613
FXUS65 KPSR 171836
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1005 AM MST Sun Aug 17 2025

UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- As high pressure returns to the region, temperatures will steadily
climb back above normal over the next few days with widespread major
HeatRisk becoming common later in the week.

- 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/...
Latest mid-lvl wv imagery and 500 mb streamline analysis reveals a
broad trough of low pressure overspreading the western CONUS while
a ridge of high pressure is located over the Southern Plains and
Midwestern states. Our forecast area remains centered between both
of these features under the influence of dry southwesterly flow
aloft. Heading through the today, we will continue to see dry and
tranquil weather conditions across the region as dew points remain
in the upper 40s to around 50F. Due to 500 mb hghts over the
forecast region remaining between 588-580 dam, temperatures will
again be right around seasonal norms this afternoon with highs
ranging from 100-105F across the lower deserts and mid to upper 90s
across the higher terrain of southcentral AZ. A drier boundary layer
and sufficient radiational cooling will allow lows to fall to the
upper 70s to mid 80s again tonight.

Heading into Monday, model guidance continues to show weakening of
the upper trough over the West Coast as the subtropical ridge
located over the S Plains retrogrades wwd into the Four Corner
region. This will cause winds in the mid lvls of the atmosphere to
shift from SW to SE and begin to advect moisture back into southern
portions of AZ. High-res models do show convection initiating over N
MX and SE AZ Monday afternoon, however chances for any outflow
boundaries reaching the lower deserts of southcentral AZ remains low
(<10%) at this time. As high pressure aloft begins to build, highs
Monday afternoon will top out slightly above normal around 102-107F
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 end of this week. An
Extreme Heat Watch will likely be issued in subsequent forecast
packages, mainly for the Wed-Fri time period.

GEFS and EPS member 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 1700Z.

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...None.
CA...None.

&&

$$

SHORT TERM...Salerno
LONG TERM...Salerno
AVIATION...18
FIRE WEATHER...Salerno
CLIMATE...18