Special Weather Statement, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
935 PM MST Fri Aug 4 2017

.SYNOPSIS...
Thunderstorm chances will rapidly dwindle through the weekend and
into early next week as dry air spreads into the region. Any
rainfall will be relegated mainly to high terrain locations through
the middle of next week. As the atmosphere dries, temperatures will
also rebound towards near and slightly above average readings.

&&

.DISCUSSION...
Coverage of showers and storms were generally isolated this
afternoon and evening, with the strongest storms observed across
southeastern California and southwestern Arizona. A few cells
persist this evening across southern Maricopa and western Pinal
Counties.

Latest PSR sounding shows westerly flow through the troposphere
with significant drying noted (PWAT of 1.3 inches down from 1.71
inches this morning). Convective parameters from the latest
mesoanalysis suggest that activity will dissipate over the next
hour or two, given the presence of CIN and decreasing CAPE.
Nevertheless, some stronger returns are evident on radar and the
cells bear watching.

&&

.PREVIOUS DISCUSSION...
A deeper SW flow should develop this evening and into tomorrow
and will act to gradually dry the boundary layer through this
weekend. As such, convective activity will be minimal tomorrow
with only elevated portions of eastern Gila County seeing a shot
at storms. With even drier conditions forecast for the latter half
of the weekend, our entire CWA should remain dry on Sunday under
mostly sunny skies.

This drier synoptic pattern should hold into at least Tuesday as the
entire flow configuration upstream and north of the region will stay
blocked. In fact, it could be until the end of next week before
moisture seeps back into the region and the stronger deep westerly
flow relinquishes it influence. In the meantime, there is excellent
operational and ensemble support that central H5 heights near 594dm
will build into SE Arizona during the first half of next week. With
the drier airmass, these heights aloft would result in temperatures
rebounding back into a normal or slightly above normal range.
Certainly looking like nothing record breaking or excessive, but a
distinct change from the cooler more humid conditions of late.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Isolated storms will generally slide well south of the Phoenix
area this evening. However, there is a slight chance of a
thunderstorm through midnight, particularly at KPHX and KIWA.
Thunderstorms will generally remain relegated to the higher
terrain well north and east of Phoenix Saturday as drier air moves
into the region.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather impacts anticipated. Winds will follow typical
diurnal patterns.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday: Dry conditions prevail through Tuesday with
minimum humidities in the teens on the lower deserts. Overnight
humidities decline but remain good. Max temperatures increase
somewhat but only slightly above normal values. Storm chances return
to the higher terrain of south-central Arizona Wednesday and
Thursday humidities begin a modest upward trend during this time.
Winds next week will follow familiar warm season patterns.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

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DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Wilson/MO
AVIATION...Hirsch
FIRE WEATHER...AJ

Special Weather Statement
National Weather Service Phoenix AZ
950 PM MST FRI AUG 4 2017

AZZ548-550>555-050545-
South Mountain/Ahwatukee AZ-Northwest Pinal County AZ-East Valley AZ-
Southeast Valley/Queen Creek AZ-Apache Junction/Gold Canyon AZ-
Superior AZ-West Pinal County AZ-
950 PM MST FRI AUG 4 2017

...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA AND PINAL COUNTIES UNTIL
1045 PM MST/1045 PM PDT/...

At 947 PM MST, Doppler radar was tracking an area of thunderstorms
and associated outflow winds moving through Pinal County. Trained
weather spotters have reported low visibility in dust with the
outflow winds and running of washes in the area. Storms were moving
east at 10 mph.

Winds in excess of 40 mph, reduced visibility in blowing dust and
moderate to heavy rain will be possible with these storms.

Locations impacted include...
Mesa, Chandler, Gilbert, Casa Grande, Florence, Coolidge, Sun Lakes,
Queen Creek, Arizona City, La Palma, San Tan Village Mall, San Tan
Valley, Seville, Florence Junction, Bapchule, Olberg, Arizola,
Phoenix Mesa Gateway Airport, San Tan Mountain Park and Randolph.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Locally dense blowing dust is possible.  If you encounter blowing
dust while driving, pull over as far off the roadway as possible and
park. Turn off your headlights and keep your foot off the brake.

&&

LAT...LON 3276 11174 3276 11177 3280 11178 3276 11199
      3330 11198 3334 11143 3328 11124 3305 11122
      3290 11145 3273 11167 3273 11174
TIME...MOT...LOC 0447Z 257DEG 11KT 3307 11160

Nolte

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1025 PM MST FRI AUG 4 2017

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

0937 PM     DUST STORM       11 SE AK-CHIN VILLAGE   32.94N 111.93W
08/04/2017                   PINAL              AZ   TRAINED SPOTTER

            REPORT OF VSBY LESS THAN ONE-QUARTER MILE IN
            DUST FOR BRIEF TIME. ALSO PASSED ALONG
            DAMAGE TO A TRAILER IN THE HIDDEN VALLEY
            AREA (SW OF MARICOPA), KNOCKED OFF ITS BASE.
            WASHES IN THE AREA WERE RUNNING.

&&

Special Weather Statement
National Weather Service Phoenix AZ
1058 PM MST FRI AUG 4 2017

AZZ551>553-555-558-050645-
Northwest Pinal County AZ-Southeast Valley/Queen Creek AZ-
Apache Junction/Gold Canyon AZ-Superior AZ-
Pinal/Superstition Mountains AZ-
1058 PM MST FRI AUG 4 2017

...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA AND PINAL COUNTIES UNTIL
1145 PM MST...

At 1055 PM MST, Doppler radar was tracking an area of strong
thunderstorms near Randolph and Casa Grande, moving east at 15 mph.

Wind gusts up to 50 mph, reduced visibilities in blowing dust and
periods of moderate to heavy rainfall will be possible with these
storms. Outflow winds ahead of these storms will also continue to
track across northern Pinal County and portions of the far southeast
Phoenix Metro, dropping nighttime visibilities in dust and haze with
wind gusts 25 to 35 mph.

Locations impacted include...
Casa Grande, Apache Junction, Florence, Coolidge, Superior, Queen
Creek, La Palma, Blackwater, Chandler Heights, Magma, San Tan Valley,
Coolidge Airport, Florence Junction, Queen Valley, Olberg, Arizola,
Boyce Thompson Arboretum, San Tan Mountain Park, Randolph and Gold
Camp.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Locally dense blowing dust is possible.  If you encounter blowing
dust while driving, pull over as far off the roadway as possible and
park. Turn off your headlights and keep your foot off the brake.

&&

LAT...LON 3276 11174 3276 11177 3280 11178 3279 11188
      3301 11196 3337 11152 3336 11148 3338 11124
      3324 11096 3310 11115 3273 11173
TIME...MOT...LOC 0555Z 255DEG 12KT 3292 11161

JN