Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
403 PM MDT Fri Jul 23 2021

.SYNOPSIS...A dry westerly flow will spread over northern Utah
through the weekend, while deep moisture will linger across the
south leading to daily showers and thunderstorms with localized
heavy rainfall. The ridge providing dry weather for northern Utah
will move east by early next week which will open the door for
moist southerly flow to move back across most of the forecast
area.

&&

.SHORT TERM (Through 12Z Monday)...Despite drier air moving in
across northern Utah today, there remains enough low level
moisture to generate some decent thunderstorms over the Raft River
Range this afternoon producing strong winds and heavy rain.
However, models are showing that subsidence near the 500mb level
will become stronger and deeper later this afternoon and evening
across northern Utah which should put a cap to thunderstorm
development, so expecting any storms to die off fast early this
evening. Drier air will continue to spread in across the remainder
of northern Utah and Uinta County Wyoming tonight through
Saturday, but the ridge will move east by Sunday pushing the
subsidence portion of the ridge to our east and allow convection
to once again develop over the Uintas by Sunday afternoon and
evening. Moisture will be marginal at this time.

Central Utah will dry a little more Saturday as the westerly to
northwesterly flow penetrates this portion of the state, but the
hiatus in thunderstorms will be short lived as convection will be
on the increased Sunday over the central mountains.

Light northerly flow over most of southern Utah combined with deep
moisture will have thunderstorms capable of producing heavy rain
to move down drainage exacerbating the potential for flash
flooding. A flash flood watch remains in effect until midnight as
storms over the higher terrain will drift southward this evening.
St. George will have a good chance of having a cluster of
thunderstorms move south southwest across them this evening as
some high resolution models are in agreement on an instability
bullseye over Washington County this evening. The northerly flow
will continue through Saturday so the threat of flash flooding
will continue, especially in the drainages that drain southward.
By Sunday the ridge aloft will have moved east and the flow turns
southeast importing moisture northward.

Temperatures will average a few degrees above average in the north
with temperatures averaging a few degrees below normal in the
south due to clouds and thunderstorms.

.LONG TERM (After 12Z Monday)...The low moving through New Mexico
and Arizona over the weekend responsible for transitioning winds
to more a of a northeasterly flow will exit to the west. That will
allow for southerly flow to kick back in as the ridge centers to
the east. Better moisture advection will build in from that
direction, especially in northern Utah. Elsewhere, precipitable
water values will stay similar from the remnant moisture
associated with the aforementioned low along with more monsoonal
moisture. Values around 1" or higher could build into central
Utah. In northern Utah, values will likely surpass that mark
Tuesday as conditions remain largely unchanged. Flash flooding
will remain a threat. The storms will be similar to recent ones,
aided by daytime heating and diminishing with loss of solar
warming.

Variations in the ridge position will influence PoPs each day in the
forecast, but there's good confidence in the monsoonal set up
remaining in place.

The warmest temperatures of the week in southwest Wyoming and
northern Utah are expected near the start, when the driest
conditions are in place. Highs around 5F warmer than average are
expected Monday, followed by slightly cooler, but still near average
temperatures through Friday. Temperatures will mainly be around 5F
cooler to near average in central and southern Utah.

&&

.AVIATION... KSLC...VFR conditions are expected through the valid
TAF period. Scattered mid and high clouds will decrease into the
evening, but smoke will increase from the northwest. Visby is
expected to remain above P6SM. Winds will switch to southeast
around 04Z.

Rest of Utah and southwest Wyoming...VFR conditions are expected
through the valid TAF period. Isolated showers and thunderstorms
will diminish in southwest Wyoming and northern Utah around 00Z. The
chance for precipitation will last through 06Z in southern Utah,
with heavy rain the main threat. A shower or thunderstorm over a TAF
site could drop CIGs into MVFR range for a short amount of time.
Smoke will increase in southwest Wyoming and northern Utah into
Saturday, but visby is expected to remain above P6SM.

&&

.FIRE WEATHER...The drier westerly flow has started to move in across
the north today and will penetrate farther into central Utah this
weekend, eliminating most thunderstorm activity in the north and
reducing the threat of thunderstorms in the central area. Min RHs
will fall below 15% in the north and some western valleys this
weekend, but then trend upward as the flow switches to southerly
by early next week importing more moisture and increasing chances
of showers and thunderstorms.

