Severe Thunderstorm Warning 61, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
727 PM MST Fri Aug 13 2021

.UPDATE...Updated short-term discussion for convective trends.

&&

.SYNOPSIS...
High levels of moisture will remain entrenched across the region
into early next week, leading to persistent chances for showers
and thunderstorms. The primary threats with any storms remain
localized heavy rainfall that may cause flash flooding. A Flash
Flood Watch is in effect for south-central Arizona through Sunday
afternoon. Strong winds and some blowing dust will also be
possible for desert locations. With increased cloud cover and
showers, temperatures will remain near to below normal.

&&

.DISCUSSION...
A Severe Thunderstorm Watch has been issued until 3 AM PDT/MST for
most of south-central and southwest Arizona. The 00Z sounding from
Phoenix sampled a very unstable air mass (near 1800 J/kg of
MLCAPE) with 20 kt of ENE mid-level flow in place. Earlier
convection over southern Gila County promptly weakened as it moved
off the higher terrain, likely a result of inhibition in place
over the lower deserts. However, an upper impulse is contributing
to an organized line of convection developing across Gila County
this evening. This area of convection should provide the necessary
forcing for ascent to overcome the weak capping inversion in
place, and realize the very unstable air mass in place. Expecting
primarily a wind threat with more linear storm structures, though
hail will certainly be a possibility with more isolated storms as
well. There is a signal that a quasi-organized convective line
will persist overnight into southwest Arizona and approach the
lower Colorado River Valley Saturday morning.

.PREVIOUS DISCUSSION...

After an active Friday night, Saturday would typically be thought
to be a "down" day. That may not necessarily hold as the enhanced
northeasterly mid level flow remains in place and the pattern is
conducive to mountain-valley propagating storms. On Sunday, a mid
level front moving out of NM and into AZ may push enough
dry/capping air in from the Four Corners to pair the heavy rain
threat a bit but the increased dry air may lead to a higher wind
threat. Ultimately a similar pattern continues Monday and Tuesday,
before a broader realignment mid-week. Global ensembles are still
moving a trough through the Pacific Northwest starting Wednesday.
While a deep, closed trough is not favored by the majority of
members, we should see a mid/upper level southwest flow develop
which will begin shunting the moisture in place east. Many members
do generate additional around Wednesday, perhaps indicating there
will be shortwave energy that lifts through our area on the
increasing southerly flow. PoPs begin to trend down thereafter.

Across southwest Arizona, the potential for isolated
thunderstorms and decaying large outflows will continue most days.
Even a couple of desert mountain thunderstorms could develop
across southeast California any of the days given the humid
boundary layer.

With more sun, temperatures will remain fairly close if not a
little above normal across southeast California and near normal
toward Yuma. Further east, temperatures will remain below normal
for the Phoenix area. Thursday did briefly sneak up to 100F and
temperatures in the upper 90s to near 100 look to be common
through the next week.

&&

.AVIATION...Updated at 0001Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Normal diurnal wind trends are favored into the early evening hours.
Then good chances develop for storms to affect the area during the
mid-evening hours as storms from the east attempt to moving into the
Phoenix area. Current thinking (moderate confidence) is that
easterly outflows from strong storms near Globe will attempt to push
into the PHX area during the 0230Z-0300Z timeframe. There still is a
lesser confidence level as far as TS activity actually affecting the
terminals, thus leaving VCTS in the TAF's for now. CIGS will likely
drop into the 5-6k foot range.

Latest high-res model output is now beginning to converge on the
idea that convective activity could again develop over the PHX area
during the 06Z-10Z timeframe. Went ahead and included VCSH in the
TAF for that timeframe. Winds outside of the storms likely to remain
out of an easterly direction from mid-morning Sat, then gradually
shift to a southerly, then a southwesterly direction from the late
morning into the afternoon hours on Saturday. At this point, it
appears that there is much less chance for convective activity
Saturday afternoon/evening then what we are seeing today, thus have
left any mention of SHRA/TS out of the TAF's at this time. Outside
of storms expect BKN mid cloud CIGs of 10-15 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:

At KIPL, current light easterly winds to become westerly after 03Z,
with these winds continuing through the rest of the night. WInds at
KBLH to remain out of a southerly direction through most of tonight.
It now appears that chances of outflows from distant TS's to the
east are great enough to include a mention of a wind shift to
easterly at both SE CA TAF sites later tonight/early Sat. However,
storms chances at the terminals themselves are still quite low (20%
at KBLH and 5-10% at KIPL). During the day on Sat, expecting mainly
southerly winds at KBLH and SE-ly at KIPL.

&&

.FIRE WEATHER...
Sunday through Thursday:
Generally an active weather period will continue with persistent
chances for showers and thunderstorms, with the best chances
across southern Gila county decreasing as one goes west. Humidity
values themselves will remain quite elevated during this period,
with overnight values rising into the 50-90% range and daytime
values falling only 25-45% range. A modest drying trend may being
at the very end of the forecast period. Winds will favor typical
diurnal/terrain influences most days.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch through Sunday afternoon for AZZ534-537>563.

