Severe Thunderstorm Warning 66, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
316 PM MST Thu Aug 11 2022

.SYNOPSIS...
A 15 percent chance of widely isolated to scattered mostly
distant and high terrain storms continues this afternoon in
Phoenix, with better 30 to 50 percent chances across the high
terrain areas. Storm chances then gradually increase this evening
through tomorrow and the weekend with locally heavy rainfall,
localized flash flooding, gusty winds and patchy blowing dust
possible. Near to slightly below normal highs will fall further
below normal over the weekend and through early next. Storm
chances for next week remain moderate.

&&

.DISCUSSION...
The midlevel anticyclone remains favorably located near the S-Cent
Rockies with moist SE-E undercutting flow through the mid-upper
levels aloft. WV imagery reveals a very moist airmass across the
region with upstream E wave disturbance(S) advancing W through NM.
Early afternoon radar revealed convection sparking E-NE of Phoenix, N
and SE AZ. Afternoon ACARS soundings showed an anomalously moist
airmass with PW maintaining near 1.7->1.9" along with a near moist
adiabatic, slightly worked-over and conditionally unstable
profile. Mesoscale analysis indicated PW of 1.5->2" and mean W of
12->14 g/kg across the region. MU and SB CAPE readings were to
~1.3K->1.5K j/kg around Phoenix and >2-2.5k j/kg across the W
deserts.

Under mostly clear skies, morning heating across Phoenix and the
lower deserts has been stronger today than recent mornings. Models
also indicate temporary subsidence around Phoenix and the lower
deserts this afternoon. A 15 percent chance of widely isolated to
scattered mostly distant and high terrain storms continues this
afternoon in Phoenix, with better 30 to 50 percent chances across
the high terrain areas. Recent HRRR runs have latched onto a late
afternoon E outflow pushing into the Phoenix Metro with the
potential for locally gusty winds. This is in good agreement with
current radar trends.

Storm chances then gradually increase this evening through tomorrow
and the weekend with locally heavy rainfall, localized flash
flooding, gusty winds and patchy blowing dust possible. The WPC day
2 ERO for tomorrow/Fri also features a large "Slight Risk" area
of excessive rain fall for most of AZ. This is associated with the
next E wave out of NM.

HREF and members are fairly bullish on pronounced convection with
locally heavy rainfall developing tomorrow/Fri afternoon across S
Gila Cty and near/E of Globe and burn scar areas (and the
Mogollon Rim and SE AZ) before descending into the lower deserts
and parts of the Phoenix Metro during the evening hours. HREF wind
speeds for Fri evening feature a pair of fairly robust converging
outflows, one from the NE and the other from the SSE. The
resulting low level convergence through Pinal and Maricopa Cty,
coupled with the UL disturbance, would support pronounced
storms/convection for the Phoenix Metro and lower deserts
spreading west of Phoenix, including into parts of W-SW AZ and SE
CA, well into the night. The preferred WPC storm total QPF for
Phoenix on Fri is ~0.10-0.15" and ~0.3-0.5" for both the E AZ high
elevations and parts of the western deserts. The HREF shows a
50-70% chance for 3-hr QPF >1.0" for the E AZ high terrain for
Fri evening and a corresponding 10-30% chance for Phoenix and the
lower deserts. This represents a good signal for locally heavy
rainfall and additional localized flash flooding in the high
country and the lower deserts.

For the weekend, ensembles are latching onto a slightly larger E
wave on Sat evening and Sun moving from NM to AZ in general. The
preferred NBM and WPC solutions feature an increase in POPs while
maintaining healthy storm total QPF for Sat evening and Sun
morning comparable to the aforementioned Fri evening/Sat morning
storm total QPF.

At some point early next week, the pattern will begin to shift
with the sub-tropical high to our northeast weakening, while a
weak trough possibly sets up off the southern California coast.
This scenario may not bring much of a change to our area with
models continuing to show adequate moisture levels for storms, but
overall forecast confidence is low due to the change in the upper
level pattern and some model differences. Temperatures are
expected to cool off slightly at some point over the weekend into
early next week with forecast highs closer to 100 degrees due to
anticipated more active monsoon conditions.

&&

.AVIATION...Updated 1740Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light winds will completely veer to the west by early this
afternoon. Another day of storms across northern and southeastern
Arizona will likely cause outflow boundaries to make a run for the
area. Currently, there appears to be the potential for a weaker
NNE outflow first, sometime in the mid to late afternoon.
Confidence is lower on this outflow, so have excluded in this TAF
package. If it were to come to fruition, KSDL and KDVT would have
the better chances. Models are starting to delay and weaken the
later outflow from the southeast. However, it still looks to be
the more dominant one and the one that would have the better
chances of popping up some isolated showers/convection over
terminals, so have kept mention of this outflow and associated
vicinity showers in this TAF package. There are also signs of some
nocturnal activity late tonight into early tomorrow morning, but
confidence of this happening is also too low to include in this
TAF package. Regardless, any shower/storm that develops will be
capable of producing gusty erratic winds, blowing dust, and
locally heavy rainfall. Wind speeds with activity this
afternoon/evening should generally stay below 35 mph, with a
10-30% chance of speeds exceeding that.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will generally favor the south-southeast. Chances for
showers and thunderstorms this afternoon and evening are around
20% or less at the terminals. However, any thunderstorm that
develops would be capable of gusty erratic winds, blowing dust,
and locally heavy rainfall. Skies will remain mostly cloudy
through the TAF period with ceilings mainly aoa 10 kft.

&&

.FIRE WEATHER...
Ample monsoonal moisture is expected to persist through at least
the first half of next week keeping the fire danger threat low.
This moist airmass will continue to yield elevated humidities
with afternoon minimum RH values mostly in a 30-35% range,
locally higher, and good overnight recovery. Chances for wetting
rains will continue for most areas almost daily. Winds for the
most part will remain light, with the exception of thunderstorm
outflows generating stronger gusts.

&&

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

DISCUSSION...Sawtelle/Kuhlman
AVIATION...Feldkircher
FIRE WEATHER...Kuhlman

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1234 PM MST THU AUG 11 2022

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

0616 PM     TSTM WND GST     5 S YUMA                32.63N 114.62W
08/10/2022  M68 MPH          YUMA               AZ   AWOS

            [DELAYED REPORT] AWOS STATION KNYL YUMA
            REPORTED A 68 MPH WIND GUST.

&&

BF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1238 PM MST THU AUG 11 2022

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

0552 PM     DUST STORM       5 WSW CITRUS PARK       33.51N 112.52W
08/10/2022                   MARICOPA           AZ   TRAINED SPOTTER

            [DELAYED REPORT] TRAINED SPOTTER REPORTED
            HALF MILE VISIBILITY IS BLOWING DUST.

&&

BF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1240 PM MST THU AUG 11 2022

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

0600 PM     HEAVY RAIN       1 SW TONOPAH            33.49N 112.94W
08/10/2022  E0.50 INCH       MARICOPA           AZ   TRAINED SPOTTER

            [DELAYED REPORT] TRAINED SPOTTER REPORTED
            HALF AN INCH OF RAINFALL IN 30 MINUTES AND
            MINOR FLOODING IN BACKYARD.

&&

BF