172
FXUS65 KPSR 140558
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1058 PM MST Wed Aug 13 2025

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Increasing moisture will result in better shower and thunderstorm
chances the next few days with gusty winds, blowing dust, and
lightning the greatest threats.

- Rainfall chances decrease substantially by early next week with
storms primarily relegated to higher terrain areas of central and
eastern Arizona.

- Temperatures will steadily retreat near the seasonal normal
through the weekend with readings rebounding back above normal by
the middle of next week.

&&

.SHORT TERM /Today through Thursday/...
Early afternoon objective analysis indicates a weakening H5 anti-
cyclone stationed over northern Arizona with enhanced easterly flow
across southern Arizona ahead of an inverted trough entering central
Sonora. While this is a classic early August synoptic pattern, the
poleward positioning of better quality moisture is still lacking
with only a narrow plume of 8-10 g/kg mixing ratios advancing into
south-central Arizona. More robust moisture remains situated further
south into Mexico where explosive convective development last night
incurred gravity waves, outflows, and a shallow Gulf surge. Some of
this shallow moisture advection into south-central Arizona will be
distributed through the boundary layer via mechanical mixing and
more aggressive outflows resulting in somewhat better potential
instability and thunderstorm chances this afternoon through Friday.

A very complex forecast exists over the next several days strongly
influenced by mesoscale features and convective processes (fairly
typical for mid-monsoon). All model suites forecast scattered
mountain convection this afternoon propagating southwest towards the
axis of greater instability/moisture and creating organized, deep
outflow boundaries surging into lower elevations. Convective
sustenance should be aided by favorable upper level divergence and
the northern vorticity extension of the aforementioned inverted
trough; and early afternoon satellite imagery is already indicative
of large scale ascent juxtaposed with depressed convective
inhibition. However, forecast soundings reflect lower elevation
thunderstorm limitations where a deep, single outflow boundary would
likely be insufficient to vertically displace moisture to saturation
and convective freedom with CinH around 50 J/kg. For this case, it
would likely take 2 colliding boundaries to spark more than an
isolated storm - which conceivably may occur in western Maricopa
County contingent on organized storms erupting over western Pima
County. Nevertheless, wide T/Td spread and DCape greater than 1700
J/kg across lower elevations should allow stronger, moist outflows
to be maintained despite the expectation of lesser convective
regeneration behind the boundary. Raw HREF output continues to
suggest odds of 35 mph wind gusts upwards of 30-50% descending into
lower elevations this evening which could result in localized areas
of dense blowing dust.

Overwhelming evidence among all HREF members indicates a MCV and/or
northward vorticity extension of the inverted trough slowly
migrating over the eastern CWA Thursday morning. The majority of
indicators point towards prolonged midlevel saturation and weak
ascent such that morning elevated showers seem a very reasonable
outcome. Unlike the past couple weeks where similar scenarios
resulted in primarily virga, ample moisture below the cloud bases
should support some light measurable rainfall. Perhaps the greater
impact from morning clouds/showers will partial thermodynamic
contamination along with inability to realize full instability later
in the afternoon. High resolution modeling supports this outcome
with little reflection in afternoon/evening storms entering lower
elevations (and even limited development over higher terrain),
rather focusing better opportunities late Thursday night/early
Thursday morning. Despite this excellent agreement, mandated NBM
POPs paint unexpectedly high values over areas that will likely be
convectively challenged. In fact over the next several days,
automated NBM POP output appears completely unrealistic and mostly
high biased requiring large collaborative adjustments by all
neighboring forecast offices.

&&

.LONG TERM /Friday through Wednesday/...
Guidance is still showing the best moisture Friday with low level
mixing ratios increasing to 10-12 g/kg, but as with Thursday the
amount of cloud cover may hinder our convective potential. The flow
pattern should also become more dominated by the trough to our west
as the subtropical ridge shifts even farther to the east over Kansas
and Oklahoma. Right now, guidance holds off any dry air advection
into our area until Friday night into Saturday, so unless things
change we should have ample moisture for shower and thunderstorm
activity on Friday. As a result, the NBM paints the highest PoPs for
our area Friday afternoon and evening. Even with the better
moisture, it is still far from being really juicy as there will
remain a good deal of dry air aloft. However, both the GFS and the
Euro show good (1000-1500 J/kg) MUCAPE for Friday afternoon likely
with the help of the cooler air aloft associated with the nearby
trough. We will have to keep an eye on the severe storm potential
for Friday.

Drier air is expected to spread across the region from west to east
beginning Saturday as the trough finally begins to push the moisture
to the east. We may be able to squeeze out a few showers and storms
on Saturday, but chances will mainly be confined to the eastern
Arizona high terrain. By Sunday, conditions should be dry enough to
eliminate any chances over the lower deserts with at most 10-20%
PoPs over eastern Arizona. Similar low rain chances are expected for
Monday before we potentially see some moisture beginning to return
by next Tuesday or Wednesday.

Cooling temperatures will also be seen across the region later this
week as the trough lowers heights, moisture increases, and cloud
cover becomes a factor. NBM guidance shows highs dropping to between
102-106 degrees across the lower deserts by Friday. These near
normal temperatures may persist into Sunday before we start to warm
again early next week.

&&

.AVIATION...Updated at 0555Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The greatest weather concern will be low confidence on the wind
forecast Thursday evening, as it will be dependent on where
thunderstorm development occurs across the region and if any
organized outflows move through. Winds have been gusty and erratic
due to nearby thunderstorms this evening, but should eventually
settle out of the southeast within the next few hours. A period of
virga/light spotty showers remains possible tomorrow morning and
is reflected with VCSH in the TAFs. Winds will shift southwest by
late morning. By Thursday evening, confidence is low in whether
there will be enough thunderstorm development to the south and
east that we will see an organized outflow move across the
terminals, and latest Hi- Res guidance indicates some
thunderstorms could form within the Greater Phoenix Area (chances
around 25%) mid to late evening, likely dependent on a strong
enough outflow to trigger convection. Occasional VFR CIGs mainly
AOA 10 kft AGL will persist.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Thursday evening under
mostly clear skies. Winds will follow a near persistence forecast
with directions varying between SE and SW and gusts around 25kt
common at KBLH.

&&

.FIRE WEATHER...
A more active monsoon weather pattern is expected over the next few
days as moisture increases and temperatures begin to cool. Storm
activity today should be more concentrated over the Arizona higher
terrain, but there should also be some isolated evening storms and
gusty outflow winds into the lower deserts. Better moisture for
Thursday and Friday will result in continued rain chances across
much of the eastern districts with wetting rainfall chances as high
as 30-40% for the eastern districts. Minimum afternoon humidity
levels will mostly range between 15-25% with fair to good overnight
recoveries. Outside areas of thunderstorms, winds will continue to
follow diurnal trends with afternoon gusts up to 15-20 mph. Drier
air will eventually usher back into the area over the weekend mostly
ending rain chances except for far eastern Arizona. MinRHs will
eventually lower to closer to 10-15% by next Monday.

&&

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

$$

SHORT TERM...18
LONG TERM...Kuhlman
AVIATION...Whittock
FIRE WEATHER...Kuhlman