Severe Thunderstorm Warning 56, NWS Phoenix, AZ

372 
WWUS55 KPSR 130514
SVSPSR

Severe Weather Statement
National Weather Service Phoenix AZ
1014 PM MST SAT AUG 12 2017

AZC013-130545-
/O.CON.KPSR.SV.W.0056.000000T0000Z-170813T0545Z/
Maricopa AZ-
1014 PM MST SAT AUG 12 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1045 PM MST
FOR MARICOPA COUNTY...

At 1014 PM MST, a severe thunderstorm was located over Camelback
Ranch, or near Youngtown, moving northeast at 15 mph.

HAZARD...60 mph wind gusts. 

SOURCE...Radar indicated. 

IMPACT...Expect damage to roofs, siding, and trees. 

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

Continuous cloud to ground lightning is occurring with this storm.
Move indoors immediately. Lightning is one of nature's leading
killers. Remember, if you can hear thunder, you are close enough to
be struck by lightning.

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

&&

LAT...LON 3333 11240 3356 11267 3373 11242 3342 11210
TIME...MOT...LOC 0514Z 226DEG 12KT 3353 11233 

HAIL...<.75IN
WIND...60MPH
 
$$

JN

373 
WWUS55 KPSR 130540
SVSPSR

Severe Weather Statement
National Weather Service Phoenix AZ
1040 PM MST SAT AUG 12 2017

AZC013-130549-
/O.EXP.KPSR.SV.W.0056.000000T0000Z-170813T0545Z/
Maricopa AZ-
1040 PM MST SAT AUG 12 2017

...THE SEVERE THUNDERSTORM WARNING FOR MARICOPA COUNTY WILL EXPIRE AT
1045 PM MST...
                
The storm which prompted the warning has weakened below severe
limits, and no longer poses an immediate threat to life or property.
Therefore the warning will be allowed to expire.  However heavy rain 
is still possible with this thunderstorm. A Flash Flood Warning is 
in effect for areas that were included in this expiring Severe 
Thunderstorm Warning.

LAT...LON 3333 11240 3356 11267 3373 11242 3342 11210
TIME...MOT...LOC 0539Z 226DEG 12KT 3358 11227 

$$

JN

Area Forecast Discussion
National Weather Service Phoenix AZ
925 PM MST Sat Aug 12 2017

.UPDATE...Updated aviation discussion...

.SYNOPSIS...
Sufficient moisture remains in place this weekend supporting a few
showers and thunderstorms across central and eastern Arizona. On
Monday, a drying trend will end storm chances across the lower
elevations with only limited chances remaining across the higher
terrain. After Tuesday and through the end of the week, mostly clear
skies and dry conditions will prevail with near normal temperatures.

&&

.DISCUSSION...
A subtle midlevel shortwave embedded in westerly flow likely aided
by gravity wave action from overnight Mexican convection had
enhanced deep layer moisture convergence leading to scattered
showers across central Arizona earlier this morning. 12Z KPSR
sounding sampled a robust moisture intrusion through the H7-H5 layer
tapping a portion of the available 1500 J/kg MUCape. This shortwave
has dampened and moved east while more defined anti-cyclonic flow
and warming aloft attempts to advect east from western Arizona.
Despite this temporary unfavorable synoptic setup, substantial
moisture in a sfc-H7 layer still lingers through central and eastern
Arizona this afternoon.

More organized deep convection through much of central Arizona will
be difficult to come by later this afternoon and evening with
activity more focused through northern and far southeast Arizona.
The main exception will be terrain driven showers where the
environment has been more well mixed and upslope thermal
circulations are capable of briefly breaking inhibition aloft. Then
overnight, with moisture floating about the H7 layer and potential
gravity waves, a similar setup to this morning may exist where a
slug of 12 g/kg H7 moisture is saturated in the form of accas
showers. Several NAM based members depict this scenario though
certainly its not a foregone conclusion, and conceptually would
think any activity Sunday morning would be even more isolated and
weaker than this morning.

Through the day Sunday, deeper and stronger westerly flow will
impinge on the CWA with more intrusive drying eating away at the
current moisture profiles. The most notable drying will start above
the H7 level, but work to the sfc and erode boundary layer moisture
profiles through southeast California and western Arizona. The
biggest forecast challenge is determining the magnitude and quality
of moisture remaining over central Arizona during peak heating and
ahead of this deeper dry airmass. Both the GFS and NAM BUFR
soundings suggest 11-13 g/kg of moisture holding in the sfc-750mb
layer tomorrow afternoon, however the amount of drying (or lack
thereof) at the top of the boundary layer along with the influence
of any early day cloud cover could limit (or enhance) late afternoon
and evening convective potential. At this time, the preponderance of
high resolution ensemble members show only minimal activity Sunday,
though will need to closely monitor this time frame for not only
thunderstorms but outflow winds as well.

Starting Monday, the overall synoptic pattern through the western
Conus will resemble a mid/late September flow pattern more than
August with a progressive, deep negative height anomaly moving into
the intermountain West. By the afternoon, strong westerly flow
should have completely scoured away quality moisture with PWATs
falling below an inch at Phoenix and remarkably below 1/3 inch over
southeast California. Chopped away POPs Monday feeling convection
will be concentrated over the Rim and White while the deep westerly
flow steers any cells away from the forecast area.

