Severe Thunderstorm Warning 48, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
435 PM MST Wed Jul 24 2024

.Update...Updated 00Z Aviation

&&

.SYNOPSIS...
A strong ridge of high pressure over the region will continue to
result in above normal temperatures across south central Arizona
with excessive heat conditions continuing along and west of the
Lower Colorado River Valley. Moisture levels will improve today
and Thursday, resulting in more active thunderstorm activity
across south central and southeastern Arizona. Strong to severe
thunderstorms are expected this afternoon and evening, primarily
across south central Arizona with the primary threats being strong
winds, dense blowing dust, and locally heavy rainfall. Drier
conditions are expected to arrive late this week into this weekend
with slightly cooler temperatures anticipated.

&&

.DISCUSSION...
Afternoon objective analysis showed the subtropical ridge of high
pressure centered near southern Nevada and northwest Arizona,
promoting northeasterly flow aloft over south-central Arizona. Radar
earlier this morning was showing isolated elevated convection across
parts of Yuma and Imperial Counties, but has since dissipated with
new convection firing along terrain features such as the Kofas and
Chocolate Mountains. The latest ACARS sounding and the 12Z PHX
sounding showed an uptick in moisture into the region, particularly
in the 500-700 mb layer, compared to 24 hours ago with PWATs near
1.7". The higher moisture content and increase in instability across
central and southeastern Arizona will act to promote greater and
more robust coverage of thunderstorms this afternoon and evening.

The 12Z HREF depicts better instability for this afternoon and
evening as MUCAPE values climb upwards of 1000-1500 J/kg. Forecast
soundings also show inverted-V profiles and DCAPE values climbing
upwards of 1500-1800 J/kg, which will support thunderstorms capable
of producing strong to severe downbursts along with strong outflows
emanating from these thunderstorms. HREF paintball plots show
good confidence amongst its members in thunderstorms continuing to
initiate across the Mogollon Rim and across southeast Arizona
this afternoon. HREF member agreement decreases in regards to
thunderstorm activity as outflows descend into the lower deserts,
but there is still good indication of thunderstorm development
into parts of the south-central Arizona lower deserts heading into
this evening with forecast soundings showing little CIN. Outflows
emanating from the high terrain north and east of Phoenix and
outflows from southeast Arizona may collide over the lower deserts
this evening and further help to enhance thunderstorm coverage
across parts of south-central Arizona. Outflows collisions will
have the ability to lead to more widely scattered robust
convection across the lower deserts through the evening with up to
a 50-70% chance for winds to exceed 35 mph and up to a 10% chance
to exceed 58 mph. Given the favorable thermodynamics, potential
for strong outflows/outflow collisions, and favorable inverted-V
profiles, SPC has issued a Severe Thunderstorm Watch for Maricopa,
Pinal, and Gila Counties through 9 PM MST. Strong to severe wind
gusts will be the primary threat with thunderstorms, which could
lead to areas of dense blowing dust. Therefore, a Blowing Dust
Advisory is in effect for portions of northwest Pinal County and
the far southern/southeastern fringes of the metro. Additionally,
locally heavy rainfall with thunderstorms could lead to isolated
instances of flash flooding.

.PREVIOUS DISCUSSION...

By Thursday, the subtropical high will begin to sag southward and
end up centered over N AZ. As this occurs, mid-lvl hghts/thicknesses
will rise with 850 mb temps peaking around 30-31C across much of
the region. This will allow temperatures to climb a degree or two,
especially across the western deserts with highs peaking around
115- 117F. Coincidentally, major HeatRisk will increase in
coverage across southeast CA and southwest AZ. Meanwhile, highs
should again range from 109F-113F in the Phoenix Metro area. The
overall steering flow is not expected to change much on Thursday
with the mid-level flow still remaining out of the east to
northeast. Global models continue to indicate a strong vortmax
moving south and west along the eastern periphery of the high
Thursday afternoon and evening. Therefore we will likely see
another round of convection developing across the Rim Country and
White Mountains. There is uncertainty regarding storm coverage
across the lower deserts depending on what happens today and if
the atmosphere will be able to recover. However, all indications
from high-res guidance point to another active day. Latest NBM
PoPs range from 30-40% for the central deserts and up to 60% for
the higher terrain of eastern and southeastern AZ on Thursday
evening. The main risks will again be strong wind gusts and
blowing dust as outflow boundaries converge over southcentral AZ.

