Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
955 AM MDT Sat Jul 31 2021

.SYNOPSIS...Deep moisture will remain across Utah and southwest
Wyoming through the weekend. This will result in an extended
period of thunderstorm chances with a heavy rain threat, along
with temperatures trending slightly below normal. A warming and
drying trend is anticipated by midweek.

&&

.DISCUSSION...A moist southerly flow remains in place over Utah
and southwest Wyoming this morning with a ridge centered just east
of the area. Precipitable water values range from 0.8 inch over
the higher terrain to 1.2 to 1.4 inch over most valley locations.
This is more than enough to see another round of convective
development this afternoon, primarily focused over the higher
terrain due to a lack of a well defined forcing mechanism.
However, will likely see at least some storms drift into the
valleys late this afternoon into early this evening. Given the
lack of shear, not anticipating much in the way of organized or
long lived convection, and upstream storm motion due to the
southerly flow decreases the flash flood threat a bit. Still,
heavy rain is likely with any storms that develop. Clouds and
moisture across the area will keep maxes today near or just below
seasonal normals.

Sunday is anticipated to be an even more active day for convection
as weak shortwave energy currently over the Great Basin lifts
northward and moves across northern Utah through Monday. This
feature will provide additional instability and increase available
shear. With more widespread and potentially longer lived
convection, expecting the flash flooding threat to increase and
will need to consider a Flash Flood Watch with the afternoon
package. Focus of convection will shift to northern portions of
the forecast area Monday as the wave continues to lift northward
and a drier west to northwest flow develops behind it as high
pressure builds over the Great Basin. With this pattern change, a
drying and warming trend should continue for the middle to latter
part of the upcoming week.

No updates expected to the forecast this morning.

&&

.AVIATION...KSLC...VFR conditions will prevail at the SLC terminal
through the afternoon with light winds shifting to the northwest
by 18Z. Showers and thunderstorms developing in the vicinity of
the terminal this afternoon into this evening will likely produce
some periods of gusty and/or erratic winds. There is a 20 percent
chance of a thunderstorm directly impacting the terminal, most
likely between 23Z and 02Z.

Rest of Utah and southwest Wyoming...VFR conditions are expected
to prevail across the area through the valid TAF period. Showers
and thunderstorms will develop across the higher terrain this
afternoon, with some drift into the valleys possible late this
afternoon into the early evening. The most likely area for valley
convection is for areas north and east of the higher terrain, such
as the Uinta Basin and southwest Wyoming. Any storms that develop
will be capable of producing heavy rain that will result in
temporary MVFR/IFR conditions as well as frequent lightning and
gusty winds.

&&

.FIRE WEATHER...Monsoonal moisture remains in place across the
region, which will allow for scattered to numerous showers and
thunderstorms through Monday, primarily during the afternoon and
early evening. Convection today will be primarily focused over the
higher terrain with some drift into the valleys during the late
afternoon into the early evening. Sunday looks to be more active,
however, as a weak weather disturbance brushes by the area.With
abundant moisture in place any storms that form will be capable
of producing heavy rainfall. Temperatures will continue to run a
bit below normal, and relative humidity values will remain
elevated with good to excellent overnight recovery. As this
weather system passes moves east of the area, drier air will
spread across the region beginning Tuesday, lingering through
much of the upcoming week.

&&

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

Traphagan

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
541 AM MDT Sat Jul 31 2021

UTZ101>131-WYZ021-011200-
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-
541 AM MDT Sat Jul 31 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 and
gusty winds are expected this afternoon and evening. There is a
potential for localized flash flooding, especially in south
wester Utah and in prone areas such as slot canyons, burn scars,
areas of steep terrain, and normally dry washes and streams.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

The moist airmass will remain in place through Monday. Daily
showers and thunderstorms capable of heavy rain and gusty winds
will occur each afternoon and evening across much of the forecast
area. Drier air will move into the area beginning Tuesday, and
remain in place through the remainder of the 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

Special Weather Statement
National Weather Service Salt Lake City UT
1231 PM MDT Sat Jul 31 2021

UTZ112-WYZ021-311915-
Western Uinta Mountains UT-Southwest Wyoming WY-
1231 PM MDT Sat Jul 31 2021

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL SUMMIT AND SOUTHWESTERN
UINTA COUNTIES UNTIL 115 PM MDT...

At 1230 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm 14 miles north of Mirror Lake, or 24 miles south
of Evanston...moving north at 5 mph.

Half inch hail will be possible.

This storm will remain over mainly rural areas of central Summit and
southwestern Uinta Counties.

This includes Mirror Lake Highway between mile markers 47 and 54.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4085 11086 4088 11102 4108 11097 4101 11074
TIME...MOT...LOC 1830Z 200DEG 5KT 4091 11091

ND

Special Weather Statement
National Weather Service Salt Lake City UT
112 PM MDT Sat Jul 31 2021

UTZ122-125-311945-
Southwest Utah UT-Southern Mountains UT-
112 PM MDT Sat Jul 31 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL WASHINGTON AND
SOUTHWESTERN IRON COUNTIES UNTIL 145 PM MDT...

At 111 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm 21 miles northeast of Beaver Dam...moving west at
15 mph.

Penny size hail will be possible.

Locations impacted include...
Modena.

This includes the following highways...
 Utah Route 18 between mile markers 42 and 51.
 Utah Route 56 between mile markers 10 and 28.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

This storm may intensify, so be certain to monitor local radio and
available television stations for additional information and possible
warnings from the National Weather Service.

&&

LAT...LON 3772 11358 3758 11364 3760 11397 3784 11390
TIME...MOT...LOC 1911Z 104DEG 12KT 3767 11371

ND

Special Weather Statement
National Weather Service Salt Lake City UT
139 PM MDT Sat Jul 31 2021

UTZ108-110>112-312015-
Wasatch Back UT-Western Uinta Mountains UT-Wasatch Mountains I-
80 North UT-Wasatch Mountains South of I-80 UT-
139 PM MDT Sat Jul 31 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN SALT LAKE...
SOUTHEASTERN MORGAN AND WEST CENTRAL SUMMIT COUNTIES UNTIL 215 PM
MDT...

At 138 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm over East Canyon State Park, or 8 miles west of
Coalville...moving north at 25 mph.

Penny size hail will be possible.

Locations impacted include...
Park City, Morgan, Coalville, Summit Park, East Canyon State Park,
South Snyderville Basin, North Snyderville Basin, Mill Creek Canyon,
Henefer, Echo, Parleys Summit, Echo Reservoir, Snyderville, Kimball
Junction, Croydon and Portersville.

This includes the following highways...
 Interstate 84 between mile markers 103 and 119.
 Interstate 80 in Utah between mile markers 137 and 154, and between
mile markers 161 and 173.
 US Route 40 between mile markers 0 and 4.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

This storm may intensify, so be certain to monitor local radio and
available television stations for additional information and possible
warnings from the National Weather Service.

If on or near East Canyon or Echo Reservoirs, get out of the water
and move indoors or inside a vehicle. Remember, lightning can strike
out to 10 miles from the parent thunderstorm. If you can hear
thunder, you are close enough to be struck by lightning. Move to
safe shelter now! Do not be caught on the water in a thunderstorm.

&&

LAT...LON 4067 11145 4068 11166 4114 11169 4111 11133
TIME...MOT...LOC 1938Z 185DEG 20KT 4087 11155

ND