153
FXUS65 KPSR 172306
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
406 PM MST Fri Oct 17 2025

.UPDATE...Updated 00Z Aviation Discussion.

&&

.KEY MESSAGES...

- Dry and tranquil weather conditions with zero rain chances will
  prevail through the weekend with temperatures gradually warming
  into the normal range.

- Temperatures will warm a bit further early next week with lower
  desert highs topping out around 90 degrees before cooling back
  into the normal range later in the week.

- A passing weather system during the middle of next week may
  bring some light shower activity focused over the Arizona high
  terrain.

&&

.SHORT TERM /TODAY THROUGH SATURDAY NIGHT/...
Current mid-level water vapor imagery depicts broad troughing
over the northern Rockies and Northern Plains, with a positively
tilted, elongated shortwave progressing through AZ. Upstream, a
few features also evident in water vapor imagery will begin to
influence the region during the forecast period: 1) upstream
ridging over the northeast Pacific and 2) an upper low, detached
from the northern stream and meandering off the Southern CA/Baja
Coast. For today, continued negative midlevel height anomalies
aloft (thanks to the shortwave progressing through the region)
will support below normal temperatures once again, with afternoon
highs in the lower to middle 80s across the typically warmer
lower desert locales. Additionally, enough moisture is present
ahead of the shortwave that fair weather cumulus have developed
over the AZ high terrain and Southeast AZ, which will linger
through the rest of the afternoon.

The shortwave overhead will quickly eject eastward tonight,
allowing midlevel heights to quickly build into the region from
the southeast. This process will be aided somewhat by the
progressive northern stream, as the northeast Pacific ridge
shifts over the northwest US. The cutoff low off the SoCal/Baja
Coast may also act to "pump" up midlevel heights downstream as it
meanders closer to the Coast tomorrow. Regardless, ensembles
agree that H5 heights will reach a 587-589 dam range by Saturday
night, supporting a warming trend to near normal temperatures
over weekend. Expect afternoon highs to warm solidly into the
middle 80s across the lower deserts tomorrow afternoon, just a
few degrees shy of daily averages.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
The latest model guidance  has shifted slightly toward higher
heights for Sunday through at least Tuesday as the developing cut-
off low is now shown to be a bit farther to the west off the coast
of Baja. These likely higher heights have bumped up the
temperature forecast for Sunday- Tuesday by two or three degrees
with the NBM now showing highs closer to or even reaching 90
degrees during the period. These forecast highs are still
basically within the normal range for this time of year. The dry
boundary layer conditions and clear to mostly clear skies will
continue to promote efficient nocturnal cooling with overnight
lows only rising into the upper 50s to mid 60s by early next week.

Modest forecast uncertainty remains for the eventual conclusion
of the cut-off low, but at least the GEFS and EPS are in better
agreement than last night. Both models show the cut-off low
beginning to weaken as it starts to make northeastward progress
toward southern California on Tuesday. They also show a very
similar track of bringing the low into southern California around
Tuesday night, but the GEFS weakens the system more quickly
showing an open wave before moving onshore. Both model suites also
agree on some modest southerly moisture advection into south-
central and southeastern Arizona at some point later Tuesday/early
Wednesday, but mean PWATs are only shown to reach 0.6-0.8" or
on the higher end of the climatological normals. Assuming no
major changes to the forecast of this cut-off low, any fairly
limited rain chances are likely to be focused over higher terrain
areas of south-central and eastern Arizona late Tuesday into
early Wednesday.

Temperatures should also retreat some as the system passes
through our region with NBM highs falling more into the mid 80s by
next Wednesday. Looking out a bit further, we should stay in a
dry westerly somewhat zonal flow going into next weekend. A
Pacific trough is forecast to move onshore somewhere across the
Pacific Northwest/California by next weekend, but for now guidance
favors this system mostly bypassing our region to the north.

&&

.AVIATION...Updated at 2305Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the TAF
period. Winds across the Phoenix area terminals will follow
diurnal tendencies with extended periods of light and variable to
at times calm conditions. Winds at KIPL will predominantly favor a
northerly component, with extended periods of variability, while
directions at KBLH vary between NNE and NW. Expect light winds
aob 7 kts through the period under mostly clear skies.

&&

.FIRE WEATHER...
Dry, tranquil weather with temperatures gradually warming into the
normal range will prevail through the weekend. Minimum afternoon
humidity levels will fall into a 15-25% range across the lower
deserts to upwards of 30-35% over the eastern Arizona high terrain
today before falling more into a 15-25% range areawide starting
Saturday. Overnight recovery will remain good to excellent. Light
diurnal winds are expected across the eastern districts, while
some occasional breezy northerly winds will be seen across the
western districts today. Near to slightly above normal
temperatures with MinRHs between 15-25% are forecast to continue
through early next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

SHORT TERM...Whittock
LONG TERM...Kuhlman
AVIATION...Berislavich/Smith
FIRE WEATHER...Kuhlman