379
FXUS65 KPSR 292050
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
150 PM MST Thu Oct 29 2026

.KEY MESSAGES...

- A Flood Watch remains in effect for portions of south-central
  and eastern Arizona for Friday.

- Showers and thunderstorms, some producing moderate to heavy
  rainfall, are expected on Friday centered over south-central
  Arizona. Localized rainfall amounts of 1 to 2 inches are likely.

- Sunday will again bring flooding concerns as additional rainfall
  amounts of 1 to 2 inches are expected from Phoenix and areas to
  the north and east of Phoenix.

- A Flood Watch has been issued for portions of south-central and
  eastern Arizona for Sunday.

&&

.SHORT TERM /Today through Friday/...
Today will be the last dry and calm weather day ahead of the next
couple of weather systems that will bring rainy weather starting
Friday and expected to last through the holiday weekend. A large
trough is currently positioned off the western coast, with a cut-
off low developing along the coast of Washington. Additionally, a
near climatological record strong west to east subtropical jet is
stretched from northeast Hawaii to just west of the Baja coast.
This jet will play a pivotal role in how much rainfall we can
expect over the next several days, especially on Sunday as it will
drive a strong atmospheric river into our region.

As mentioned the rest of today will continue to be quiet, with
increasing cloud coverage throughout the rest of the day as the
southwesterly flow aloft is already beginning to be advected into
the region ahead of the large scale trough over the west coast.
By Friday PWATs will be near 200-250% of normal, and while the
troughing feature will remain positioned off the west coast, a
shortwave will track through the Desert SW Friday afternoon. This
shortwave will aid in providing enough ascent for showers and
thunderstorms to develop starting as early as Friday morning.
Forecast soundings and the latest HREF guidance continue to point
towards good elevated instability developing across south-central
Arizona tonight into Friday, potentially leading to MUCAPEs of
over 1000 J/kg in a small corridor from central Pima County
through western Pinal into northern Maricopa Counties. Latest Hi-
res CAMs show show showers developing as early as 5-7AM however
activity is expected to be light early Friday morning. The main
window for widespread showers and thunderstorms won`t be until
late morning/ early afternoon, where a few severe storms will be
possible, as SPC did upgrade the region from general thunderstorms
to a Marginal risk for severe weather Friday for south-central
and southeastern AZ.

Storm totals Friday are forecasted to generally be between 0.5-1.00"
centered over and just northeast of Phoenix. However, localized
amounts of up to around 2" are definitely possible with any severe
or training storms. With the expected totals a Floor Watch remains
in effect for Maricopa County, portions of NW Pinal County starting
Friday morning, then expanding into Gila County by the late morning
hours.

Otherwise, temperatures today will be very similar to the last few
days with highs mostly in the mid 80s across the lower deserts,
despite the periods of thicker high clouds. The increased clouds and
the periods of rain on Friday should hold daytime highs to at most
75 degrees in the Phoenix area, while the western lower deserts will
only dip down to around 80 degrees for highs.

&&

.LONG TERM /Saturday through Wednesday/...
A short drying period will move in on Saturday, but higher level
moisture and clouds will be increasing throughout the day. We
can`t rule out a few light showers on Saturday, but with little to
no instability and drier air in the mid levels little if any
additional accumulating rainfall is expected through at least the
afternoon. Some guidance is showing shower activity to begin
already in the evening, but for most areas it should hold off
until after midnight.

Attention then turns toward one of our stronger Arv that can
affect the Desert Southwest moving in Saturday night and lasting
through much of Sunday. The AR will also coincide with a fairly
strong shortwave trough developing west of northern Baja on
Saturday before tracking right through the southern half of
Arizona during the daytime hours Sunday. This weather event is
shaping up to be a classic El Nino season AR event which would
normally occur from late December through February. All of the
ingredients for a prolonged moderate rainfall event look to be
there on Sunday with an impressive 18 hours of 35-50kt
southwesterly upslope H8-H7 flow and at least 12 hours of strong
jet forced ascent. These impressive forcing mechanisms will also
line up with record or near record moisture levels for this time
of year with PWATs rising to 300-350% of normal. Instability will
be lacking with MUCAPEs at most 200-300 J/kg, but the long
duration of the rain will make up for the lack of higher rainfall
rates.

