560
FXUS65 KPSR 260508
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1008 PM MST Sun Oct 25 2026

.UPDATE...Updated 06z Aviation Discussion...

&&

.KEY MESSAGES...

- Temperatures for the upcoming week will generally be within the
  normal range for late October with lower desert highs mostly in
  the mid eighties.

- Dry and tranquil weather conditions will last through the middle
  of week.

- A return to inclement weather with increased rainfall chances is
  likely towards the end of the week.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
The center of the low continues to linger across Northern
Arizona, but behind the low, as is continues to track to the NE,
drier and warmer conditions are expected for the lower desert. On
the RAP40 500MB analysis ridging can already be seen building
over the coastline of southern CA and stretching into the Intermountain
West. However the increasing H5 heights will be somewhat
suppressed as another upper level low, currently positioned just
off the coast of Washington, will push inland starting early
Monday. This low is expected to stay in northern CONUS, and not
dive south towards the Desert SW, however as mentioned before this
will help suppress H5 height aloft from building over the lower
deserts, resulting in near normal heights for this time of year
and quasi-zonal westerly dry flow lasting through Wednesday.

With that being said temperatures will be in the low to mid 80s
today, then starting tomorrow increase to the mid to upper 80s,
lasting through Wednesday. NBM forecast highs do show readings
nudging more toward the upper 80s for Tuesday and Wednesday, but
there is currently only a 25% chance (for KPHX) at reaching 90
degrees this week. Meanwhile morning lows will be in the low to
mid 60s.

&&

.LONG TERM /THURSDAY THROUGH NEXT SUNDAY/...
Models continue to suggest a more organized large scale troughing
pattern setting up later this week with the parent low setting up
along the British Colombia coast before diving southward into the
Pacific Northwest by Thursday. A secondary shortwave or weak
closed low may also form west of California Wednesday into
Thursday, more associated with the sub-tropical jet. What is
likely to be more important is the eventual phasing of the polar
jet over the Pacific Northwest with the stronger subtropical jet
by next Friday. Both the EPS and GEFS support this phasing, while
also strengthening the subtropical jet to near record strength
for this time of year just west of Baja on Friday. Guidance then
supports a fairly strong weather system (with H5 heights within
the 10th percentile of climatology) developing within the base of
the trough by next weekend. Although we are at around 5-7 days
out from this next expected weather event, there is enough model
evidence for us to begin worrying about another significant
precipitation event. A bit more than 50% of the ensemble members
favor the trough deepening just off the West Coast Friday into
next weekend, likely pushing a modest to strong atmospheric river
(AR) somewhere into the Southwestern U.S. next weekend.

As the trough first begins to set up during the middle part of the
week, there is high confidence in strong northward moisture
advection in the upper levels out of Mexico Wednesday night into
Thursday. This should be followed by lower level moisture
advection later Thursday into Friday. Although the timing may
change and assuming the positioning of the subtropical jet is
correct, shower chances may begin as early as late Thursday and
carry into Friday under broad divergence aloft and modest upslope
southerly flow. This first period of rain chances very well could
change and confidence is still quite low in how much rain could
fall.

Scattered mostly high terrain rain chances may continue into
Saturday before the main weather system traverses the region at
some point Saturday night and Sunday. Additional moisture
advection is likely to occur, associated with the AR, right ahead
of the weekend system, but it is too early to know where exactly
the best moisture and forcing will end up. Even if we do not get a
direct hit, ensemble guidance is heavily favoring at least a
partial hit from the AR late Saturday into Sunday. Preliminary QPF
numbers show upwards of an inch may be possible over the south-
central Arizona lower deserts to upwards of 2" possible in the
high terrain north and east of Phoenix. These numbers very well
could change and seem to lean more on the optimistic side. If the
upper end of precip guidance comes to fruition, locations across
central Arizona are expected to have to worry about rising stream
and river levels again, but it is doubtful there will be big
flood concern due to the longer duration of the event. Given we
are still outside the winter season, this weather system will be
on the warmer side with snow levels likely staying above 9-10K
feet.

&&

.AVIATION...Updated at 0505Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns expected throughout the TAF period.
The overall wind pattern will exhibit the typical diurnal
tendencies with overall speeds aob 7 kts along with extended
periods of light variability to even calm conditions. Mostly
clear skies will give way to some passing high clouds during the
day Monday.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns expected throughout the TAF period.
Wind speeds will generally be light aob 6 kts with a westerly
component favored at KIPL and a northwest to northeasterly
component favored at KBLH. Extended periods of light variability
to even calm conditions can be expected. Clear skies will give way
to some passing high clouds during the overnight and morning
hours.

&&

.FIRE WEATHER...
High pressure will settle back into the region over the next
couple of days leading to drier conditions and temperatures
returning into the normal range. Minimum humidity levels will
fall into a 20-40% range this afternoon and then 15-35% on
Monday. Overnight recoveries will remain good at 45-70% across the
area. Winds will remain light each day favoring typical diurnal
patterns. A shift in the weather pattern late this week and into
next weekend may bring about cooler, wetter, and breezier
conditions.

&&

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

$$

SHORT TERM...Ryan/Kuhlman
LONG TERM...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Kuhlman