Severe Thunderstorm Warning 254, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
245 PM MST Thu Oct 6 2022

.SYNOPSIS...
Periodic thunderstorm chances will continue through early next week
as a low pressure system stalls along the Arizona-Mexico border.
While rainfall chances and coverage may vary more significantly on a
daily basis, gusty thunderstorm outflow winds will be far more
common. Otherwise, temperatures will remain within a few degrees
of normal through next week.

&&

.DISCUSSION...
Latest streamline analysis indicates the center of the mid-
tropospheric closed low has retrograded to a position near Puerto
Penasco. Numerous smaller vortices are evident in water vapor
imagery embedded within the larger cyclonic circulation and this
is producing areas of enhanced ascent across the region. Highest
PWATs across the Desert Southwest only top out at 1.2-1.4 inches.
However, SPC mesoanalysis indicates a pocket of very cold air
aloft north of Yuma, yielding steep mid-level lapse rates and
uninhibited values of MLCAPE approaching 2000-3000 J/kg.
Consequently, convection has initiated rapidly this afternoon and
some of the storms have been quite strong with MRMS MESH
indicating 1+ inch hail. Conditions also remain favorable for
strong/severe winds, given the 50+ percent probabilities of 35 mph
winds per the latest HREF, particularly along a line extending
from Pima County westward to El Centro.

Forecast is largely weighted to the time-lagged HRRR, which has
performed well recently, not surprising given the synoptic
component to the forcing. This points to two main areas of concern
the rest of today, where activity is already ongoing across
southwestern Arizona/southeastern California and from Phoenix
north and eastward. This potential is reflected in the NBM PoPs,
which have jumped markedly to around 30 percent near Yuma. Across
south-central Arizona, storms are generally not expected to be as
organized or intense as those across southwestern Arizona.
Nevertheless, there is a discernible signal for an outflow
boundary capable of initiating additional cells and producing
strong winds and blowing dust. PWATs remain well above average and
some persistent cells will also be capable of producing localized
flash flooding. Unlike Wednesday night, there is higher
uncertainty that activity will fizzle out later this evening.

&&

.PREVIOUS DISCUSSION...
Subtle details will be just about the only thing differentiating
the regional pattern Friday through Sunday with pronounced deep
easterly flow situated in the northern half of the aforementioned
circulation. Total moisture may increase somewhat the next couple
days, but doesn't look to exceed 7-8 g/kg though should become
better mixed through the boundary layer. However concurrently,
mid-level lapse rates appear to deteriorate as the cold core
weakens and the system begins filling yielding progressively lower
instability values. Nevertheless, the presence of well organized
vorticity lobes should enhance lift during peak heating within
focused areas. While details become more uncertain further into
the future, there has been recurring evidence one such regions of
stronger vorticity advection will surge into SE AZ Friday forcing
storm formation around the Tucson area. As has been the case
recently, strong outflow winds and blowing dust would be the most
prevalent outcome (and this would especially be the case along the
I-10 corridor). Should vorticity be mistimed or aligned too far
south, another opportunity may present itself Saturday with
similar wind and dust impact potential.

As the cutoff low eventually opens and becomes sheared downstream
next week, convective potential should gradually wane across the
region though automated NBM output is slower to relinquish POPs
given the range of ensemble solutions. Regardless, there is growing
evidence that lapse rates will suffer further while boundary layer
mixing ratios erode closer to 6 g/kg and total column PWAT fall into
a 0.75-1.00 inch range. If this becomes the case, it will take an
even stronger shortwave and better dynamics to realize rainfall
chances the remainder of the week.

&&

.AVIATION...Updated 1720Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

IMPACTS TO METRO TERMINALS:
 1) 10-20% chance of showers/storms between 22Z and 4Z this
    evening.
 2) ~30% risk of outflow wind gusts exceeding 30KT between
    22Z and 4Z this evening.