We expect showers to blossom first over the high terrain northeast
of Phoenix sometime in the evening before filling in across most
of south-central Arizona around or just after midnight. Showers
will stay somewhat scattered through the overnight hours before
becoming widespread over much of Arizona by mid morning Sunday. As
the main shortwave begins to track through southern California
later Sunday morning, a fairly solid shield of light to moderate
rain should move through southern California and then through
Arizona Sunday afternoon. Upslope showers should persist over
portions of south-central Arizona into the high terrain into
Sunday evening, but the activity should be gradually winding down.

Expected rainfall rates on Sunday are not all that high, but rain
totals will add up over time as this event will last longer than
our typical weather events. Based on the record moisture levels,
strong forcing, but little instability rainfall rates will
generally be in the 0.1-0.2"/hr range in the Phoenix area to as
high as 0.2-0.3"/hr in the high terrain north and east of the
Phoenix area. Fairly steady light to moderate rainfall is expected
from just before sunrise through the afternoon in the
aforementioned areas with rainfall totals averaging 1-1.5" in
Phoenix to 2-3" over the higher terrain. Believe it our not, the
NBM is also suggesting the possibility (25%) of rainfall totals
over 2" in the Phoenix to as much as 3-4" in the high terrain.
Much lower rainfall totals of 0.25-0.5" are expected over the
lower deserts of southwest Arizona and southeast California due to
some rain-shadowing effects and the lack of upslope forcing.

Even if the average forecast rainfall totals come to fruition on
Sunday, the bulk of the rain will runoff as it will be falling on
already saturated soils. In turn another Flood Watch has been
issued for a large area of south-central AZ, and the eastern AZ
high terrain starting Sunday, into Monday morning. During this
time we anticipate the potential for many of the washes filling or
overflowing, and flooding in some of the larger creeks and rivers
as all of the expected rain works through the water basins.

Dry air will begin to filter into the region from the northwest
later on Sunday, overspreading the bulk of the area by Monday
morning. We may have some lingering showers across the eastern
1/3rd of Arizona Sunday night into Monday morning, but additional
rainfall amounts should be fairly light. The rest of Monday will
bring decreasing clouds as the drier air works into the region
while another follow-on shortwave trough moves southeastward into
northern New Mexico. Temperatures for both Sunday and Monday will
be fairly cool with highs as low as the lower 70s for the Phoenix
area to maybe the mid to upper 70s across the western lower
deserts. Upper level ridging is then forecast to mostly take over
across the Desert Southwest going into the middle part of next
week, but temperatures will be fairly slow to rise with readings
staying below normal.

&&

.AVIATION...Updated at 1755Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT;
No major aviation concerns are expected through Friday morning.
Winds will contain an S/SE`rly component through sunset before
attempting to switch out of the W. However, confidence in a
typical full W`rly shift has decreased, therefore, VRB conditions
have been introduced for this evening. E`rly flow will eventually
become reestablished during the early morning hours.

By around 12Z, SHRA/TSRA may start to pop across the region,
potentially moving to within the vicinity of the terminals by
around 14Z. Uncertainty remains regarding the timing, and even if
this activity will come to fruition, so the PROB30 group for KPHX
has been maintained, with additional PROB groups added for the
remaining sites. Main impacts will be gusty and erratic winds,
reduced surface VIS and CIGs as low as 5-6 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather impacts are expected over the next 24 hours.
After periods of VRB conditions, W`rly flow will be favored at
KIPL, while a S`rly component will be seen at KBLH with some
fluctuations between SSW and SE. SCT-BKN mid and high level cloud
decks will be common across the region in addition to FEW and
occasionally SCT lower bases around 4-7 kft.

&&

.FIRE WEATHER...
After another overall dry day today, unsettled weather conditions
are expected starting Friday. Showers and thunderstorms will
impact much of the eastern districts on Friday with heavy rainfall
likely in some areas. Minimum humidity levels today are between
20-40% before rising substantially starting Friday with widespread
45-65%. The unsettled weather and cooler temperatures will last
through the weekend with widespread rainfall on Sunday. Outside of
any thunderstorms, winds will remain on the lighter side through
the weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...     Flood Watch from Saturday evening through late Sunday night for
     AZZ534-537>563.

     Flood Watch from Friday morning through Friday afternoon for
     AZZ534-537>551-553>555-559.

     Flood Watch from Friday afternoon through Friday evening for
     AZZ552-556>558-560>563.

CA...None.
&&

$$

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