Special Weather Statement, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
210 PM MST TUE AUG 2 2016

.SYNOPSIS...
An excessively humid airmass will continue to cover the region the
next couple days, with the best chance of showers and thunderstorms
over Arizona. While some areas may not see rain, locally heavy
rainfall is possible in some locations. A drier and more stable
airmass will begin to spread into the area during the end of the
week, pushing thunderstorm activity into eastern Arizona. An even
drier and warmer airmass will then cover the region over the weekend
and into early next week with very limited thunderstorm activity.

&&

.DISCUSSION...
An unusually moist airmass continues to blanket virtually all of
southern and central Arizona this morning with 12Z KPSR and KTWC
soundings sampling near sfc mixing ratios at least 15 g/kg and mean
sfc-H7 mean mixing ratios at least 13 g/kg. Throughout the total
atmospheric column, PWATs measured at 2.0 inches are easily a record
for the date, and some of the highest historical values ever
recorded at these stations. Sounding data showed nearly moist
adiabatic lapse rates; and given the moist environmental profiles,
its not surprising that scattered showers/storms continued to
percolate throughout the region even during non-traditional times.

Meanwhile, a weak H7-H5 vorticty center earlier over Pima County
was becoming more diffuse and possibly lifting into the White
Mountains. At the same time, a more well defined inverted trough
over the northern Gulf of California leading to general difluence
aloft amid extremely weak tropospheric wind profiles. Moderate CAPE
in the 0-3km layer was still observed in objective analysis with
excessive moisture profiles below the freezing level yielding
efficient rain producers. Thus while cloud cover has largely limited
growing instability over parts of central Arizona, inhibition was
minor to begin with and areas to the west of the thickest cloud
coverage (i.e. a line roughly from Gila Bend-Buckeye-Wickenburg)
would conceptually stand the most likely chance to experience rapid
convective growth this afternoon with locally heavy rainfall.

Much like early this morning, convective activity may continue to
pulse through the overnight hours into Wednesday as any small
perturbation or weak boundary would easily be capable of releasing
modest instability. Overall coverage tonight should generally wane
with little large scale forcing mechanisms, but confidence in any
given model output is quite low. HRRR had earlier depicted the most
reasonable outcomes, though recent iterations have a surprisingly
lack of convection given the current observational trends. High
resolution NMM cores seem to be overly aggressive with convection,
and possibly the 00Z NSSL ARW core shows slightly better realism.

Overall, a blend of SREF and high resolution ensemble output was
utilized to depict rainfall chances through Wednesday afternoon with
most guidance packages suggesting convective activity less robust
over lower elevations. However, given the very high moisture content
currently over the forecast area, there is serious reservation on
how rapidly this could be scoured out. Numerical guidance seems to
identify this fact while raw model output is more pessimistic about
organized activity. Have blended these guidance packages to achieve
a moderately confident forecast which doesn't completely discount
storm chances through Thursday.

Friday through Tuesday: A warmer and drier airmass will continue to
spread across the forecast area as deeper westerly flow envelops the
SW Conus. Afternoon temperatures at lower elevations will gradually
warm into 108 to 110 degree range, though some uncertainty exists
given how rapidly low level moisture advects eastward. Only a slight
chance of afternoon and evening showers and thunderstorms are
forecast over the mountains of southern Gila County zone 24 near the
higher elevations of the White Mountains.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:
Abundant monsoon moisture will keep showers and isolated
thunderstorms near Phoenix terminals through the period, with the
highest coverage in the western valley, especially over the White
Tank mountains. This moist atmosphere will also aid in keeping
clouds aoa 8kft in place. In addition, this abundant cloud cover
will allow easterly winds to take dominance through the entire
period, with a more southerly component between 21Z and 02Z.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will remain primarily out of the south-southwest at both TAF
sites with ceilings aoa 10kft. With a very moist atmosphere in place
showers and thunderstorms, especially over the KBLH airport, cannot
be ruled out this afternoon into tomorrow morning.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday...
A drying trend will commence with minimum humidities on Friday
around 10 to 20 percent, slowing dropping into the 8 to 15 percent
range by Tuesday. Light winds and a very moist environment in place
prior to this period will really aid in keeping the fire threat low
Friday through Tuesday.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not likely.

&&

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

&&

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DISCUSSION...MO/Vasquez
AVIATION...Hernandez
FIRE WEATHER...Hernandez

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
458 PM MST TUE AUG 2 2016

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

0446 PM     HEAVY RAIN       5 S NEW RIVER           33.85N 112.14W
08/02/2016  M1.00 INCH       MARICOPA           AZ   TRAINED SPOTTER

            . THE DURATION OF THE HEAVY RAIN EVENT WAS 1
            HOUR.

&&

NWS PHOENIX AZ
IRIS SYSTEM

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PHOENIX AZ
458 PM MST TUE AUG 2 2016

AZZ023-030045-
GREATER PHOENIX AREA AZ-
458 PM MST TUE AUG 2 2016

...SIGNIFICANT WEATHER ADVISORY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A

SIGNIFICANT WEATHER ADVISORY FOR...
  MARICOPA COUNTY

UNTIL 545 PM MST

AT 458 PM MST...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM OVER
GLENDALE. THIS STORM WAS NEARLY STATIONARY.

WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...
PHOENIX...GLENDALE...TEMPE...AVONDALE...GOODYEAR...EL MIRAGE...
PARADISE VALLEY...TOLLESON...YOUNGTOWN...CASHION...SUN CITY...
LAVEEN...LITCHFIELD PARK...DOWNTOWN GLENDALE...SKY HARBOR AIRPORT...
GLENDALE SPORTS COMPLEX...DOWNTOWN PHOENIX...SOUTH PHOENIX...
CAMELBACK RANCH AND METRO CENTER.

LAT...LON 3338 11195 3339 11239 3363 11232 3361 11200
TIME...MOT...LOC 2358Z 188DEG 0KT 3351 11219

SAWTELLE