531
FXUS65 KPSR 221039
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
339 AM MST Fri Aug 22 2025

.KEY MESSAGES...

- Well above normal temperatures persist through the weekend,
  resulting in widespread areas of Major to locally Extreme
  HeatRisk.

- Extreme Heat Warnings continue across the majority of the region
  through the weekend.

- Strong to severe thunderstorms are possible across south-central
  Arizona, southwest Arizona, and the Lower Colorado River
  Valley, with the main threat being strong outflow winds.

- Better rain chances move into the region during the first half
  of next week.

&&

.SHORT TERM /Today through Sunday/...
The overall synoptic pattern has started to finally shift as of
early this morning. The subtropical high pressure has weakened
slightly (594 dm) and has shifted westward across southern Utah.
The high pressure is expected to remain in this general region
through the weekend with the strength of it largely fluctuating
around 593-595 dm. With the slight weakening of the high,
afternoon high temperatures will also slightly decrease.
Forecasted high temperatures will be in the 106-113 degree range
through the weekend across the lower deserts. Across the higher
terrain areas, highs will be in the 98-106 degree range today and
cool to 95-103 degrees this weekend due to the high shifting
westward. Morning low temperatures will remain in the mid 80s to
low 90s through the weekend across the lower deserts as well.
Morning lows may also end up being warmer than currently
forecasted depending on any residual cloud cover from thunderstorm
activity from the previous day. With the combination of these
temperatures, Major HeatRisk, with areas of localized Extreme
HeatRisk, will remain widespread across much of the region today
and through the weekend. Although this weekend the HeatRisk
decreases to moderate across the higher terrain. Due to this the
Extreme Heat Warning remains in effect through this weekend for
portions of the region. Today`s Extreme Warning includes the lower
deserts and higher terrain areas, tomorrow`s Extreme Heat Warning
is just across the lower deserts, and Sunday`s Extreme Heat
Warning is just the greater Phoenix Metro. However, Sunday`s may
need to be expanded across the rest of the lower deserts. Everyone
should continue to follow the proper heat safety precautions,
including limiting time outdoors and staying hydrated, to avoid
heat- related issues.

Even with the westward shift of the high pressure system, it remain
a favorable pattern for monsoon activity across our area. It
actually increases monsoonal across the western deserts. Favorable
easterly steering flow, of 15-20 kt. remains in place. Hi-res models
consistently show scattered showers and storms firing up this
afternoon in the higher terrain, both north and south of Phoenix,
and pushing into the lower deserts this evening. The models do
differ on the exact placement and coverage of these storms.
However, the environment is favorable for isolated to scattered
showers and storms to survive into the lower deserts. However,
there are some areas, particularly around the Phoenix Metro, that
are worked over from last nights storms. So these areas may not
see much, if any activity, tonight. Paintball plots support this
by showing activity skipping around the Phoenix Metro and
congealing in the deserts of southwestern AZ. The environment
will once again support strong to severe storms tonight, and the
SPC has placed south-central AZ, southwestern AZ, and the Lower
Colorado River Valley in a marginal risk for severe storms today,
with the main threat being severe winds (>58 mph). PWATs early
this morning are around 1.3-1.5" and are expected to increase to
around 1.5-1.7" later today. Forecast soundings also show MUCAPE
values greater than 1000 J/kg and DCAPE values around 1500-2000
J/kg, which further support the potential for severe storms. The
HREF shows a 30-50% chance of winds greater than 35 mph across
south- central Arizona, southwest Arizona, and the Lower Colorado
River Valley. The HREF also shows a bullseye in the lower deserts
of southwestern Arizona, where there is a 10% chance of winds
greater than 58 mph. These strong winds will be capable of
generating areas of blowing dust, and a Blowing Dust Advisory may
need to be issued later this morning.

With the overall synoptic pattern largely remaining unchanged
through the weekend, and easterly steering flow in place, it will
promote the continuation of daily thunderstorm chances across the
region. CAMs show similar patterns for shower and storm activity
over the next two days as is expected tonight (storms developing
in the higher terrain of Arizona and moving into the lower
deserts). However, each day`s activity will rely heavily on how
the previous day turns out. Either way, the main threats will be
strong gusty winds (main threat), excessive lightning and
localized heavy downpours (leading to localized flooding
concerns). The HREF does show a 30-50% chance of winds greater
than 35 mph for tomorrow.

&&

.LONG TERM /Monday through Thursday/...
Ensembles continue to be in good agreement that by the beginning of
next week the overall synoptic pattern will shift, with the
subtropical high weakening and shifting to the south and east. This
shift will occur due to two troughs, one digging into the
east/north east portion of the US and another trough digging off
the Pacific coast. This will do a couple things for our region.
One it will shift the steering flow to be out of the
south/southeast, which will promote better moisture into our
region. And two, the weakening of the high will lead to cooling
temperatures.

