577
FXUS65 KPSR 011131
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
431 AM MST Sun Nov 1 2026

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- An atmospheric river today will continue to bring widespread
  rain showers and isolated storms, leading to gradual rises in
  area washes, creeks, streams, and rivers in south-central
  Arizona.

- A Flood Watch is in effect for much of central and eastern
  Arizona through tonight.

- Isolated strong to severe thunderstorms will be possible this
  afternoon and evening, mostly east of the Colorado River, with
  the main threat being damaging winds.

- Conditions will quickly dry by daybreak Monday and remain dry
  through the week, along with daytime temperatures slowly warming
  closer to, albeit still below, daily normals during the middle
  of the week.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...

Is this the Desert Southwest of the Pacific Northwest?! The first
atmospheric river of the season is moving right into the region
and it is one of the strongest ARs, in terms of IVT, to hit the
Desert Southwest over the last decade. Satellite TPW around
midnight this morning showed the best subtropical moisture was
still just west of Baja California with a favorable trajectory to
work across the peninsula up into AZ. Ensemble guidance shows
this slug of moisture, with IVT magnitudes pushing 1000 kg/ms,
arriving in AZ by around 5 AM this morning and persisting with IVT
values >750 kg/ms through around noon-early-afternoon today. So,
this morning will likely be the timeframe when the bulk of the
widespread soaking rain will fall. Widespread rainfall amounts of
0.5-1.5" already fell Saturday evening/night across central AZ
and light to moderate rain was still falling early this morning
with measured hourly rates of around 0.05-0.25". There is strong
model consensus that rainfall totals the rest of Sunday will reach
0.50-1.50" or more across the lower deserts to in excess of
2.00-3.00" in the favored upslope terrain areas north and east of
Phoenix. Multiple ensembles even show high probabilities (>60%)
of exceeding 4.00" in the favored terrain. Rain totals across SE
CA and SW AZ will be on the lighter side, however localized totals
up to 0.50-1.00" are still possible with some banding. The rain
that has fallen over the past two has already resulted in rises in
area creeks, streams, rivers, and washes, and the Salt River
Project has been releasing water into the Verde and Salt River
systems. Runoff and rises is only going to continue through the
end of this weekend as rain adds up, with several waterways
forecast to exceed designated action stages and some that may even
exceed flood stages. Even after the rain is all done the runoff
may continue through the first half of this week.

While most of the rain will be stratiform and light to moderate in
nature through the morning, there will be chances for
thunderstorms as well, especially this afternoon behind the main
band of rain and there will even be a marginal severe wind threat
as the shortwave guiding the AR moves through central. Any storm
today will pose more of a flash flooding risk with higher rain
rates. The instability will be fairly low, CAPE values mostly
under 500 J/kg), and mid level lapse rates will be poor (<6 C/km).
This will hinder severe hail potential. However, there will be a
strong wind maximum passing over the area, leading to effective
bulk shear up to 50 kts. There will be fairly strong 925-850mb
winds in south-central AZ, up around 40-50 kts, and any stronger
storm that develops could mix down these stronger winds to the
surface. There will also be a non-zero chance of a brief tornado
in south- central AZ with sfc-1km SRH up to 100-150 m2/s2. The
strong winds above the surface will likely lead to gusty winds
across south- central AZ regardless this afternoon, with gusts
even upwards of 30-40 mph in some areas, but there is some
uncertainty how much low-level mixing will really occur. Some of
the higher elevation spots east of Phoenix have better odds (~50%
chance) of experiencing occasional advisory-level winds (>39 mph
gusts).

By sunrise Monday, the threat of rain will come to an end and
winds will die down as the trough axis pushes east of the state
and much drier air is ushered in. PWATs are forecast to quickly
drop to around 0.4-0.6" by sunrise Monday. Patchy fog cannot be
ruled out Monday morning in sheltered valley locations, but dry
air entrainment into the surface layer may preclude any formation.
As mentioned already, runoff and elevated flow in many of the
major waterways across south-central AZ is likely to continue
through Monday. Temperatures the next couple of days will remain
cool, with highs around 6-10 degrees below normal, mostly in the
upper-60s to middle-70s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Through the middle of the upcoming work week, following the
departure of this dynamic weekend system, we can expect dry
conditions, and transient upper level ridging, resulting in
temperatures slowly warming closer to seasonal levels (despite
daytime highs likely remaining a few degrees below the daily
normals). By late week, ensembles diverge with respect to another
disturbance possibly moving through the area, but guidance seem
to be trending toward a relatively weak transient upper
low/positively tilted shortwave that is then followed by more
ridging by the end of next weekend. Regardless of the outcome,
fairly benign conditions seem to be the most likely outcome. The
trajectory of the late week system is not favorable for rain
chances, with its residence time too short for better quality
moisture to be pulled into the area, and if it remains an open
wave, its positive tilt does not bode well for providing upper
level support for precipitation. NBM PoPs with the latest forecast
have fallen to 10% or less Friday into Saturday.

&&

.AVIATION...Updated at 1130Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT;

Considerable aviation weather impacts are expected to continue
through the daytime hours, with long duration SHRA and periods of
IFR-MVFR CIGs and VIS. A few terminals may near alternate
minimums due to the low CIG & VIS, particularly as a band of
heavier showers moves through on the leading edge of the
approaching weather system between 16-21Z. Confidence in sub-VFR
conditions remains high and has been observed sporadically through
the overnight hours. A break in the RA is expected this afternoon
but VCTS/VCSH will hang on into the evening. The best time to see
TSRA at the terminals will be between 22-04Z. Winds will favor SE
for the next few hours, then S by mid morning as speeds gradually
increase. Gusts to 15-25 kts are expected to develop by mid-late
morning, then peak as high as 30-35 kts this afternoon as
directions gradually veer from S to SW. This will present at least
a temporary southerly crosswind concern for KPHX. CIGs should
quickly clear this evening (and potentially sometime during the
afternoon depending on the coverage of TS that develop), and winds
will settle out of the W, eventually relaxing AOB 10 kts.

Southeast California/Southwest Arizona including KIPL and KBLH:

The primary aviation concern will be a period of sub-VFR CIGs
and/or VIS as SHRA impacts the terminals for the next several
hours, followed by SW-W winds gusting up to around 25 kts this
afternoon into the early evening. While CIGs and VIS will
generally favor an MVFR category this morning, a period of heavier
rain could push them briefly into an IFR category, more likely at
KBLH. CIGs will quickly clear late this morning, and SKC skies
should prevail by tonight.

&&

.FIRE WEATHER...
Widespread wetting rainfall is expected across the area today with
the highest rainfall totals expected in the high terrain north
and east of Phoenix. Rainfall will become more isolated this
afternoon and evening, with potential for isolated thunderstorms
as well. Gusty SW winds are also expected this afternoon and
evening, with peak gusts up to 30-40 mph possible in the lower
deserts of south-central AZ to 40-50 mph at the highest elevations
east of Phoenix. Any thunderstorm may also produce locally strong
to severe wind gusts. Minimum humidities will range between
55-80% areawide today and overnight maximum humidities up to
80-100%. Notably drier conditions are expected Monday through the
rest of the week, but minimum humidities will still remain around
30-45% each day as temperatures will be near to slightly below
normal. Winds for much of the rest of this week will return to a
more typical diurnal pattern with light speeds and modest
afternoon upslope gustiness.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch through late tonight for AZZ534-537>563.

CA...None.
&&

$$

SHORT TERM...Benedict
LONG TERM...Benedict/Whittock
AVIATION...Whittock
FIRE WEATHER...Benedict