Phoenix, Arizona Weather Forecast Discussion

401
FXUS65 KPSR 281716
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1016 AM MST Sun Sep 28 2025
.UPDATE...Updated 18Z Aviation Discussion.
&&
.KEY MESSAGES...
- Isolated to widely scattered showers and thunderstorms will be
  possible this afternoon, mainly over the predominant terrain
  features of southwestern and southcentral AZ.
- A drier and much quieter weather pattern will settle into the
  region beginning on Monday and persist through this week.
- Temperatures will remain below normal today with gradual warm up
  to more seasonable temperatures by the middle of this week.
&&
.SHORT TERM /TODAY THROUGH MONDAY/...
Latest GOES-18 wv imagery and 500 mb streamline analysis reveals
a deep cutoff low which has been positioned near the Lower CO
River Valley over the past several days. This low has been
responsible for bringing our region multiple rounds of showers and
thunderstorms and heavy rainfall over the past few days.
Deterministic and ensemble guidance indicates the low pressure
system will finally weaken and lift into N AZ by this afternoon.
Although much less shower and thunderstorm activity is anticipated
today, latest HREF and REFS ensemble members do indicate there will
be enough residual moisture (PWATs of 1.2"-1.4") and instability (MU
CAPE of 500-1000 J/kg) in place across the lower deserts for at
least a few isolated to widely scattered storms this afternoon. The
most likely location for any convective development will be over the
high terrain features of southwest AZ including the Kofa Mountains
and extending farther N into La Paz and W Maricopa County. Rain
chances will be 10% or less for the Phoenix Metro this afternoon. As
negative 500 mb hght anomalies continue to overspread Arizona today,
we will see another afternoon with below normal temperatures. Highs
are expected to range from the mid 80s to around 90 degrees across
the lower deserts which is about 5 degrees below average for late
September.
On Monday, the upper-lvl low will transition into an open wave
and finally exit the Desert Southwest with a quasi-zonal pattern
becoming established. As this occurs, much drier air will arrive
into the region with PWAT values quickly falling below 1.00"
across the lower deserts. There are virtually zero rain chances
for the entire forecast area on Monday with mostly clear skies
expected. Highs will warm by a few degrees Monday afternoon,
mainly reaching the low to mid 90s across the lower deserts.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
A benign and dry weather pattern will take shape through the
middle of this week as ridging aloft begins to build over the
forecast area. 500 mb hghts will gradually increase to around
588-590 dam by the end of the week resulting in highs across the
lower deserts increasing from the mid 90s on Tuesday to the upper
90s to around 100 degrees on Thursday and Friday. Global models do
indicate a shortwave trough diving into the Intermountain West by
next weekend which may result in a slight cool down and breezier
conditions region-wide. Due to the trajectory of this system
remaining well north of the area, dry conditions are expected to
persist across the Desert Southwest.
&&
.AVIATION...Updated at 1715Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are expected during the TAF period. Winds
will resume following diurnal trends with speeds remaining
generally less than 10 kts. FEW clouds with lowest bases around
7-8k ft will be present through sunset before clear skies take
over.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected during the next 24 hours. Winds
will follow light and diurnal trends, with extended periods of
variability. Other than a FEW afternoon CU, skies will be mostly
clear
&&
.FIRE WEATHER...
Temperatures will remain below normal today followed by a gradual
warming trend through the beginning of this week. A low pressure
system is expected to lift into northern Arizona today where the
best chances for wetting rainfall will reside. Isolated showers and
thunderstorms will still be possible over the high terrain of
southwestern and southcentral AZ this afternoon. Rain chances will
come to an end across the area by this evening. MinRHs will range
from 30-45% this afternoon, falling to around 25-35% on Monday.
Overnight recovery will remain fair to good.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...Salerno
LONG TERM...Salerno
AVIATION...RW
FIRE WEATHER...Salerno

NWS PSR Office Area Forecast Discussion