That will last
through the morning with light southeast winds. Scattered showers
and thunderstorms are expected from around 19Z through the much of
the evening. Light rainfall is expected with any storms, but
enhanced, erratic outflow wind gusts are expected to be the
biggest threat.

.REST OF UTAH AND SOUTHWEST WYOMING...Largely dry conditions will
last through the morning. Scattered afternoon showers and
thunderstorms are likely for southwest Wyoming and much of Utah
with enhanced, erratic outflow winds. Showers and thunderstorms
are expected to taper off by around 06Z.

&&

.FIRE WEATHER...With mid and low level moisture continuing to
increase today, expect another round of mainly wet thunderstorms
with the potential for heavy rain mainly south of US-6 and east of
I-15 today. Any thunderstorms north of that area will be capable
of gusty and erratic winds. A drier airmass will build into the
western portion of the state Friday, shifting across the entire
state by Saturday.

As a trough approaches the Pacific Coast, expect winds to
increase across the western zones Saturday. This, combined with
much drier conditions, may bring a round of critical fire weather
conditions to the western zones. Gusty winds look to expand
further Sunday, bringing the potential for critical fire weather
conditions further north and east Sunday afternoon and evening.
This may continue into Monday.

The drier pattern looks to continue into at least early to mid
week next week as broad, persistent high pressure remains in place
across the West.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flood Watch from noon MDT today through this evening for UTZ121-
     128>131.

WY...None.
&&

Kruse/Wilson

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
1245 PM MDT Thu Jun 30 2022

UTZ112-WYZ021-301930-
Western Uinta Mountains UT-Southwest Wyoming WY-
1245 PM MDT Thu Jun 30 2022

...A strong thunderstorm will impact portions of northeastern Summit
and southeastern Uinta Counties through 130 PM MDT...

At 1245 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles southwest of Robertson, or 27 miles southeast of Evanston,
moving northeast at 15 mph.

HAZARD...Wind gusts up to 50 mph and pea size hail.

SOURCE...Radar indicated.

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

Locations impacted include...
Robertson, Lonetree and Mountain View.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4099 11056 4112 11062 4130 11028 4100 11008
TIME...MOT...LOC 1845Z 238DEG 12KT 4108 11049

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

Webber

Special Weather Statement
National Weather Service Salt Lake City UT
147 PM MDT Thu Jun 30 2022

UTZ125-128>130-302030-
Capitol Reef National Park and Vicinity UT-South Central Utah UT-
Western Canyonlands UT-Southern Mountains UT-
147 PM MDT Thu Jun 30 2022

...A strong thunderstorm will impact portions of central Garfield
County through 230 PM MDT...

At 147 PM MDT, Doppler radar was tracking a strong thunderstorm near
Boulder, or 15 miles northeast of Escalante, moving east at 20 mph.

HAZARD...Wind gusts of 50 to 55 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.

Locations impacted include...
Boulder.

This includes Utah Route 12 between mile markers 73 and 100.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3776 11147 3797 11156 3812 11108 3784 11097
TIME...MOT...LOC 1947Z 249DEG 16KT 3789 11137

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...55 MPH

Webber

Special Weather Statement
National Weather Service Salt Lake City UT
240 PM MDT Thu Jun 30 2022

UTZ112-WYZ021-302130-
Western Uinta Mountains UT-Southwest Wyoming WY-
240 PM MDT Thu Jun 30 2022

...A strong thunderstorm will impact portions of east central Summit
and southeastern Uinta Counties through 330 PM MDT...

At 240 PM MDT, Doppler radar was tracking a strong thunderstorm 18
miles southwest of Robertson, or 24 miles southeast of Evanston,
moving east at 25 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.

Locations impacted include...
Robertson.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4091 11079 4105 11083 4122 11029 4095 11018
TIME...MOT...LOC 2040Z 253DEG 21KT 4099 11067

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

Webber

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