Severe Thunderstorm Warning 244, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
1025 AM MST Thu Oct 6 2022

.UPDATE...18Z Aviation Discussion (Below)...

&&

.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. Temperatures near to slightly above average will cool
modestly over the weekend.

&&

.DISCUSSION...
As the Conus pattern enters a blocking regime, a broad cyclonic
circulation with numerous embedded vorticity lobes was clearly
evident on early morning WV imagery spinning over the Southwest.
This weak negative height anomaly will attempt to consolidate along
the international border through the weekend while comprising the
southern portion of a high amplitude Rex block. However, individual
PV centers will continue to rotate about the larger circulation with
arms of vorticity extending outward and providing periodic forced
ascent across the region. Models remain in excellent agreement
showing this stalled conglomeration of smaller circulation centers
wobbling just south of the forecast area, and only being absorbed in
downstream subtropical flow next week resulting in a prolonged
period of seasonally unusual unsettled weather.

One such better defined PV center was diving south along the
Colorado River forcing downstream ascent over south-central AZ with
favorable jet dynamics releasing elevated MUCape (~1000 J/kg) behind
an outflow boundary in an environment of steep midlevel lapse rates.
This cluster of showers/storms should follow the leading edge of
vorticity advection aimed towards higher instability air in northern
Mexico through the morning hours. With this vorticity center
pivoting south into NW Sonora, objective analysis suggests drier
air being pulled south as well. However, a plume of better 10-12
g/kg mixing ratios and weakly capped MLCape (1000-1500 J/kg) should
still reside in far SW AZ/SE CA, and be one focus area for isolated
deep convection. Modest upper level energy and DCape values near
1500 J/kg will support the potential for a strong to severe wind
gust with any isolated storm.

Elsewhere, another PV center should rotate from SE AZ into western
NM and act as a secondary synoptic focusing mechanism for showers
and storms. HREF membership clusters most activity around the White
Mountains though in an area of much lower moisture content and
instability. It appears probable that a few storms will drift into
Gila County though becomes more uncertain if coverage and intensity
can be maintained. Much of the CWA may actually fall between these
two features and into a somewhat less favorable ascent structure,
albeit still with little inhibition and steep lapse rates.
Nevertheless, gusty outflow winds from distant storms seem more
likely though HREF probabilities are quite tempered in the latest
iteration.

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 afomentioned 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, midlevel 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...18
AVIATION...Heil
FIRE WEATHER...18

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Special Weather Statement
National Weather Service Phoenix AZ
1219 PM MST Thu Oct 6 2022

AZZ535-062000-
Southeast Yuma County AZ-
1219 PM MST Thu Oct 6 2022

...A strong thunderstorm will impact portions of south central Yuma
County through 100 PM MST...

At 1218 PM MST, Doppler radar was tracking a strong thunderstorm 19
miles south of Wellton, or 25 miles southeast of Fortuna Foothills,
moving west at 15 mph.

HAZARD...Wind gusts up to 50 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.

This storm will remain over mainly rural areas of south central Yuma
County.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3221 11389 3235 11435 3238 11437 3250 11431
      3242 11390 3220 11383
TIME...MOT...LOC 1918Z 101DEG 13KT 3240 11411

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

Heil

Special Weather Statement
National Weather Service Phoenix AZ
1247 PM MST Thu Oct 6 2022

AZZ531-532-536-062030-
Gila River Valley AZ-Kofa AZ-Yuma AZ-
1247 PM MST Thu Oct 6 2022

...A strong thunderstorm will impact portions of southwestern La Paz
and central Yuma Counties through 130 PM MST...

At 1247 PM MST, Doppler radar was tracking a strong thunderstorm 16
miles southeast of Yuma Proving Ground, or 16 miles east of Martinez
Lake, moving west at 10 mph.

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.

This storm will remain over mainly rural areas of southwestern La Paz
and central Yuma Counties.

This includes AZ Route 95 between mile markers 49 and 59.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3303 11407 3284 11405 3281 11434 3303 11437
TIME...MOT...LOC 1947Z 088DEG 10KT 3293 11419

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

Heil