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