Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
406 AM MDT Sun Jul 18 2021

.SYNOPSIS...High pressure will remain across the region for much
of the next week. Monsoonal moisture will begin to increase
across southern Utah today, then spread across the remainder of
the area and remain in place through the rest of the week.

&&

.SHORT TERM (Through 12Z Wednesday)...Another day under a broad
upper level ridge across the Interior West is in store for Utah to
end this mid-July weekend. The edge of the next moisture surge is
quite apparent on satellite imagery early this morning, with
several additional shortwaves noted across Arizona. While the best
forcing for showers this morning will push west of the area, a few
isolated showers will be possible across far southern Utah through
mid-morning.

Expect precipitable water values across southern Utah to gradually
increase, shifting to ~150% of normal by this afternoon. The
previously mentioned moisture gradient/embedded shortwave should
serve as a trigger point for convection across southwestern Utah
this afternoon. SBCAPE values near 500-1000 J/kg can be expected
across this area...with deep layer shear between 10-20 kts. Most
CAM guidance focuses development across southwestern Utah during
the afternoon...with convection hugging the Utah/Nevada border for
much of the overnight hours in response to the gradual northward
progression of the previously mentioned wave.

Sunday will be a hot day across northern Utah...with temperatures
approaching 100F for the northern valleys. Given how hot this
summer has already been...this is more of a broken record than
anything noteworthy for most individuals in these areas.

As the Sunday convection gradually diminishes early Monday
morning, another round of convection is expected Monday afternoon
into Monday night. There will be two primary forcing
mechanisms...one shifting northward from Arizona and another the
result of an embedded wave shifting northeastward across northern
Nevada. While HREF ensemble mean SBCAPE values are nothing to
write home about (averaging around 500-750 J/kg across the state),
deep layer shear will be near 20-25 kts across northern Utah
Monday afternoon and evening.

As a result of these two primary areas of forcing, CAMS are
largely focusing convection across southern Utah, moving northward
with the southern wave...with another round of convection
shifting northeastward into northern Utah Monday evening into
Monday night. With precipitable water values in the 150-200+% of
normal range, this has the potential to bring a soaking rain to
portions of Utah. As is typical, timing shortwaves this far out is
wrought with potential issues...but this is something to watch
for future shifts.

By Tuesday, the ridge shifts subtly south and east in response to
a shift in the upper trough near the Pacific Coast. The net result
from this will likely be drier air shifting into northwestern
Utah...suppressing convection across much of northern and
potentially western Utah. Monsoon moisture will remain across much
of eastern and southern Utah...with another round of convection
expected Tuesday afternoon and evening.

As far as flash flood potential...expect southwestern Utah to see
thunderstorms with potentially heavy rain this afternoon and
evening. This threat will likely shift to much of the state
Monday. Those with outdoor plans in southern Utah should monitor
forecasts and have a "plan B" if weather does not cooperate. Those
near recent burn scars should continue to monitor forecasts and
watch for future watches/warnings.

.LONG TERM (After 12Z Wednesday)...The ridge will remain in place
into the extended forecast. Ensemble guidance has good agreement
in a weak trough moving eastward from the Pacific coast into
Canada and some flattening of the ridge, but not enough to have a
noticeable effect on weather conditions locally. Monsoon moisture
will keep building in from the south with the ridge centered near
the Colorado/Utah border. Precipitable water values upwards of 1"
are expected in southern Utah. Values around 1" are expected in
the north. Flash flooding will remain a threat with these
thunderstorms.

Ensemble solutions diverge later in the week. Nearly 3/4ths of
EPS members retrograde the ridge westward, centering it over
Nevada, resulting in drier conditions. A small percentage of CMCE
and GEFS members also do that. The majority support the ridge
staying nearly stationary or push it eastward. That solution is
slightly more likely if you consider all members from the
aforementioned ensemble guidance. If it plays out, shower and
thunderstorms chances will last into the following week. If the
solution largely influenced by the EPS does, drier conditions
would be expected around Friday.

&&

.AVIATION...KSLC...VFR conditions are expected through the valid
TAF period. Southeast winds will transition to the northwest
around 19Z. Scattered mid to high clouds are expected with dry
conditions. Isolated to scattered thunderstorms will build into
northern Utah in the evening, but the dry environment will result
in gusty outflow winds being possible after 00Z.

Rest of Utah and southwest Wyoming...VFR conditions are expected
through the valid TAF period. Scattered showers and thunderstorms
will start in the early afternoon in southern Utah. Showers and
thunderstorms will build northward, but drier conditions will
result in better chances for gusty outflow winds later in the
afternoon into the evening. Thunderstorms will diminish after
03Z, but isolated to scattered rain showers will still be possible
in southern Utah.

&&

.FIRE WEATHER...High pressure will remain centered across the Four
Corners region for much of the next week. As Utah remains on the
west side of this high pressure, this will help to draw monsoonal
moisture northward into the state for much of the week. Expect the
first round of thunderstorms with wetting rain potential across
southern Utah today, spreading north and east Monday. Any
thunderstorms over the northern half of Utah will trend toward the
dry side and may contain gusty and erratic winds. By Monday, most
storms across the state will largely trend toward the wetter
side.

&&

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

Hazardous Weather Outlook
National Weather Service Salt Lake City UT
316 AM MDT Sun Jul 18 2021

UTZ101>131-WYZ021-190930-
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-
316 AM MDT Sun Jul 18 2021

This Hazardous Weather Outlook is for portions of central Utah...
northern Utah...southern Utah...southwest Utah and southwest
Wyoming.

.DAY ONE...Today and Tonight

Showers and thunderstorms will develop across the higher terrain
of Utah this afternoon and evening. Any showers and thunderstorms
will be capable of gusty and erratic winds. Thunderstorms across
southern Utah will be capable of heavy rain.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Monsoonal moisture will remain across the region through most of
the next week. Showers and thunderstorms will be capable of heavy
rain, gusty winds and small hail each afternoon and evening. Those
planning outdoor activities especially across particularly flood
prone areas of southern Utah should continue to monitor future
forecasts.

.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
312 PM MDT Sun Jul 18 2021

UTZ122-125-182200-
Southwest Utah UT-Southern Mountains UT-
312 PM MDT Sun Jul 18 2021

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN BEAVER COUNTY UNTIL 400
PM MDT...

At 312 PM MDT, National Weather Service Doppler radar indicated a
strong thunderstorm 11 miles east of Milford...moving west at 10 mph.

Wind gusts up to 50 mph will be possible.

Locations impacted include...
Milford, Minersville and Adamsville.

This includes Utah Route 21 between mile markers 74 and 103.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3856 11276 3815 11269 3815 11298 3851 11310
TIME...MOT...LOC 2112Z 070DEG 7KT 3845 11282

Woodward