042
FXUS65 KPSR 172328
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
428 PM MST Sun Aug 17 2025

.UPDATE...Updated 00z Aviation Discussion.

&&

.KEY MESSAGES...

- As high pressure returns to the region, temperatures will
  steadily climb back above normal during the upcoming week with
  widespread Major HeatRisk becoming common later in the week.

- With Major HeatRisk materializing, Extreme Heat Watches are in
  effect across the majority of the region Wednesday through
  Friday.

- Rainfall chances will remain confined to the high terrain of E
  and SE Arizona through the first half of this week before
  chances expand to the lower deserts by the end of the week.

&&

.SHORT TERM /Today through Monday/...
The latest water vapor satellite imagery depicts upper-level
troughing situated along the west coast with an elongated ridge
centered from the Southern Plains through the Ozarks. The area is
situated between these two features with a dry, southwesterly
flow aloft prevailing as PWATs have dropped below one inch. As a
result of this dry air mass in place, very quiet conditions are
expected for the rest of today across the forecast area with any
storm activity expected to be relegated across far southern AZ
where the deeper moisture resides. Under the influence of the
troughing feature off the west coast, afternoon high temperatures
today will continue to be near normal across south-central AZ to
slightly below normal across the western deserts as readings will
range between 100-105 degrees.

Heading into Monday, the overall synoptic pattern begins to shift as
the troughing feature along the west coast weakens and allows the
subtropical high to build westward to near the Four Corners
region. This pattern change will cause the overall wind flow to
shift from the southwest to southeast with moisture beginning to
increase somewhat across southern AZ. Storm activity Monday
afternoon/evening will once again be relegated across far southern
AZ through northern MX with the forecast area remaining dry as
moisture levels will remain quite limited. With the subtropical
high building near the Four Corners, heights aloft will slightly
increase with surface temperatures expected to climb a couple of
degrees as afternoon highs will range between 102-107 degrees
across the lower deserts.

&&

.LONG TERM /Tuesday through Saturday/...
The subtropical ridge will strengthen further heading into the
middle of this week as 500 mb hghts climb to around 596-598 dam over
the Four Corners region. The increase in hghts aloft will result in
a drastic spike in temperatures across the Desert Southwest,
boosting highs up to 110 in the lowest elevations on Tuesday and
above 110 degrees across much of the lower deserts starting on
Wednesday. Highs are also expected to reach near record levels by
Thursday and Friday, topping out around 113-115 degrees with
overnight/morning lows expected to remain very warm in the upper 80s
to low 90s. Consequently, HeatRisk values will rise from the
Moderate to fairly widespread Major by the latter portion of this
week and thus Extreme Heat Watches have been issued across the
majority of the region from Wednesday morning through Friday
evening.

GEFS and EPS members are in good agreement that mixing ratios
will increase to around 10 g/kg and PWATs rise to around 1.5"
beginning as early as Tuesday and persist through the end of this
week which will promote at least daily thunderstorm activity over
the high terrain surrounding Phoenix. There is at least a low
chance that storms could survive into the lower deserts by the
latter half of the week, but subsidence from the anomalously
strong ridge will likely keep storm coverage more limited. The NBM
is still carrying around 10% chances for lower desert storms
Tuesday and Wednesday before increasing to around 20-30% Thursday
through Saturday.

&&

.AVIATION...Updated at 2330Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Monday afternoon as
mostly clear skies today likely give way to some BKN midlevel decks
(and possible virga) Monday morning. W/SW wind directions should
predominate the major of the period with a later than usual switch
to the nocturnal easterly, and in some cases just becoming variable
or nearly calm during the morning hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
No weather issues will exist through Monday afternoon under clear
skies. Wind behavior will be nearly identical to the past 24 hours
as directions generally vary between SE and SW with limited
gustiness. Periods of nearly calm conditions will be common around
sunrise.

&&

.FIRE WEATHER...
Temperatures will increase from near normal to well above normal
by the middle of this week. Winds will continue to follow diurnal
patterns with some afternoon gusts in the 15-20 mph range. Relative
humidity will bottom out around 15-25% across the eastern districts
and 10-20% across the western districts each afternoon. Overnight
recovery will range from poor to fair. Thunderstorm activity will
likely remain confined to the higher terrain of E and SE AZ through
the first half of this week before expanding to the lower deserts
later in the week. Chances for wetting rainfall will remain 20% or
less for the foothills of Maricopa and S Gila County through the end
of this week.

&&

.CLIMATE...

Record highs later this week:

Date       Phoenix          Yuma          El Centro
----       -------          ----          ---------
8/20     113 in 2019     114 in 1982     114 in 1969
8/21     114 in 2019     115 in 1969     117 in 1969
8/22     113 in 2011     115 in 1969     117 in 1969

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Watch from Wednesday morning through Friday evening
     for AZZ530>556-559-560-562.

CA...Extreme Heat Watch from Wednesday morning through Friday evening
     for CAZ560>570.

&&

$$

SHORT TERM...Lojero
LONG TERM...Salerno/Lojero
AVIATION...Young/18
FIRE WEATHER...Salerno
CLIMATE...18