380
FXUS65 KPSR 261126
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
426 AM MST Sat Sep 26 2026

.UPDATE...Updated 12Z Aviation Discussion.

&&

.KEY MESSAGES...

- For tonight into Sunday, higher level moisture will surge back
  into the region with skies becoming cloudy and eventual chances
  for light rain later in the day on Sunday.

- Rain is likely across much of Arizona on Monday and Tuesday with
  the possibility of some strong to severe thunderstorms. Moderate
  to heavy rainfall will also be possible, particularly across
  the Arizona high terrain.

- Temperatures will cool to below normal during the first half of
  next week with highs only in the eighties for much of the lower
  deserts.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
The main forecast concern continues to be the potential for strong
to severe storms, heavy rainfall, and flash flooding early next
week.

However, in the short term quiet weather conditions will continue
today as westerly flow persists. Expect mostly sunny skies today
with a slight uptick in temperatures as afternoon highs top out in
the upper 90s in the Phoenix area to the lower 100s across the
western lower deserts.

This will all begin to change tonight into Sunday as upper level
moisture gets peeled away from the decaying TC Odalys and advected
into our region. We should expect higher level clouds
overspreading the area from the southwest starting this evening,
gradually thickening up tonight with cloud bases dropping more
into the mid levels Sunday morning. The moisture advection will be
aided by a Pacific trough which is forecast to dive southeastward
toward the northern California coast on Sunday. There is still
some question for rain chances on Sunday as considerable dry air
will still be present in the lower levels. We do expect this
stream of moisture to last long enough to result in decent top
down saturation with light rain eventually reaching the surface,
but only in narrow bands. PoPs gradually increase from 10-15%
chances Sunday afternoon to 30-40% after midnight Sunday night.
Most areas that do see measurable rainfall on Sunday should stay
under 0.05". Daytime highs Sunday will also be held down due to
the cloudy skies with NBM forecast highs mostly in the mid 90s,
but it would not be surprising to struggle to make it past the
lower 90s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Model guidance is still pointing toward the potential for a
significant weather event occurring early next week as a strong
Pacific low pressure system moves into the region at the same time
moisture from TC Polo is forecast to advect northward into
Arizona. There have been some changes within the model runs over
the last 24 hours, noticeably with the low deepening further on
Monday and potentially becoming a slow moving closed low for
Tuesday into early Wednesday. The latest NHC track of Polo still
keeps it well to our south and southeast with its eventual remnant
circulation missing Arizona. However, it is still expected to
heavily influence our low and mid level moisture which will be one
of the key ingredients needed for a big rainfall event.

Model clusters heavily favor a closed low forming to our northwest
going into Monday with further strengthening possible as it moves
into our region on Tuesday. This deepening would result in a
slower moving system which has pushed back the timing of the best
rain chances, now most likely occurring late Monday night and/or
on Tuesday. Scattered showers and isolated thunderstorms are still
expected during the first half of Monday, but they should favor
the central and eastern Arizona high terrain. Pockets of moderate
rainfall will also be possible Monday, but the heavy rainfall
threat seems to have pushed back to Monday night and Tuesday. WPC
still maintains a Slight Risk for excessive rainfall for Monday
and Monday night for most of Arizona, minus the southwestern
portion.

Assuming no big changes with the timing and the strength of the
low, Tuesday now looks to hold our best chances for widespread
rainfall, likely moderate to heavy at times, and potentially a few
discrete severe thunderstorms. As the Pacific low slowly moves
into our region, strong 35-55 kt mid level south to southwesterly
flow will support very good upslope forced ascent into central and
eastern Arizona. At the same time, we are expecting to fall under
strong difluence aloft from as early as Monday evening through
Tuesday evening. One of the more uncertain ingredients for the
severe storm potential is the amount of instability that will be
available. Although model guidance suggests CAPE will struggle to
top 500 J/kg, it seems very possible a narrow corridor of better
instability closer to 1000 J/kg may develop later on Tuesday. If
all the ingredients come together, a few severe storms producing
damaging winds and large hail will be possible.

The latest QPF amounts have risen over the south-central Arizona
lower deserts with average amounts closer to 1.0" in the Phoenix
area to anywhere from 0.15-0.5" across the western lower deserts.
The highest storm total rainfall amounts are expected over the
high terrain north and east of Phoenix with current forecast
average amounts of 1-2". Locally higher amounts will occur due to
training of showers and storms with some areas potentially
reaching 3" for the two day period. The latest NBM guidance shows
probabilities of 2" as high as 55% for the higher terrain north
and east of Phoenix to 20% within Phoenix. NBM probabilities of
getting 3" of rainfall lower to 10-20% for higher terrain areas.
We will have to wait and see if these rainfall probabilities hold,
although even at this point it seems quite likely Flood Watches
will be needed for later Monday and Tuesday.

Due to the likely deeper and slower progression of the Pacific
low, rain chances now extend through Tuesday night for the eastern
half of Arizona and we anticipate PoPs to increase on Wednesday
if the timing holds. Any rainfall Tuesday night and Wednesday
should be more scattered, but we can`t rule out a few
thunderstorms producing additional localized moderate rainfall.
If the cold core of the low hangs out over our area into Wednesday
afternoon, we could easily see some afternoon storms that produce
small hail. For the western portions of our area on Wednesday,
drier air is expected to quickly move in leaving clearing skies
and quiet conditions.

Temperatures during the first part of next week will definitely
cool off with highs falling into the 80s for the south-central
Arizona lower deserts to the upper 80s and lower 90s for the
western lower deserts. After the Pacific low finally ejects to the
east late week, upper level ridging is favored to move in from the
west leading to gradual warming with highs potentially reaching
100 degrees again by next weekend.

&&

.AVIATION...Updated at 1125Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns are expected through the forecast
period. Winds will follow light and diurnal trends with some
variability prior to directional shifts. A period of southerly
crosswinds (150v200) is also anticipated at KPHX and KDVT late
this morning/early afternoon prior to the westerly shift. High
clouds will gradually increase in coverage through tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected during the next 24 hours. Winds
will fluctuate between westerly and southeasterly at KIPL and
southerly to southwesterly at KBLH. Wind speeds at both terminals
will remain aob 10 kt. Gradually increasing high clouds can be
expected through this morning with mid level cloud decks starting
to move into the region late in the period.

&&

.FIRE WEATHER...
Dry conditions will prevail today before higher level moisture
moves in on Sunday resulting in chances for mostly light rain.
MinRHs today will bottom out today at 15-20% across the lower
deserts to 20-30% over the eastern Arizona high terrain. Slow
improvement in RHs is expected on Sunday before much higher
moisture levels move in on Monday as rain chances quickly
increase and expand. Winds will generally follow the typical
diurnal tendencies with limited to no afternoon gusts this
weekend. Rain and much cooler weather are expected for Monday and
Tuesday with heavy rainfall a decent possibility across the
eastern districts. Conditions should eventually dry out later
next week with temperatures returning to near normal.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Salerno
FIRE WEATHER...Kuhlman