Special Weather Statement, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
216 PM MST Tue Jul 11 2017

.SYNOPSIS...
Near normal temperatures are expected through the week as high
pressure remains positioned over the Great Basin. Thunderstorms will
be possible over the higher terrain and parts of the lower deserts
of south-central and southwest Arizona each day. Areas of blowing
dust and strong winds will likely accompany any thunderstorms that
develop.

&&

.DISCUSSION...

An extensive area of high and midlevel clouds are over the
eastern half of our CWA this afternoon which has limited surface
warming so far today. As of noon, temperatures are anywhere from
4-8 degrees cooler than they were at this time yesterday although
areas further west, like Blythe and El Centro, are nearly similar
under mostly sunny skies. Despite the cloud cover, convection is
already firing up on the rim this afternoon while further south
near Tucson, convection has been slow to develop as temperatures
are running excessively cooler (-15F) today from last nights rain.

The 12Z sounding from this morning shows that PWs are up to 1.8
inches in Phoenix, up 0.2 inches from 24 hours ago while there was
very little 0-6km shear (~10 kts). According to the SPC
climatology page, developed by one of our very own local
forecasters, PWs were near record climatology levels this morning
which will favor heavy rains over strong downburst winds this
afternoon. However, localized downburst gusts as we saw yesterday
are certainly not out of the question.

The latest HRRR simulation continues to shows an outflow boundary
moving through the Phoenix area between 3-6Z tonight. This
boundary, if it does form, will likely approach out of the
northeast as most of today's convection is centered along the
rim. The big question is whether or not this outflow will be
strong enough to initiate convection again in the Phoenix area.
Local research has shown that PWs above 1.5 inches do not
necessarily translate to more severe thunderstorms warnings nor
area lightning coverage in our CWA. With that said, forcing is
likely more important when we get this saturated so a strong
outflow boundary will be needed to generate activity in the valley
tonight. Most CAMs do show some sort of boundary moving though
Phoenix, although chances of initiating convection at a particular
point remains between 10-20%.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:

Winds will remain out of the west with some gusts up to 15 to 20 kts
through around 03Z. Thunderstorms will continue to develop across
the higher terrain north, east, and southeast of Phoenix terminals
this afternoon, with a likely chance that an outflow from the east
to northeast could affect terminals later this afternoon into early
this evening (around 03Z). This in term would change the wind flow
to an easterly to northeasterly direction. There is also the
possibility for new storm development along this outflow boundary.
However, there's higher confidence on the outflow boundary than
actual storms over the terminals, but the possibility is there and
deserves mention in the discussion. The northeasterly wind shift
from the outflow is reflected in the 18Z TAFS, but should be taken
with caution due to lower confidence in the exact temporal and areal
coverage. SCT-BKN mid-high cloud layers mainly aoa 10k feet to
prevail through the taf period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Rather dry airmass will keep cloud cover reduced to just FEW to SCT
mid- and high- level cloud layers through the taf period. Winds to
mainly follow typical diurnal trends at KIPL. Winds to remain mainly
southerly at KBLH with a few afternoon gusts up to 20 kts.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Thursday through Monday:

A gradual increase in available moisture levels to result in an
increase in humidities and monsoon thunderstorm activity through the
period. Thunderstorm coverage to rise from isolated-scattered on
Thursday to scattered-numerous by Sunday/Monday. Locally heavy rains
are possible by Sunday/Monday, especially over the higher terrain
north and east of Phoenix. Temperatures to fall from slightly above
normal levels on Thursday to near, or slightly below normal by
Sunday/Monday. Minimum humidities to rise from the 15-30 percent
range on Thursday into the 25-40 percent range by Sunday/Monday,
with good-excellent overnight recoveries.

&&

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

&&

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

Visit us on Facebook, Twitter, and at weather.gov/phoenix

DISCUSSION...Wilson
AVIATION...Hernandez
FIRE WEATHER...Percha

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Special Weather Statement
National Weather Service Phoenix AZ
433 PM MST TUE JUL 11 2017

AZZ560-562-563-120015-
Southeast Gila County AZ-San Carlos AZ-Globe/Miami AZ-
433 PM MST TUE JUL 11 2017

...SIGNIFICANT WEATHER ADVISORY FOR GILA COUNTY UNTIL 515 PM MST...

At 432 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from 17 miles northwest of Hilltop to 12 miles north
of Cutter. Movement was northwest at 10 mph.

Winds in excess of 40 mph will be possible with these storms.

These storms will remain over mainly rural areas of Gila County.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy 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.

&&

LAT...LON 3384 11055 3343 11053 3346 11082 3368 11085
      3368 11083 3366 11078 3379 11068 3385 11056
TIME...MOT...LOC 2332Z 113DEG 9KT 3382 11062 3352 11060

CK

Special Weather Statement
National Weather Service Phoenix AZ
602 PM MST TUE JUL 11 2017

AZZ556-558-562-563-120145-
Southeast Gila County AZ-Tonto Basin AZ-Globe/Miami AZ-
Pinal/Superstition Mountains AZ-
602 PM MST TUE JUL 11 2017

...SIGNIFICANT WEATHER ADVISORY FOR GILA...MARICOPA AND PINAL
COUNTIES UNTIL 645 PM MST...

At 602 PM MST, Doppler radar was tracking a strong thunderstorm near
Tonto National Monument, or 7 miles southeast of Roosevelt, moving
southeast at 10 mph.

Wind gusts up to 50 mph will be possible with this storm.

This storm will remain over mainly rural areas of Gila...Maricopa and
Pinal Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

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

&&

LAT...LON 3361 11116 3370 11097 3353 11082 3343 11107
TIME...MOT...LOC 0102Z 331DEG 8KT 3360 11103

CK