980
FXUS65 KPSR 241211
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
511 AM MST Fri Jul 24 2026

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Much above normal temperatures will continue through the
  weekend with readings approaching near record levels and Extreme
  Heat Warnings in effect.

- The high pressure system responsible for the extreme heat will
  also restrict thunderstorm development with minimal chances
  today.

- Temperatures will cool slightly early next week as increased
  thunderstorm coverage returns to the region.

&&

.SHORT TERM /Today through Sunday/...
A sprawling subtropical high pressure system was covering the
southern Conus early this morning with one 597dm H5 center over
southern New Mexico. The overall trend in the anti-cyclone center
is towards a retrogressive phase, however this will change over
the next 48 hours with the core lifting towards central Colorado.
Despite this movement, the forecast area will maintain H5 heights
in a 596-598dm range with H8 and H7 temperatures well above +30C
and +15C respectively which are general proxies for lower
elevation temperatures reaching/exceeding 110F. Numerical guidance
spread has narrowed recently providing increased confidence of
many lower elevation communities touching 115F today and Saturday
yielding widespread major and areas of extreme HeatRisk.
Confidence in forecast temperatures deteriorates significantly
Sunday as strong, moist thunderstorm outflows Saturday night may
substantially alter boundary layer moisture and mixing depths, as
well as introducing pesky midlevel cloud decks detrimental to
daytime insolation. This outcome is reflected in numerical
guidance where the full range in ensemble spread widens, but also
abruptly drops from the Friday/Saturday levels.

As the center of the subtropical ridge shifts into Colorado, this
will allow better easterly flow to develop on the southern
periphery of the anti-cyclone over northern Mexico/southern
Arizona. Subsidence and somewhat drier air will be maintained
today over the CWA in proximity to the high pressure center.
However much like yesterday, this will not completely preclude
deep convective development over the most favored mountain
locations, though this activity should be very isolated and short-
lived in nature. This will gradually change over the weekend as a
well defined easterly wave/inverted trough comprised of tropical
remnants crosses into northern Mexico.

Confidence is growing that the northern extent of the inverted
trough and jet streak will cross into southern Arizona Saturday
afternoon providing a very convectively favorable difluent flow
aloft. While mixing ratios languishing under 10 g/kg and a warm
midlevel thermal layer should preclude storm development over most
lower elevation locations, DCape values 1500-2000 J/kg will
promote strong, long lived outflow boundaries racing into lower
deserts creating elevated chances of dense blowing dust (primarily
over Pinal County). This outflow will also enhance and deepen the
moisture pool bringing boundary layer mixing ratios back into a
11- 12 g/kg range and spiking total column PWATs near 1.75".
Surprisingly, models are not overly enthusiastic regarding more
expansive thunderstorm development Sunday with a continuation of a
favorable synoptic pattern, MLCape exceeding 1000 J/kg, and DCape
still near 1500 J/kg. Forecast BUFR soundings suggest lower
elevation CinH in excess of 25 J/kg, though multiple colliding
outflows should conceivably breach this inhibition suggesting
there may be other factors contributing to models not producing
better storm chances.

&&

.LONG TERM /Monday through Thursday/...
Strong, expansive ridging will remain nearly in place next week
across the southwest and central United States with the anti-
cyclone center rotating back from central Colorado into New Mexico
and Arizona. Early in the week, sufficient easterly flow will
prevail over the region juxtaposed with marginally supportive
mixing ratios of 9-11 g/kg for scattered storms. There remains
considerable uncertainty regarding a more preferred time frame for
higher POPS in any given location with mesoscale details likely
becoming more important towards convective evolution.
Unfortunately, the mandated NBM/WPC forecast during this time only
further complicates and diminishes the forecast confidence with
numerous instances of spurious QPF forcing procedural, un-
scientific higher POPs spread over uncommon time periods based on
climatology and the preponderance of trusted model output. In
reality, this appears to be a very typical monsoon pattern with
alternating convectively active and inactive days. By the latter
half of the week, there are a handful of NAEFS members indicating
notable strengthening of the high pressure with 600dm H5 heights
materializing over northern AZ/southern UT. It appears the NBM/WPC
forecasts are latching onto this scenario as POPs dwindle to much
lower than expected values given the ensemble mean synoptic
pattern. The larger impact of this outcome would be a return to
major HeatRisk and extreme heat thresholds towards the end of the
week.

&&

.AVIATION...Updated at 1210Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No significant aviation weather impacts are expected through
Saturday morning, with FEW to SCT mid and high clouds. There is
notable forecast uncertainty with the wind directions through the
TAF period. Winds are slowly coming around to the E this morning.
A few hours of light VRB may precede diurnal W`rlies between
16-21Z. Winds are expected to favor typical diurnal trends heading
into tonight, but some guidance suggests a boundary will arrive
from the south at some point early Saturday morning and maintain
or shift winds back to the S-SW. Wind speeds through the TAf will
mostly stay below 10 kt, with afternoon gusts up to 15-20 kts.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather impacts expected through Saturday morning
under FEW mid and high level cloud decks. Wind directions will
generally fluctuate between the southeast to southwest. Some
elevated gusts upwards of 20-25 kts are likely this afternoon at
KBLH.

&&

.FIRE WEATHER...
Thunderstorm chances will remain low today with only a limited
opportunity remaining over high terrain areas in Arizona. Better
chances for more expansive storm coverage and wetting rainfall
will arrive later in the weekend and early next week with activity
focused over higher terrain locations. With temperatures hovering
much above normal and near record levels the next several days,
minimum afternoon humidity in a 10-25% range will improving closer
to a 20-30% range next week. Correspondingly, overnight recovery
will mostly be in a fair to good range of 30-60% with somewhat
higher values next week. Outside of thunderstorm outflows, wind
speeds should be fairly light through the period with only local
afternoon gusts 20-25 mph.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Monday for AZZ530>555-559.

     Extreme Heat Warning from 10 AM this morning to 8 PM MST
     Saturday for AZZ556-560>562.

CA...Extreme Heat Warning until 8 PM PDT Monday for CAZ560>570.

&&

$$

SHORT TERM...18
LONG TERM...18
AVIATION...Benedict/Lojero
FIRE WEATHER...18