Weather alerts for the NWS Phoenix AZ forecast area

000
FXUS65 KPSR 281055
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
355 AM MST Wed Oct 28 2026

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Tranquil weather conditions will continue today and Thursday 
  with temperatures within a few degrees of daily normals.

- An unsettled weather pattern will return to the region from
  Friday through Sunday resulting in much cooler temperatures and
  enhanced chances for widespread rainfall.

- Embedded thunderstorms and heavier rainfall may affect some
  areas resulting in localized minor flooding, specifically 
  Friday and Sunday. 

&&

.SHORT TERM /Today through Thursday/... 
The current quiet weather conditions will abruptly come to an end
by Friday morning as the first of two weather systems affects the
region. Until then, other than some increasing higher level
clouds, not much will change. Our current westerly dry flow will
slowly shift more out of the southwest later today as a large
Pacific trough takes shape off the West Coast. The split flow
pattern supporting a strong upper low along the British Columbia
coast and a second much weaker disturbance well west of California
will stay distinct over the next couple of days, but that will 
change by the weekend. In the near term, the air mass currently in
place will hold fast, but with some upper level moisture shifting
in from the northwest bringing some fairly thin high clouds 
today. A second batch of high level moisture and clouds will move 
in directly from the west on Thursday, while increasing southerly 
flow in the low levels will also begin to advect subtropical low 
level moisture northward into south-central Arizona. Despite the 
increased cloudiness today and Thursday, daytime highs should hold
right near averages for late October.

&&

.LONG TERM /Friday through Tuesday/... 
Forecast confidence is increasing for two separate weather 
events, Friday through Sunday, both of which could bring impactful
rain amounts to portions of central Arizona. The increasing 
moisture on Thursday into Friday is expected to peak during the 
daytime hours Friday with PWATs reaching 225-250% of normals and 
low level mixing ratios of 8-9 g/kg, centered over Maricopa and 
Pinal Counties. Forecast soundings show the moisture will be quite
deep, extending fairly evenly throughout the column with modest 
elevated MUCAPE up to around 500 J/kg. Strong jet forced ascent is
also seen moving over the area on Friday combining with the 
modest southerly low level upslope ascent. 

Showers are expected to begin developing a few hours after 
midnight Thursday night before increasing in coverage and 
intensity by around sunrise Friday. Both the GEFS and EPS show QPF
maxima centered from Phoenix to around the Tonto NF with amounts 
averaging 0.50-0.75". Considering the available instability and 
steep mid-level lapse rates, we should expect scattered 
thunderstorms too, mostly embedded with the shower activity. 
General rainfall rates are likely to mostly fall within a 
0.05-0.2" range, but it would not be surprising to see very 
localized rates of around 1" per hour within any thunderstorms. 
These higher rainfall rates should pose a minor flood threat on 
Friday, mainly affecting area washes and the typical unbridged low
water crossings. There is potential for higher rainfall amounts 
with the NBM 75th percentile showing amounts between 1.5-2.0" 
centered over the foothills just north of Phoenix. A Slight Risk 
for excessive rainfall remains on the updated WPC ERO and based on
the model run-to-run consistency, Flood Watches are likely to be 
needed for at least north-central and northeast Maricopa County. 
The shower and thunderstorm activity should also extend eastward 
into Gila County later on Friday before quickly winding down 
Friday evening as we lose upper level support. 

The large scale trough will remain positioned along and into the 
Western U.S. into Saturday with the main low center near the
Pacific Northwest, but another strong shortwave diving into the 
base of the trough is expected to help bring another low 
developing off the coast of California Saturday night into Sunday.
Saturday is expected to be mostly a dry day, but there will still
likely be some isolated upslope type showers mostly focused over 
the high terrain north and east of Phoenix. However, this will 
just be the calm in between weather systems with the second one 
moving in starting late Saturday night expected to be stronger 
and more impactful.

By Saturday evening, guidance shows a strong atmospheric river
(AR) starting to make its way into northern Baja and far southern
California. By Sunday morning, the full force of this AR is
expected to be directed at southern Arizona and northern Sonora
Mexico with PWATs increasing to 275-325% of normal, or right near
record levels for our area this time of year. Compared to model 
runs 24 hours ago, the latest depicts even better moisture and a
stronger system. Upper level forced ascent should begin to
increase over our area by Saturday night, coinciding with
increasing low and mid level upslope south southwesterly flow.

A large area of light to moderate rain is likely to develop ahead
of the approaching weather system late Saturday night into early 
Sunday affecting the bulk of the region, particularly central and 
eastern Arizona. Although model uncertainty is decreasing, there 
is still a good deal of uncertainty in expected rainfall amounts. 
This looks to be a longer duration light to moderate rain event 
with limited instability keeping rainfall rates under 0.5" per 
hour and even lower across the lower deserts. However, because 
this may end up easily being a 6-12 hour rain event, the rainfall 
could quickly add up, especially into the higher terrain 
northeast of Phoenix where upslope forcing will be maximized. The 
latest NBM QPF shows a wide range of potential amounts with 
averages around 1" in the Phoenix area to upwards of 1.5-2" over 
the high terrain northeast of Phoenix. The lower end of the 
forecast shows amounts closer to 0.5" and 1-1.5" respectively, but
the higher end potential is more like 2-3". Considering this will
be the second rain event within 3 days, any additional moderate 
to heavy rain could compound any flooding issues that occur 
Friday. Rain chances may linger through Sunday night across 
portions of central and eastern Arizona, but by mid to late Monday
morning, much of the area should be drying out as the system is 
quickly pushes east of the area.

Temperatures during this unsettled weather pattern will fall below 
normal starting Friday with highs dropping to between 75F-80F before 
bottoming out closer to 70F highs for Sunday and/or Monday. It would 
not be out of the question for some lower desert communities stuck 
in prolonged rain Sunday to not even breach the 70F threshold. NBM 
guidance shows fairly large forecast temperature spread for the 
first half of next week as the large scale troughing may linger near 
the region with depressed H5 heights for a couple more days. If this 
happens, highs will very slowly creep upward through the low to mid 
70s, whereas if the ridge quickly takes over, highs closer to 80F 
would be more common by next Tuesday or Wednesday.

&&

.AVIATION...Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and 
Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns will exist through Thursday morning
under periods of thicker high cirrus. Winds will remain light,
generally AOB 8 kts, with a tendency towards SE'rly to S'rly 
directions during the daytime hours today. Confidence is low on a 
full westerly wind shift at the Phoenix area terminals, though a
light W/NW component could develop for a few hours around sunset.
Otherwise, expect extended periods of variability to nearly calm 
conditions.

&&

.FIRE WEATHER...
Dry conditions with near normal temperatures will persist through
Thursday under increasing cloud cover. Minimum humidity levels 
will fall into a 20-40% range following fair to good overnight 
recovery of 40-60%. Winds will remain unseasonably light with 
minimal upslope breeziness. Beginning Friday, several days of  
unsettled weather will affect the region with much higher 
humidities, widespread rainfall, and cooler temperatures.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman/18
AVIATION...Whittock
FIRE WEATHER...Kuhlman