Tuesday through Friday look be exceptionally dry for August with
surface dewpoints falling into the 40s and PWATS in a 0.25-0.75 inch
range. Even though we dry out, temperatures will be hindered by
unusually low heights and thicknesses aloft. In fact, H5 heights
only in a 584-588dm range will be common much of the week (typical
for late September, not mid August). Thus, high temperatures near
seasonal normals (or even a few degrees below) seem very likely with
overnight lows locally dipping to a few degrees below normal due to
the drier airmass and efficient nocturnal cooling. Some moisture may
start to seep back into southern Arizona as early as Friday, but
more likely next Saturday as the flow begins to shift more out of
the south to southeast.

&&

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

Outflows from thunderstorms that have developed over the higher
terrain to the north are now moving into the greater Phoenix area at
the present time. Gusty northerly winds in the 15-25 mph range can
be expected over the next couple of hours before becoming easterly
at/just after midnight. Thunderstorms developing over the west
valley at this time could also affect the terminals between now and
midnight, thus will be including VCTS in the terminals during this
period as well. Lesser chances for SHRA/TS after midnight as well,
but confidence is still too low at this point to include anything
more than VCSH at this time. Sct-Bkn mid/high cloud decks likely to
persist into Sunday morning before some clearing in the afternoon.
At this point, shower/TS chances look to be substantially less for
Sunday afternoon/evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No
Little aviation concerns over the next 24 hours as winds remain
southerly at KBLH and from the southeast at KIPL. Showers and storms
should stay well to the east of the terminals.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Tuesday through Saturday:
Unusually dry air will settle over the districts during this time
frame with almost no chance of showers or thunderstorms through the
week. Unlike most mid-monsoon breaks, temperatures will stay near
the seasonal average. With the introduction of drier air, minimum
afternoon humidity levels will fall back to a 10-20% range though
overnight recovery will remain fair to good. Upslope afternoon wind
gusts will be stronger than typical monsoon season levels Tuesday
and Wednesday with the passage of a early fall-like weather
disturbance through northern Arizona.

&&

.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...MO/Kuhlman
AVIATION...Percha
FIRE WEATHER...MO

Special Weather Statement
National Weather Service Phoenix AZ
750 PM MST SAT AUG 12 2017

AZZ538-539-559-130345-
Sonoran Desert Natl Monument AZ-Tonopah Desert AZ-Gila Bend AZ-
750 PM MST SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA COUNTY UNTIL 845 PM
MST...

At 749 PM MST, Doppler radar was tracking a strong thunderstorm near
Gila Bend Auxiliary Field, or 7 miles southeast of Gila Bend, moving
north at 5 mph.

Winds in excess of 40 mph, moderate to heavy rainfall and patchy
blowing dust will be possible with this storm.

Locations impacted include...
Gila Bend, Bosque, Sonoran National Monument, Big Horn, portions of
State Route 85 and Interstate 8 at and east of Gila Bend.

LAT...LON 3271 11239 3283 11273 3307 11270 3294 11227
TIME...MOT...LOC 0249Z 199DEG 6KT 3286 11262

JN

Special Weather Statement
National Weather Service Phoenix AZ
856 PM MST SAT AUG 12 2017

AZZ541-545-130500-
New River Mesa AZ-Cave Creek/New River AZ-
856 PM MST SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA COUNTY UNTIL 1000 PM
MST...

At 856 PM MST, Doppler radar was tracking an area of strong
thunderstorms over New River, moving northeast at 10 mph.

Winds in excess of 40 mph and moderate to heavy rainfall will be
possible with this storm.

Locations impacted include...
New River, Cave Creek, Seven Springs and Anthem.

LAT...LON 3402 11189 3392 11183 3383 11219 3393 11224
      3395 11224 3397 11219 3401 11218 3402 11216
      3404 11216 3405 11213
TIME...MOT...LOC 0356Z 244DEG 10KT 3395 11216

JN

Special Weather Statement
National Weather Service Phoenix AZ
910 PM MST SAT AUG 12 2017

AZZ537-538-540>542-544-130515-
Buckeye/Avondale AZ-Cave Creek/New River AZ-Tonopah Desert AZ-
Northwest Valley AZ-Deer Valley AZ-North Phoenix/Glendale AZ-
910 PM MST SAT AUG 12 2017

...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA COUNTY UNTIL 1015 PM
MST...

At 909 PM MST, Doppler radar was tracking an area of strong
thunderstorm over Sun City down through Buckeye. These storms
were nearly stationary.

Wind gusts of 50 to 55 mph and moderate to heavy rain will be
possible with these storms.

Locations impacted include...
Glendale, Peoria, Surprise, Avondale, Goodyear, Buckeye, El Mirage,
Youngtown, Sun City West, Waddell, Sun City, Litchfield Park, White
Tank Mountain Park, North Mountain Park, Liberty, Downtown Peoria,
Surprise Stadium, Arrowhead Mall and Downtown Glendale.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

&&

LAT...LON 3333 11259 3353 11281 3384 11231 3361 11200
TIME...MOT...LOC 0409Z 226DEG 2KT 3363 11227

JN