Deep moisture will remain over southern Utah, although it will be
suppressed a little farther south Saturday than today, but then
start spreading northward some Sunday and more so by Monday
reaching fwx zone 492, and northeast into the Uintas. Widespread
showers and thunderstorms are expected over the far southern fwx
zones Saturday through Tuesday, while scattered showers and
thunderstorms will be common just north of here on Saturday and
into central Utah Sunday and Monday. RH values will remain
elevated through the entire forecast period with min RH values in
the 30-40% range with max RH values above 80% in many areas.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch until midnight MDT tonight for UTZ122>125-128.

WY...None

&&

SHORT TERM...Struthwolf
LONG TERM...Wilson
AVIATION...Wilson
FIRE WEATHER...Struthwolf

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

Hazardous Weather Outlook
National Weather Service Salt Lake City UT
619 AM MDT Fri Jul 23 2021

UTZ101>131-WYZ021-241300-
Great Salt Lake Desert and Mountains-Tooele and Rush Valleys-
Eastern Box Elder County-Northern Wasatch Front-Salt Lake Valley-
Utah Valley-Cache Valley/Utah Portion-Wasatch Back-
Bear Lake and Bear River Valley-Wasatch Mountains I-80 North-
Wasatch Mountains South of I-80-Western Uinta Mountains-
Wasatch Plateau/Book Cliffs-Western Uinta Basin-
Western Millard and Juab Counties-Eastern Juab/Millard Counties-
Central Mountains-Sanpete Valley-Sevier Valley-Castle Country-
San Rafael Swell-Southwest Utah-Lower Washington County-
Zion National Park-Southern Mountains-Upper Sevier River Valleys-
Bryce Canyon Country-South Central Utah-
Capitol Reef National Park and Vicinity-Western Canyonlands-
Glen Canyon Recreation Area/Lake Powell-Southwest Wyoming-
619 AM MDT Fri Jul 23 2021

This Hazardous Weather Outlook is for the western two thirds of
Utah and southwest Wyoming.

.DAY ONE...Today and Tonight

Showers and thunderstorms capable of producing heavy rain, gusty
winds, and small hail will develop once again this afternoon and
evening. The strongest storms are expected across southern
Utah where a potential for flash flooding exists, especially in
prone areas such as slot canyons, burn scars, areas of steep
terrain, and normally dry washes and streams.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Daily showers and thunderstorms will be capable of heavy rain,
gusty winds and small hail each afternoon and evening. These
showers and thunderstorms will be more confined to southern Utah
Saturday and Sunday before spreading north again for the first
half of the upcoming week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please relay any information
about observed severe weather to the NWS while following all
local, state, and CDC guidelines.

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

For information on potential road travel impacts visit...
http://www.udottraffic.utah.gov/roadweatherforecast.aspx

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
221 PM MDT FRI JUL 23 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0230 PM     LIGHTNING        SAINT GEORGE            37.11N 113.58W
07/22/2021                   WASHINGTON         UT   NEWSPAPER

            A LIGHTNING BOLT BLEW A FOUR FOOT WIDE HOLE
            THROUGH THE ROOF OF A ST. GEORGE HOME,
            STARTING A FIRE. NO ONE WAS HURT.

0706 PM     TSTM WND DMG     1 ESE MIDVALE           40.61N 111.89W
07/22/2021                   SALT LAKE          UT   PUBLIC

            1-INCH TREE LIMBS BROKEN; SHINGLES BLOWN
            OFF.

0715 PM     TSTM WND DMG     1 N TAYLORSVILLE        40.68N 111.93W
07/22/2021                   SALT LAKE          UT   PUBLIC

            BROKEN TREE LIMBS CAUSED DAMAGE.

0715 PM     HAIL             4 SSE SLC INTL ARPT     40.73N 111.95W
07/22/2021  M0.75 INCH       SALT LAKE          UT   BROADCAST MEDIA

            REPORTED FROM ABC 4 STUDIOS.

0715 PM     TSTM WND DMG     1 N COTTONWOOD HEIGHTS  40.62N 111.81W
07/22/2021                   SALT LAKE          UT   PUBLIC

            A LARGE TREE HAS UPROOTED AND CRASHED INTO A
            HOME, PLACING A HOLE IN THE ROOF. DAMAGE TO
            AN AWNING IS ALSO NOTED. TIME ESTIMATED FROM
            RADAR.