Ensemble guidance continues to be consistent in indicating an upper-
level trough progressing into the Great Basin Region beginning on
Friday. This will cause the subtropical ridge to become displaced
further southward towards the international border while also
weakening in the process. This pattern shift will result in drier
westerly flow to settle in, dropping moisture levels. As a result, a
decrease in monsoonal thunderstorm activity is likely, with activity
mostly confined to far eastern and southeast AZ for Saturday and
Sunday. Temperatures will also cool by a few degrees as hghts aloft
diminish overhead. Therefore, the excessive heat should come to an
end by Friday. Highs this weekend will actually be largely below
110F. By early next week, the ensembles indicate that the
subtropical ridge will quickly rebound and move back into the Four
Corners region. At the same time, there are still indications from
both the GFS and ECMWF deterministic model solutions of a potent
inverted trough moving into the region from Mexico. If this solution
comes to fruition, then we will see a better chance for widespread
thunderstorm activity across the southern half of AZ early next week.

&&

.AVIATION...Updated at 2335Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Hi-res data shows multiple outflow traversing the metro through
about 06Z tonight, first from the NE/E, then from the N/NW. Recent
guidance now shows a much weaker NE'rly outflow, but has increased
the strength the secondary boundary, which could potentially push
gusts upwards of 30-35 kts, primarily at KSDL and KDVT. There are
still hints of SE'rly outflow impacting some terminals early
tonight, mainly KIWA, but confidence regarding this feature is
much lower than in previous TAF forecasts. However, if this SE'rly
outflow becomes the dominant boundary, the potential for reduced
visibilities due to blowing dust increases. Regardless, winds
25-35 kts appear likely through early tonight, the main question
that remains is where these winds will originate from. Due to the
uncertainty of the forecast, amendments will likely be needed
throughout the next several hours. SHRA ans TSRA in the vicinity
and over terminals is also a possibility (30-40%), but will be
heavily dependent on the strength of potential outflows. If
convective activity does initiate over the metro, the best timing
to see storms looks to be between 03-07Z. SCT-BKN skies can be
expected through tonight, with the lowest bases around 10k ft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns are expected during the TAF period.
Outside of a switch to the S/SW this evening, potentially caused
by an outflow from a distant thunderstorm, winds at IPL should
follow typical diurnal trends. Winds may gust 20-25 kts at times
with the above mentioned feature, but speeds should quickly
diminish thereafter. At BLH, diurnal trends will prevail, but an
E'rly outflow cannot be completely ruled out tonight, but
confidence surrounding this is low at this time. FEW-SCT mid and
high level clouds will be present through much of the forecast
window.

&&

.FIRE WEATHER...
Scattered showers and thunderstorms are expected to develop this
afternoon and evening, primarily across south-central Arizona,
with some thunderstorms becoming strong to severe. The primary
threats with any strong thunderstorms will be strong erratic
outflows, locally heavy rainfall, and frequent lightning which
could cause new fire starts. There will be up to a 50-70% chance
for outflow winds to exceed 35 mph and up to a 10% chance for
winds to exceed 58 mph today. Chances for strong thunderstorms
will be present once again Thursday afternoon/evening before
thunderstorm chances begin to decrease starting Friday and remain
confined to the higher terrain this weekend. Outside of any
convection, winds will follow typical upslope/downvalley patterns
with intermittent gusts around 15-20 mph during the afternoon.
Min RHs will mostly range from 15-25%, while Max RHs will mostly
range between 30-60%.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530-532.

