843
FXUS65 KPSR 222355
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
455 PM MST Fri Aug 22 2025

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

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

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

- Marginal risk for a few stronger thunderstorms capable of
  producing damaging winds through this evening, primarily east of
  the Lower Colorado River Valley.

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

&&

.SHORT TERM /Today through Sunday/...
A strong subtropical ridge of high pressure remains centered near
the Four Corners this afternoon, though beginning to gradually
weaken over the area. RAP analysis showed 500 mb heights remaining
around 594 dm, with the strong ridge of high pressure continuing to
promote well above normal temperatures across the region.
Temperatures so far this afternoon in Phoenix have already reached
112 degrees, which is one degree shy of the record high set back in
2011. Well above normal temperatures are expected to persist through
the weekend and will continue to promote widespread Major HeatRisk.
Temperatures will gradually trend downward this weekend as the ridge
gradually weakens, but daytime highs will continue to approach or
exceed 110 degrees each day. Meanwhile, morning lows across the
lower deserts will continue to remain in the mid to upper 80s to
around 90 degrees. However, one caveat that could influence
temperatures this weekend will be any monsoonal activity that could
help further cool us down. Despite some of this uncertainty, have
extended the Extreme Heat Warning for much of our area through
Sunday, so anyone with outdoor plans this weekend should be sure to
limit their time outdoors and drink plenty of water.

The position of the aforementioned subtropical high will continue to
be favorable for monsoonal activity across the region through the
weekend. Current radar shows much less thunderstorm activity along
the Mogollon Rim this afternoon compared to 24 hours ago, with quite
the active evening across the Valley yesterday. Latest CAMs continue
to show a lack of thunderstorm activity surviving into the south-
central Arizona lower deserts given yesterday`s monsoonal activity
working over the atmosphere. Anything that were to develop this
evening is expected to remain more isolated in nature, but would be
capable of producing strong outflow winds. Latest HREF shows
probabilities for outflow wind gusts in excess of 35 mph around 30-
50% across the Arizona the lower deserts, including southwest
portions of the state. HREF members continue to back off on the idea
of thunderstorm activity developing across southwest Arizona later
this evening with more uncertainty in whether or not strong outflows
will survive into this area. Nonetheless, any thunderstorms that
were to develop will be capable of strong outflow winds. Thus, SPC
has highlighted a good chunk of our area in a Marginal risk for
damaging winds, primarily east of the Lower Colorado River Valley.
Daily thunderstorm chances will continue through the weekend so stay
tuned for the latest updates.

&&

.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 2354Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary weather concern will be the potential for gusty
outflow winds and low confidence on VCSH/TS conditions this
evening under periods of SCT-BKN mid to high cloud decks. This
evening most likely direction of an initial outflow will be out of
the north, with gusts temporarily up to 25-30 kts. With only a
slight chance for SHRA/TSRA in the Phoenix airspace (15-25%
chances), VCSH between 02-06Z is noted in the TAF, and most CAMs
show thunderstorm activity favoring areas north and southwest of
the Phoenix area. Due to this activity confidence is low for wind
directions late this evening into the overnight hours. However
speeds should relax AOB 10 kts once again and eventually resume
diurnal tendencies, with a light E/SE switch by tomorrow morning
and returning to W by midday.


Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation concern will be the slight chance of VCSH/TS at
both terminals between 08-11Z under SCT-BKN mid to high clouds. 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. Daily thunderstorm chances will continue through the
weekend with monsoonal activity expected to expand to include the
western districts. Lightning, locally heavy rainfall, and gusty
erratic outflow winds will be the primary threats with
thunderstorms. Chances for seeing outflows in excess of 35 mph
through tonight will be around 30-50% east of the Lower Colorado
River Valley with more of this focused across southwest Arizona.
MinRHs will be around 15-25% through the weekend, while Max RHs
will be around 40-50% for most areas. Shower and storm chances
increase even more during the first half of next week. MinRHs will
be around 15-25% through the weekend, improving to 20-40% during
the first part of next week. 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 Sunday for AZZ530>555-559.

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

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

&&

$$

SHORT TERM...Smith
LONG TERM...Berislavich
AVIATION...Whittock/Ryan
FIRE WEATHER...Smith/Berislavich
CLIMATE...18