Severe Thunderstorm Warning 8, NWS Phoenix, AZ

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
520 PM MST Tue Jul 23 2019

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
Expect storm development to continue over higher terrain
locations this afternoon, with activity gradually spreading into
the lower deserts. Locally heavy rain and areas of blowing dust
are possible. A Flash Flood Watch is in effect from 3 PM till
midnight for Maricopa, Pinal, and southern Gila county. High
pressure will slowly become centered over Arizona for a downtrend
in storm chances starting Wednesday. High temperatures will also
increase...especially during the latter half of the week.

&&

.DISCUSSION...
High pressure is centered over northwest Utah, with
east/southeasterly flow over the region. Moisture values are
exceptionally high, with Phoenix's PWATs above the 90th percent
moving average. Earlier today, we were really relying on cloud
cover to thin out to maximize daytime heating and instability,
especially over the lower deserts. Phoenix's convective
temperature today was 105 degrees, and since clouds eventually
did thin out, we've had no trouble warming up to 107 degrees and
we could possibly warm up a little more. With the high being
further north today, it's been evident, even by looking at
aircraft sounding, that mid-level temperatures have cooled off a
bit, which will also aid in storm development today. As a result,
we currently see thunderstorms favoring the high terrain in south-
central Arizona and even in southeast California. We can expect
this coverage to continue to fill in today and tonight, and
possibly even continue into the early morning hours tomorrow
(primarily across southwest Arizona and southeast California early
tomorrow morning). With significant moisture in place, and very
slow storm motion, flooding will be the biggest impact today. Thus
we have issued a Flash Flood Watch for Maricopa, southern Gila,
and Pinal county from 3 PM till midnight tonight. The Flash Flood
Watch may be expanded westward if warranted.

Wednesday through Monday...
There is general model agreement that the storm activity over the
lower deserts trends down beginning Wednesday. This is due in large
part to an increase in stability caused by the the high becoming
centered over Arizona. That also decreases steering flow which
makes it harder for storms to advect from higher terrain. There
also looks to be a west to east decline of moisture with time. The
moisture doesn't drop to nothing. In fact, 1000-700mb mean mixing
ratios don't drop dramatically over most of Arizona. Thus, there
will still be higher terrain storms (mainly outside of our CWA).
With less storms and clouds, and the location of the high, max
temps will climb. At this time, it looks like we will remain below
Excessive Heat thresholds. Over the weekend, there are some
indications that the high center may shift westward a little bit
which would make for somewhat more favorable steering flow. It
remains to be seen. For now, have temps trending closer to normal
with "low grade" monsoon PoPs.

&&

.AVIATION...Updated at 0520 UTC

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

Potential continues for another round of gusty easterly outflow
winds into the greater Phoenix area this evening. For now,
atmosphere seems a bit less unstable as compared to yesterday and
thunderstorms east/southeast of Phoenix have been slower to develop.
Still, for now we will continue to call for east/southeast winds up
to 25kt to move in by 03z-04z for the TAF sites. Confidence is not
as high as yesterday for either timing or strength of the winds.

Otherwise, look for isolated showers or storms to accompany, or
develop slightly after, the main outflows move in. After 06z tonight
will continue with -SHRA through much of the night, as considerable
mid/high cloud will overspread the area in association with a weak
disturbance rotating around the high. Look for BKN-OVC decks aoa 10k
feet after 06z tonight. Clearing to occur during the morning hours
with SCT-BKN mid and high decks lingering into the afternoon.
Chances for storms are there for Wednesday late afternoon or evening
but they will likely be more isolated and confidence in their
occurrence or timing is too low to mention in the TAFs for now.

Southeast California/Southwest Arizona including KIPL and KBLH:

Isolated convection will occur over the western deserts this evening
but due to low areal coverage, confidence too low to mention thunder
in the TAF sites. Will just go with SCT-BKN decks 8-12k feet and BKN-
OVC mid/high level decks overnight into the day on Wednesday. Winds
will favor the south next 24 hours at KBLH, and favor the southeast
at KIPL. Winds this evening may initially favor the west before
turning to the southeast later tonight. Speeds mostly less than
12kt.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday:
Expect thunderstorms to be limited to the higher terrain of south-
central AZ. Max temperatures will climb to several degrees above
normal Friday and Saturday before beginning to trend down. Any
thunderstorms that manage to form will be very effective at
producing strong winds but with little wetting rain. With the
rising temperatures, minimum humidities decline as well but are
expected to remain well into the teens. Overnight recovery
declines some but remains at least fair (better over higher
terrain).

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch until midnight MST tonight for AZZ534-537>563.

CA...None.
&&

DISCUSSION...Hernandez/AJ
AVIATION...CB
FIRE WEATHER...AJ

Special Weather Statement
National Weather Service Phoenix AZ
445 PM PDT Tue Jul 23 2019

CAZ564-565-569-240030-
Chuckwalla Mountains CA-Imperial County Southeast CA-
Palo Verde Valley CA-
445 PM PDT Tue Jul 23 2019

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN IMPERIAL COUNTY UNTIL 530
PM PDT...

At 445 PM PDT, Doppler radar was tracking a strong thunderstorm 19
miles north of Algodones Dunes, or 23 miles west of Martinez Lake,
moving south at 5 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Algodones Dunes.

This includes the following highways...
CA Interstate 8 between mile markers 70 and 71, and between mile
markers 80 and 85.
CA Route 78 between mile markers 42 and 66.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3324 11510 3330 11482 3280 11462 3270 11503
TIME...MOT...LOC 2345Z 351DEG 5KT 3301 11487

AD

Special Weather Statement
National Weather Service Phoenix AZ
450 PM MST Tue Jul 23 2019

AZZ548-549-551-553-555-240015-
Fountain Hills/East Mesa AZ-Northwest Pinal County AZ-East Valley AZ-
Southeast Valley/Queen Creek AZ-Apache Junction/Gold Canyon AZ-
450 PM MST Tue Jul 23 2019

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

At 449 PM MST, Doppler radar was tracking a strong thunderstorm near
Gold Canyon, moving northwest at 15 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Mesa, Apache Junction, Gold Canyon, Queen Creek, Gold Camp and
Phoenix Mesa Gateway Airport.

This includes the following highways...
US Highway 60 between mile markers 192 and 209.
AZ Route 202 between mile markers 32 and 35.

LAT...LON 3333 11136 3323 11139 3325 11169 3349 11160
TIME...MOT...LOC 2349Z 115DEG 14KT 3331 11144

SDB

Special Weather Statement
National Weather Service Phoenix AZ
505 PM MST Tue Jul 23 2019

AZZ558-560-562-563-240045-
Southeast Gila County AZ-San Carlos AZ-Globe/Miami AZ-
Pinal/Superstition Mountains AZ-
505 PM MST Tue Jul 23 2019

...SIGNIFICANT WEATHER ADVISORY FOR GILA COUNTY UNTIL 545 PM MST...

At 504 PM MST, Doppler radar was tracking a strong thunderstorm over
Globe. This storm was nearly stationary.

Pea size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Globe, Miami, Central Heights-Midland City, Claypool and Inspiration.

This includes the following highways...
US Highway 60 between mile markers 243 and 262.
AZ Route 70 between mile markers 253 and 258.
AZ Route 77 between mile markers 165 and 170.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3339 11063 3327 11074 3341 11093 3356 11076
      3348 11065
TIME...MOT...LOC 0004Z 134DEG 3KT 3338 11074

SDB

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