Easterly winds should continue for much of the afternoon, with
only about a 20% chance PHX has a short time of westerlies after
20Z. From around 22Z to 4Z, hi-res models indicate that some
storms will try to develop around the area. Main threat would be
gusty winds 30-40KT in the strongest activity. This will be on an
isolated, hit-or-miss basis and not all terminals will see storms.
Higher chance of brief gusty winds than an actual storm overhead.
Later tonight, light easterly flow resumes and continues into much
of tomorrow. Another chance of storms / outflow winds appears to
be with us at the tail-end of the TAF package, so look out for
further tweaks on that time period as we get a little closer. CIGs
should remain aoa 10KFT, perhaps only slightly below that if a
storm is overhead.

Southeast California/Southwest Arizona including KIPL and KBLH:
IPL: Expect quiet conditions with ESE winds through late
afternoon. Storms are expected E/NE of the terminal by around 0Z.
These may push outflow winds of 30+KT into the area around 1Z or
so, with around a 40% risk of these wind gusts occurring at the
terminal. Blowing dust would accompany this. Quieter conditions
return overnight.

BLH: Iso storms will likely be E/SE of the terminal later today,
with around a 20% risk of outflow winds exceeding 30KT. This is
currently not explicit in the TAF due to low confidence per hi-res
model guidance. Otherwise, extended periods of light/variable
winds can be expected.

Cloud cover at both CA terminals will be aoa 10KFT throughout,
except near any storm.

&&

.FIRE WEATHER...
Unsettled conditions will continue for most districts through at
least the beginning of next week with occasional shower and
thunderstorm chances. Coverage of wetting rains may be somewhat
limited as compared to expanse of strong, gusty outflow winds. In
general, storms chances in eastern districts will be greater and
more prolonged than western districts. Temperatures will not stray
terribly far from the seasonal normal through next week. Relatively
humid conditions will continue with afternoon minimum humidity levels
mostly in a 25-50% range following good to excellent overnight
recovery of 50-90%. Aside from thunderstorm outflow, winds will
favor an easterly direction more often than the typical afternoon
upslope westerly.

&&

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

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...18
AVIATION...Heil
FIRE WEATHER...18

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Special Weather Statement
National Weather Service Phoenix AZ
423 PM MST Thu Oct 6 2022

AZZ541-542-544-546>549-551-553-555-070000-
Fountain Hills/East Mesa AZ-Scottsdale/Paradise Valley AZ-
Cave Creek/New River AZ-Northwest Pinal County AZ-
Southeast Valley/Queen Creek AZ-East Valley AZ-
Apache Junction/Gold Canyon AZ-Deer Valley AZ-
Rio Verde/Salt River AZ-North Phoenix/Glendale AZ-
423 PM MST Thu Oct 6 2022

...Strong thunderstorms will impact portions of Maricopa and Pinal
Counties through 500 PM MST...

At 423 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from Fountain Hills to near Usery Mountain Park to
near Queen Creek. These storms were nearly stationary.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Phoenix, Mesa, Chandler, Scottsdale, Gilbert, Tempe, Apache Junction,
Fountain Hills, Paradise Valley, Gold Canyon, East Mesa, Queen Creek,
Tempe Marketplace, Granite Reef Dam, Falcon Field Airport, Salt River
Indian Community, Usery Mountain Park, San Tan Village Mall, San Tan
Valley and Seville.

This includes the following highways...
AZ Route 51 near mile marker 13.
US Highway 60 between mile markers 175 and 205.
AZ Route 87 between mile markers 162 and 196.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3363 11201 3325 11187 3307 11161 3325 11139
      3356 11155 3376 11179
TIME...MOT...LOC 2323Z 024DEG 4KT 3360 11177 3344 11162 3326 11156

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

SDB

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
437 PM MST THU OCT 6 2022

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

0410 PM     DUST STORM       1 WSW IMPERIAL          32.83N 115.58W
10/06/2022                   IMPERIAL           CA   ASOS

            ASOS STATION KIPL IMPERIAL. LESS THAN 1/4
            MILE VISIBILITY IN BLOWING DUST.

&&

SB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
438 PM MST THU OCT 6 2022

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

0421 PM     NON-TSTM WND GST 2 NNE SEELEY            32.82N 115.67W
10/06/2022  M54 MPH          IMPERIAL           CA   AWOS

            AWOS STATION KNJK EL CENTRO NAF.

&&

SB