Dust Storm Warning 24, 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
1005 PM MST Fri Aug 13 2021

AZZ546>551-553-555-558-140545-
South Mountain/Ahwatukee AZ-Fountain Hills/East Mesa AZ-
Scottsdale/Paradise Valley AZ-Northwest Pinal County AZ-
East Valley AZ-Southeast Valley/Queen Creek AZ-
Apache Junction/Gold Canyon AZ-Rio Verde/Salt River AZ-
Pinal/Superstition Mountains AZ-
1005 PM MST Fri Aug 13 2021

...Strong thunderstorms will impact portions of Maricopa and Pinal
Counties through 1045 PM MST...

At 1004 PM MST, Doppler radar was tracking strong outflow boundary
along a line extending from Downtown Mesa to near Phoenix Mesa
Gateway Airport to near Apache Junction. Movement was south at 15
mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

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

Locations impacted include...
Mesa, Chandler, Gilbert, Tempe, Apache Junction, Gold Canyon, Sun
Lakes, East Mesa, Queen Creek, Tempe Marketplace, Papago Park, Gold
Camp, Falcon Field Airport, Salt River Indian Community, Lost
Dutchman State Park, Goldfield, Usery Mountain Park, San Tan Village
Mall, San Tan Valley and Seville.

This includes the following highways...
AZ Interstate 10 between mile markers 154 and 175.
US Highway 60 between mile markers 173 and 211.
AZ Route 87 between mile markers 148 and 180.

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 and southeastern Arizona.

&&

LAT...LON 3313 11131 3306 11164 3316 11199 3350 11197
      3348 11168 3349 11142
TIME...MOT...LOC 0504Z 354DEG 14KT 3341 11184 3334 11168 3339 11151

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

SDB

Special Weather Statement
National Weather Service Phoenix AZ
1011 PM MST Fri Aug 13 2021

AZZ534-537-538-540>544-546-548-550-551-553-554-559-140600-
Sonoran Desert Natl Monument AZ-Aguila Valley AZ-
Cave Creek/New River AZ-Northwest Pinal County AZ-East Valley AZ-
Tonopah Desert AZ-Southeast Valley/Queen Creek AZ-
West Pinal County AZ-North Phoenix/Glendale AZ-
South Mountain/Ahwatukee AZ-Scottsdale/Paradise Valley AZ-
Buckeye/Avondale AZ-Central Phoenix AZ-Deer Valley AZ-
Northwest Valley AZ-
1011 PM MST Fri Aug 13 2021

...Strong thunderstorms will impact portions of Maricopa and Pinal
Counties through 1100 PM MST...

At 1010 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from near Wittmann to near Sun City to Metro Center
Mall. Movement was west at 10 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

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

Locations impacted include...
Phoenix, Chandler, Glendale, Tempe, Peoria, Surprise, Avondale,
Goodyear, Buckeye, El Mirage, Paradise Valley, Tolleson, Youngtown,
Waddell, Laveen, Cashion, Sun City, Wittmann, Sun City West and
Litchfield Park.

This includes the following highways...
AZ Interstate 10 between mile markers 107 and 164.
AZ Interstate 17 between mile markers 195 and 226.
AZ Route 51 between mile markers 1 and 13.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms 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 southeastern Arizona.

&&

LAT...LON 3373 11296 3336 11266 3314 11220 3312 11199
      3340 11190 3383 11209 3383 11242
TIME...MOT...LOC 0510Z 074DEG 7KT 3377 11244 3365 11228 3357 11211

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

SDB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1015 PM MST FRI AUG 13 2021

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

1013 PM     HEAVY RAIN       6 ESE DEER VALLEY       33.65N 112.01W
08/13/2021  M0.63 INCH       MARICOPA           AZ   TRAINED SPOTTER

            MEASURED IN 11 MINUTES.

&&

PI

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1034 PM MST FRI AUG 13 2021

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

1023 PM     FLASH FLOOD      3 S DEER VALLEY         33.63N 112.12W
08/13/2021                   MARICOPA           AZ   TRAINED SPOTTER

            FLOODING ON INTERSTATE 17 AT GREENWAY.

&&

PI

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1050 PM MST FRI AUG 13 2021

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

0950 PM     DUST STORM       2 SSW WITTMANN          33.75N 112.55W
08/13/2021                   MARICOPA           AZ   TRAINED SPOTTER

            LESS THAN ONE QUARTER MILE VISIBILITY.

0955 PM     TSTM WND GST     2 SSW WITTMANN          33.75N 112.55W
08/13/2021  E60 MPH          MARICOPA           AZ   TRAINED SPOTTER

            60 MPH GUST MEASURED FROM HOME WEATHER
            STATION.

1027 PM     HEAVY RAIN       5 E DEER VALLEY         33.65N 112.03W
08/13/2021  M1.10 INCH       MARICOPA           AZ   TRAINED SPOTTER

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1051 PM MST FRI AUG 13 2021

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

0943 PM     TSTM WND DMG     3 WSW FOUNTAIN HILLS    33.59N 111.80W
08/13/2021                   MARICOPA           AZ   PUBLIC

            THUNDERSTORM WIND GUSTS ESTIMATED BETWEEN
            50MPH AND 60MPH. TREE BRANCHES DOWN IN AREA.

&&

JR