CA...None.
&&

DISCUSSION...Rogers
PREVIOUS DISCUSSION...Iniguez
AVIATION...Percha
FIRE WEATHER...Iniguez

Special Weather Statement
National Weather Service Phoenix AZ
414 PM MST Fri Aug 13 2021

AZZ558-560-562-563-140000-
Southeast Gila County AZ-San Carlos AZ-Globe/Miami AZ-
Pinal/Superstition Mountains AZ-
414 PM MST Fri Aug 13 2021

...A strong thunderstorm will impact portions of Gila County through
500 PM MST...

At 413 PM MST, Doppler radar was tracking a strong thunderstorm near
Cutter, or 8 miles east of Globe, moving west at 15 mph.

HAZARD...Wind gusts of 50 to 55 mph and nickel 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...
Globe, Miami, Cutter, Central Heights-Midland City, Claypool and
Inspiration.

This includes the following highways...
US Highway 60 between mile markers 241 and 263.
AZ Route 70 between mile markers 253 and 263.
AZ Route 77 between mile markers 162 and 170.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

&&

LAT...LON 3354 11057 3337 11052 3321 11086 3351 11097
TIME...MOT...LOC 2313Z 074DEG 12KT 3344 11065

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...55 MPH

SDB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
527 PM MST FRI AUG 13 2021

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

0510 PM     HEAVY RAIN       1 E CLAYPOOL            33.41N 110.82W
08/13/2021  M1.20 INCH       GILA               AZ   PUBLIC

&&

Special Weather Statement
National Weather Service Phoenix AZ
557 PM MST Fri Aug 13 2021

AZZ547-549-552-555-558-140145-
Fountain Hills/East Mesa AZ-Apache Junction/Gold Canyon AZ-
Superior AZ-Rio Verde/Salt River AZ-Pinal/Superstition Mountains AZ-
557 PM MST Fri Aug 13 2021

...A strong thunderstorm will impact portions of Maricopa and Pinal
Counties through 645 PM MST...

At 557 PM MST, Doppler radar was tracking a strong thunderstorm 7
miles south of Apache Lake, or 13 miles northeast of Gold Canyon,
moving west at 15 mph.

HAZARD...Winds in excess of 40 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...
Apache Junction, Gold Canyon, Florence Junction, Queen Valley, Canyon
Lake, Superstition Mountains, Gold Camp, Kings Ranch, Lost Dutchman
State Park, Goldfield and Tortilla Flat.

This includes the following highways...
US Highway 60 between mile markers 198 and 212.
AZ Route 79 near mile marker 150.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

&&

LAT...LON 3352 11115 3334 11116 3322 11140 3345 11158
      3360 11147
TIME...MOT...LOC 0057Z 092DEG 12KT 3347 11125

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

SDB

Special Weather Statement
National Weather Service Phoenix AZ
834 PM MST Fri Aug 13 2021

AZZ534-537-538-541-542-544-545-547-140415-
Aguila Valley AZ-New River Mesa AZ-Cave Creek/New River AZ-
Tonopah Desert AZ-Deer Valley AZ-Northwest Valley AZ-
Rio Verde/Salt River AZ-North Phoenix/Glendale AZ-
834 PM MST Fri Aug 13 2021

...Strong thunderstorms will impact portions of Maricopa County
through 915 PM MST...

At 833 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from near Black Canyon City to 8 miles southeast of
Rock Springs to near Camp Creek. Movement was southwest at 45 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Phoenix, Glendale, Scottsdale, Peoria, Surprise, El Mirage,
Youngtown, New River, Sun City West, Circle City, Sun City, Wittmann,
Cave Creek, Carefree, Deer Valley Airport, Downtown Peoria, Surprise
Stadium, Arrowhead Mall, Desert Mountain and Camp Creek.

This includes the following highways...
AZ Interstate 17 between mile markers 211 and 241.
US Highway 60 between mile markers 110 and 150.
AZ Route 101 between mile markers 11 and 28.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 300 AM MST for
south central Arizona.

&&

LAT...LON 3399 11161 3357 11216 3362 11262 3384 11278
      3399 11273 3389 11228 3391 11224 3395 11224
      3397 11219 3405 11215
TIME...MOT...LOC 0333Z 054DEG 41KT 3409 11208 3400 11201 3395 11183

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

SDB

Special Weather Statement
National Weather Service Phoenix AZ
858 PM MST Fri Aug 13 2021

AZZ547-556-557-140445-
Mazatzal Mountains AZ-Tonto Basin AZ-Rio Verde/Salt River AZ-
858 PM MST Fri Aug 13 2021

...A strong thunderstorm will impact portions of Gila and Maricopa
Counties through 945 PM MST...

At 857 PM MST, Doppler radar was tracking a strong thunderstorm over
Ballantine Trailhead, moving west at 10 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...
Round Valley, Ballantine Trailhead, Sugarloaf Mountain, Sunflower,
Punkin Center, Tonto Basin, Four Peaks and Rio Verde.

This includes the following highways...
AZ Route 87 between mile markers 201 and 219.
AZ Route 188 between mile markers 259 and 262.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

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

A Severe Thunderstorm Watch remains in effect until 300 AM MST for
south central and east central Arizona.

&&

LAT...LON 3387 11130 3367 11127 3363 11165 3364 11166
      3391 11166
TIME...MOT...LOC 0357Z 089DEG 7KT 3377 11145

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

SDB