0730 PM     TSTM WND DMG     1 N MURRAY              40.67N 111.89W
07/22/2021                   SALT LAKE          UT   PUBLIC

            POWER LINES BROKEN. MULTIPLE LARGE TREES
            HAVE BEEN UPROOTED THROUGHOUT TOWN. REPORTS
            OF CARPORT AND CAR DAMAGE, DAMAGE TO
            BUSINESS SIGNS AND ROOFTOPS.

&&

Special Weather Statement
National Weather Service Salt Lake City UT
314 PM MDT Fri Jul 23 2021

UTZ122-125-232200-
Southwest Utah UT-Southern Mountains UT-
314 PM MDT Fri Jul 23 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN IRON COUNTY UNTIL 400 PM
MDT...

At 314 PM MDT, National Weather Service Doppler radar indicated
strong thunderstorms along a line extending from 19 miles northwest
of Paragonah to 23 miles east of Eagle Valley...and moving east at 25
mph.

Pea size hail and wind gusts of 40 to 55 mph will be possible.

Locations impacted include...
Lund.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Salt Lake City.

&&

LAT...LON 3806 11268 3782 11345 3799 11395 3814 11315
TIME...MOT...LOC 2114Z 274DEG 22KT 3810 11301 3795 11377

MT

Special Weather Statement
National Weather Service Salt Lake City UT
327 PM MDT Fri Jul 23 2021

UTZ101-232200-
Great Salt Lake Desert and Mountains UT-
327 PM MDT Fri Jul 23 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN BOX ELDER COUNTY
UNTIL 400 PM MDT...

At 326 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm near Park Valley, or 27 miles south of Malta...
moving northeast at 25 mph.

Penny to nickel size hail and wind gusts of 40 to 55 mph will be
possible.

Locations impacted include...
Park Valley, Curlew Junction, Rosette and Standrod.

This includes Utah Route 30 between mile markers 40 and 60, and
between mile markers 69 and 77.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

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

&&

LAT...LON 4163 11346 4178 11361 4200 11341 4199 11298
TIME...MOT...LOC 2126Z 221DEG 22KT 4190 11333

MT

Special Weather Statement
National Weather Service Salt Lake City UT
331 PM MDT Fri Jul 23 2021

UTZ103-107-110-232200-
Eastern Box Elder County UT-Wasatch Mountains I-80 North UT-
Cache Valley/Utah Portion UT-
331 PM MDT Fri Jul 23 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN CACHE AND
NORTHEASTERN BOX ELDER COUNTIES UNTIL 400 PM MDT...

At 331 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm near Plymouth, or 17 miles south of Malad...
moving north at 5 mph.

Pea size hail and wind gusts of 40 to 55 mph will be possible.

Locations impacted include...
Plymouth, Portage and Washakie.

This includes Interstate 15 between mile markers 390 and 400.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

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

&&

LAT...LON 4184 11211 4188 11234 4200 11234 4200 11202
TIME...MOT...LOC 2131Z 192DEG 5KT 4194 11221

MT

Special Weather Statement
National Weather Service Salt Lake City UT
404 PM MDT Fri Jul 23 2021

UTZ103-107-110-232230-
Eastern Box Elder County UT-Wasatch Mountains I-80 North UT-
Cache Valley/Utah Portion UT-
404 PM MDT Fri Jul 23 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN CACHE AND
NORTHEASTERN BOX ELDER COUNTIES UNTIL 430 PM MDT...

At 404 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm over Plymouth, or 12 miles north of Tremonton...
moving southeast at 10 mph.

Penny to nickel size hail and wind gusts up to 50 mph will be
possible.

Locations impacted include...
Tremonton, Cache, Smithfield, Clarkston, Trenton, Plymouth, Peter,
Riverside, Benson, Garland, Honeyville, Elwood, Newton, Amalga,
Fielding, Deweyville and Collinston.

This includes Interstate 15 between mile markers 384 and 395.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If threatening weather approaches, take shelter in a sturdy building.

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

&&

LAT...LON 4184 11227 4198 11212 4186 11183 4165 11207
TIME...MOT...LOC 2204Z 309DEG 8KT 4187 11212

MT