As for the changing steering flow and increase in moisture, that
will bring better chances for showers and storms across much of the
area for the first half of the workweek. So, we may see more
scattered to potentially widespread activity. The ensembles do still
disagree on the amount of moisture that will move into our region.
The GEFS keeps PWATs in the 1.5-1.6" range, whereas the ECMWF
ensemble increases PWATs to the 1.7-1.9" range. Due to this, the
ECMWF does have better PoPs across our region than the GEFS.
Either way should be ample moisture to at least produce isolated
to scattered activity across portions of the CWA. The NBM was
running hot still, so did lower those slightly. Stay tuned for
updates as we get closer to next week.

As for the cooling temperatures, the weakening of the ridge and
lowering heights (588-592 dm) aloft within of itself will lead to
cooling temperatures. But showers and storms, and their
associated cloud cover, will also help to dampen temperatures.
Afternoon high temperatures are forecasted to cool to near to
slightly above normal on Monday, with temperatures falling below
normal for the middle of the workweek (Tuesday-Thursday).
Forecasted high temperatures range from 104-109 degrees on Monday
and 94-102 degrees Tuesday-Thursday across the lower deserts.
Morning lows are also expected to fall back to near normal and are
forecasted to range from the upper 70s to mid 80s. With the
cooling temperatures we will also see HeatRisk decreasing,
becoming widespread moderate on Monday and widespread minor
Tuesday-Thursday. While models are in good agreement on the
overall pattern for the beginning of the week, they start to
differ, quite a bit, by the middle of the week. This discrepancy
is mainly driven by the aforementioned trough off the Pacific
coast and how far south it will dig and how far inland it might
push. This discrepancy can be seen in the IQR temperature scores.
The maxT IQR scores are 6 for Tuesday, 10 for Wednesday, and 12
for Thursday. Either way, increasing storm chances and cooling
temperatures are expected for the first half of next week.

&&

.AVIATION...Updated at 0558Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light rain showers/virga remains overspread the Phoenix area
tonight, with some lingering dust that is creating lowered
visibilities under 10 miles. The showers/virga is expected to
clear up by 9-10Z tonight and the dust should slowly settle over
the next couple hours. Several weak outflows are still moving
through the Phoenix area. This and the weak showers will continue
to create erratic winds and a low confidence wind forecast through
Friday morning, but speeds should remain light, < 8 kts, through
the rest of the night. Afternoon thunderstorms Friday are expected
to focus well north, south, and west of the Phoenix terminals.
However, outflow boundaries from this activity may lead to
isolated convection Friday night. This is reflected with a PROB30
-SHRA with the 06Z TAF package.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Friday under passing
mid/high cloud decks. Wind trends will be similar to the past 24
hours with directions generally varying between SE and SW. Periods
of variability or nearly calm conditions will be common during
the morning hours.

&&

.FIRE WEATHER...
Temperatures will remain around 4-7 degrees above normal through
the weekend, cool to near normal on Monday, and cool below normal
for the middle of next week. The overall pattern for storms
through the weekend will be relatively similar, with scattered
showers developing across the higher terrain during the afternoon
and pushing into the lower deserts during the evening. Each day`s
activity will depend on how the previous day shakes out. The main
threats with these storms will be strong, gusty winds (main
threat), excessive lightning, and localized heavy downpours. HREF
probabilities, for today, show a 30-50% chance of winds exceeding
35 mph across south-central AZ, SW AZ, and the Lower CO River
Valley and a 10% chance of winds exceeding 58 mph over SW AZ.
Shower and storm chances increase even more during the first half
of next week. MinRHs will be around 15-20% through the weekend,
improving to 20-30% on Monday, and 25-40% Tuesday-Thursday.
Overnight recoveries will be fair through the weekend and good
during the first half of next week.

&&

.CLIMATE...

Record highs later this week:

Date       Phoenix          Yuma          El Centro
----       -------          ----          ---------
8/22     113 in 2011     115 in 1969     117 in 1969

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Saturday for AZZ530>536-538-
     539-541-545-547-549-552>555-559.

     Extreme Heat Warning until 8 PM MST Sunday for AZZ537-540-
     542>544-546-548-550-551.

     Extreme Heat Warning until 8 PM MST this evening for AZZ556-560-
     562.

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

&&

$$

SHORT TERM...Berislavich
LONG TERM...Berislavich
AVIATION...Benedict/Frieders
FIRE WEATHER...Berislavich
CLIMATE...18