Flash Flood Warning 42, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
455 AM MST Wed Sep 13 2023

.UPDATE...Updated 12z Aviation Discussion...

&&

.SYNOPSIS...
Thunderstorm chances will exist through today before drier
conditions settle in going forward into tomorrow. Thunderstorm
chances will remain focused across parts of central and eastern
Arizona today with some thunderstorms potentially becoming strong
to severe. Chances for rain drop to near zero for the end of the
week with temperature gradually trending upward through the
weekend.

&&

.DISCUSSION...
It was a very active evening across the Valley Tuesday as strong to
severe thunderstorms developed and produced damaging winds and small
hail. There were many reports of damage with thousands of people
losing power from the storms. There were no major reports of flash
flooding with these thunderstorms with amounts across the metro area
generally up to 0.25-0.50". However, the heaviest totals occurred
across the northern foothills where amounts as high as 1.50-2.50"
were observed. At Sky Harbor, 0.02" of rain were recorded which now
brings the monsoon season total up to 0.15".

Early morning radar shows quieter conditions now prevailing across
the Phoenix area with thunderstorm activity now to the east over the
higher terrain areas. Objective analysis shows EBWD values to around
40 kts, which has allowed for some organized thunderstorms with a
few strong to severe thunderstorms occurring earlier this morning.
Meanwhile out to the west of the Phoenix area, IR imagery show
mostly clear conditions in place where drier, subsident air has
prevailed. RAP analysis this morning shows PWAT values less than an
inch across southeast California while the greatest values reside
across south-central Arizona where values are around 1.60", which is
above the 90th climatological percentile. This anomalous moisture
has allowed for thunderstorms to be heavy rainfall producers, but
quicker storm motion has precluded any greater widespread flooding
threat. However, areas that have seen thunderstorms train over the
same areas have experienced very heavy rainfall amounts and thus
have led to flash flooding concerns.

As we head through the rest of the morning, ongoing showers and
thunderstorms are expected to mostly dissipate before additional
activity is possible by this afternoon. The latest HREF paintball
plots show good agreement in additional thunderstorm activity across
parts of south-central Arizona heading into this afternoon, but the
bulk of this is expected to mostly be focused further east across
areas such as the southern Gila County high terrain and into
southeast Arizona. Forecast soundings indicate a favorable
thermodynamic environment for this afternoon with HREF MUCAPE values
around 1,000 J/kg along with minimal inhibition and steeper lapse
rates. Combined with forcing associated with a weak shortwave will
promote thunderstorm development, some of which may become strong to
severe. SPC has highlighted parts of central and eastern Arizona in
a Marginal Risk of severe weather today with the primary threats
being damaging winds and isolated severe hail.

By early Thursday, a drier airmass will begin to take hold with
ensemble guidance showing PWATs falling below an inch. This will
act to eliminate rain chances through the rest of the week with
NBM PoPs near zero. Ensemble guidance show good agreement in
ridging building into the western CONUS for the end of the week
with 500 mb heights across the forecast areas climbing upwards of
588-590 dm. This will lead to temperatures gradually rising near
to slightly above seasonal normals heading into this weekend.

&&

.AVIATION...Updated at 0540Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Most of the TSRA activity has now moved eastward, with mainly
quiet conditions prevailing currently. Winds will generally
prevail from the E to ENE through the morning hours with speeds
aob 10 kts. The forecast for this afternoon becomes more uncertain
as there is the potential for widely scattered thunderstorm
activity to develop mainly south and east of the terminals.
Confidence is low for any TSRA to directly affect the terminals,
especially for KPHX and KIWA. Therefore, only VCSH have been
mentioned in the TAFs at this time. Winds are likely to switch out
of a westerly component this afternoon before switching back out
of the east by this evening with speeds generally aob 10 kts
although if thunderstorms do develop close enough, gusty, erratic
outflow winds will be more likely with around a 30% chance of
gusts over 30 kts. Mainly SCT to occasionally BKN mid-level clouds
will prevail through this afternoon before clearing skies this
evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are expected through the forecast
period. Winds will favor a westerly component at KIPL and a south
to southwest component at KBLH with speeds generally aob 10 kts.
Clear skies expected through the period.

&&

.FIRE WEATHER...
Showers and thunderstorms will be possible across parts of south-
central Arizona today with the greatest chances remaining across
the southern Gila County high terrain. Gusty erratic winds along
locally heavy rainfall may accompany any stronger thunderstorms
that develop. Drier conditions begin to settle in heading into
Thursday, reducing rain chances to near zero through the remainder
of the week. Min RHs will drop over the next several days with
values around 15-25% by the end of the week. Outside of any
thunderstorms, winds will generally favor diurnal tendencies.

&&

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

DISCUSSION...Smith
AVIATION...Lojero
FIRE WEATHER...Smith

Special Weather Statement
National Weather Service Phoenix AZ
523 AM MST Wed Sep 13 2023

AZZ546>549-551-555>558-131300-
Fountain Hills/East Mesa AZ-Scottsdale/Paradise Valley AZ-
Mazatzal Mountains AZ-Tonto Basin AZ-East Valley AZ-
Southeast Valley/Queen Creek AZ-Apache Junction/Gold Canyon AZ-
Rio Verde/Salt River AZ-Pinal/Superstition Mountains AZ-
523 AM MST Wed Sep 13 2023

...A strong thunderstorm will impact portions of Gila, Maricopa and
Pinal Counties through 600 AM MST...

At 521 AM MST, Doppler radar was tracking a couple of clusters of
strong thunderstorms between Apache Junction and Tortilla Flat,
moving northeast at 30 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Mesa, Apache Junction, East Mesa, Granite Reef Dam, Gold Camp, Falcon
Field Airport, Lost Dutchman State Park, Goldfield, Usery Mountain
Park, Saguaro Lake, Canyon Lake, Superstition Mountains, Goldfield
Ranch, Four Peaks, Kings Ranch, Apache Lake, Salt River Tubing
Recreation Area, and Tortilla Flat.

This includes the following highways...
US Highway 60 between mile markers 189 and 202.
AZ Route 87 between mile markers 184 and 204.
AZ Route 202 between mile markers 20 and 34.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3378 11130 3348 11113 3330 11162 3354 11179
TIME...MOT...LOC 1221Z 246DEG 26KT 3349 11155

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

GL

Preliminary Local Storm Report
National Weather Service Phoenix AZ
554 AM MST Wed Sep 13 2023

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

0900 PM     Tstm Wnd Dmg     4 NW East Mesa          33.46N 111.73W
09/12/2023                   Maricopa           AZ   Broadcast Media

            Multiple small aircraft damaged, with some
            even completely flipped over. There was also
            significant roof damage to the hangar.

&&

GL

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