     Blowing Dust Advisory until 11 PM MST this evening for AZZ550-
     551-553-554.

CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ560>570.

&&

DISCUSSION...Smith
PREVIOUS DISCUSSION...Salerno
AVIATION...Whittock/Young
FIRE WEATHER...Smith/Salerno

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Preliminary Local Storm Report
National Weather Service Phoenix AZ
540 PM MST Wed Jul 24 2024

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

0331 PM     Tstm Wnd Dmg     4 E Desert Center       33.70N 115.33W
07/24/2024                   Riverside          CA   Law Enforcement

            Semi-truck was flipped by strong wind gusts
            and was blocking most of the EB lanes
            causing traffic to back up.

&&

Special Weather Statement
National Weather Service Phoenix AZ
630 PM MST Wed Jul 24 2024

AZZ553-250200-
Northwest Pinal County AZ-
630 PM MST Wed Jul 24 2024

...A STRONG THUNDERSTORM WILL IMPACT PINAL COUNTY THROUGH 700 PM
MST...

At 629 PM MST, Doppler radar was tracking a strong thunderstorm near
Coolidge Airport, or 9 miles south of Florence. This thunderstorm was
nearly stationary.

Strong, gusty winds will be capable of producing areas of blowing
dust with reduced visibilities below 3 miles.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

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

Locations impacted include...
Florence, Coolidge, La Palma, Randolph, Coolidge Airport, and Valley
Farms.

This includes the following highways...
AZ Route 87 between mile markers 123 and 137.
AZ Route 79 between mile markers 129 and 133.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MST for
southeastern Arizona.

&&

LAT...LON 3301 11157 3303 11127 3302 11127 3300 11130
      3281 11155
TIME...MOT...LOC 0129Z 002DEG 3KT 3290 11136

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

SDB

Special Weather Statement
National Weather Service Phoenix AZ
659 PM MST Wed Jul 24 2024

AZZ534-537-538-250230-
Aguila Valley AZ-Tonopah Desert AZ-Northwest Valley AZ-
659 PM MST Wed Jul 24 2024

...A STRONG THUNDERSTORM WILL IMPACT MARICOPA COUNTY THROUGH 730 PM
MST...

At 659 PM MST, Doppler radar was tracking a strong thunderstorm 14
miles northwest of Buckeye. This thunderstorm was nearly stationary.

Strong, gusty winds will be capable of producing areas of blowing
dust with reduced visibilities below 5 miles.

HAZARD...Wind gusts up to 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...
Buckeye.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MST for
south central Arizona.

&&

LAT...LON 3371 11290 3376 11271 3363 11259 3354 11289
TIME...MOT...LOC 0159Z 345DEG 2KT 3367 11278

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

SDB

Special Weather Statement
National Weather Service Phoenix AZ
736 PM MST Wed Jul 24 2024

AZZ553-250315-
Northwest Pinal County AZ-
736 PM MST Wed Jul 24 2024

...A STRONG THUNDERSTORM WILL IMPACT PINAL COUNTY THROUGH 815 PM
MST...

At 735 PM MST, Doppler radar was tracking a strong thunderstorm over
Randolph, or over Coolidge. This thunderstorm was nearly stationary.

Strong, gusty winds will be capable of producing areas of blowing
dust with reduced visibilities below 3 miles.

HAZARD...Wind gusts up to 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...
Casa Grande, Florence, Coolidge, Arizona City, La Palma, Blackwater,
Toltec, Arizola, Randolph, Coolidge Airport, and Valley Farms.

This includes the following highways...
AZ Interstate 10 between mile markers 186 and 204.
AZ Interstate 8 between mile markers 174 and 178.
AZ Route 87 between mile markers 124 and 146.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MST for
southeastern Arizona.

&&

LAT...LON 3277 11175 3276 11177 3307 11174 3304 11135
      3297 11134 3290 11145 3276 11162 3273 11169
      3273 11174
TIME...MOT...LOC 0235Z 000DEG 1KT 3295 11154

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

SDB