420
FXUS65 KPSR 192040
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
140 PM MST Mon Oct 19 2026

.KEY MESSAGES...

- A weak disturbance will spark scattered showers and isolated
  thunderstorms this afternoon, mainly across the Arizona higher
  terrain east of Phoenix.

- Temperatures Tuesday will warm near to slightly above normal
  before abrupt cooling takes place by the latter half of the
  week.

- A Pacific low pressure system moving into the region during the
  middle portion of the week will bring increasing rain chances,
  mainly across south-central and eastern Arizona, with the
  potential for multiple rounds of moderate to heavy rainfall as
  well as some strong thunderstorms.

&&

.SHORT TERM /Today through Tuesday/...
Early afternoon satellite WV imagery shows a weak shortwave
trough progressing across Arizona, aiding in shower and isolated
thunderstorm development across the higher terrain. Sufficient
moisture and instability combined with orographic and dynamic
ascent will allow for continued shower and thunderstorm
development this afternoon. The greatest focus of this activity
will reside across southeastern portions of the state where
moisture and instability parameters are best. However, HREF
guidance supports some of this convective activity making its way
into southern Gila County this afternoon with gusty outflow winds
and locally heavy rainfall being the primary concerns. Across the
south-central Arizona lower deserts, conditions won`t be as
favorable, but a few isolated showers and storms may develop,
particularly around the Table Top area. Quieter weather is
expected Tuesday as the weak shortwave exits to the northeast and
the greatest rain chances stay confined to the White Mountains
Tuesday afternoon.

Heights rebound across the region Tuesday in the wake of the
exiting shortwave and ahead of a potent approaching weather system
digging southward along the West Coast. Forecast highs warm
several degrees Tuesday afternoon compared to today as
temperatures climb into the upper 80s to lower 90s.

&&

.LONG TERM /Wednesday through Sunday/...
A much more active weather pattern is shaping up to take place by
the middle portion of the week as a deep upper-level low
amplifies off the CA coast and then moves inland over the Desert
Southwest through the remainder of the work week. Latest ensemble
and deterministic model suite have come into a better agreement in
showing a deep upper-level low with strong negative height
anomalies becoming established off the southern CA coast on
Wednesday and potentially obtaining a slight negative tilt. This
will cause the flow aloft to become established more out of the
south, advecting deeper moisture northward into the region
starting Tuesday night. In fact, both the EPS and GEFS show PWAT
values peaking above 250% of normal with the North American
Ensemble Forecasting System depicting moisture levels approaching
near record values for mid-October. In addition, the combination
of the deeper moisture as well as steeper mid-level lapse rates
will likely lead to significant instability with both the ECMWF
and GFS indicating MUCAPE values approaching 1000 J/KG. Therefore,
the combination of the strong synoptic ascent from the trough and
favorable thermodynamic parameters will likely lead to multiple
rounds of showers and thunderstorms to break out across much of
south-central AZ Wednesday through Thursday afternoon, period when
rainfall chances will be highest, while much of the western
deserts should remain mostly dry given that the greatest moisture
advection will occur mostly over central and eastern AZ.

With the moderate levels of instability likely to be in place, any
shower and thunderstorm activity will be capable of producing
rainfall rates in excess of 1-2"/hr with training of activity likely
to be an issue. Thus, there will be a heightened potential for flash
flooding, especially across the foothills and higher terrain areas
to the north and east of Phoenix where upslope flow will likely
enhance the activity. Given this heightened potential for flash
flooding, the Weather Prediction Center has placed areas from
Phoenix and points north and east in a slight risk for excessive
rainfall leading to flash flooding for both Wednesday and Thursday.
In terms of rainfall amounts, the latest forecast from the Weather
Prediction Center has much of the foothills and higher terrain areas
north and east of Phoenix potentially receiving upwards of 1.00-
2.50" while across the lower deserts, including the Phoenix metro,
amounts are likely to be lower ranging between 0.25-1.00", although
locally higher amounts will be likely in areas that see training of
activity. In addition to the heavy rainfall threat, given that the
0-6 km shear will be in excess of 50 kts combined with the
moderate levels of instability, there will also be the threat of a
few strong to severe storms capable of producing strong wind
gusts and hail.

As the upper-level low moves inland into the southern Great Basin
late Thursday, strong dry air advection will gradually push eastward
ending rain chances by Thursday afternoon across the south-central
AZ lower deserts with rain chances lingering into early Friday over
the higher terrain. There are indications from guidance of a
follow-on shortwave moving through area late Friday through
Saturday, however, it should be inconsequential given that there
will be an abundance of dry air in place limiting any potential
for additional rainfall.

Under the influence of the general troughing pattern as well as the
heightened rain chances, temperatures by the latter half of the week
will rapidly cool off towards readings that will be several degrees
below normal. The latest NBM shows much of the lower deserts
struggling to reach 80 degrees for afternoon highs both Thursday and
Friday, with Friday likely to be coolest day. Temperatures will
gradually warm up next weekend but still remain below normal.

&&

.AVIATION...Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation concerns are expected through the TAF period.
Winds will remain light, generally aob 5 kts, with a predominant
S-SE component through the afternoon before a gradual transition
to westerly by late this afternoon/early this evening. Winds will
shift back out of the east around midnight. There is a low chance
(10%) for a passing shower, mainly at KPHX and KIWA this afternoon,
however no impacts are expected at the terminals. FEW to SCT mid-
level clouds will persist over the terminals, with the lowest
bases around 7-8 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected over the next 24 hours under
mostly clear skies. KIPL will maintain a light easterly component
before switching out of the west late tonight. KBLH will see a
brief southerly component, however extended periods of calm and
vrb can be expected. Overall speeds will remain aob 5 kts.

&&

.FIRE WEATHER...
Wind speeds through Tuesday will generally be light with limited
afternoon gustiness before increasing towards the middle of the
week ahead of an approaching weather system. Scattered showers and
isolated thunderstorms are expected across the higher terrain
areas of the eastern districts this afternoon. Rainfall chances
temporarily decrease on Tuesday before increasing substantially
across much of south-central and eastern AZ by the middle of the
week with rainfall amounts likely to be greater than 0.50-1.00",
especially east of Phoenix. Minimum humidity levels in a 30-50%
range will be common throughout the week with even higher readings
likely across eastern districts with good to excellent overnight
recoveries. Temperatures will be in a near normal range during the
next couple of days before falling into a below normal category
by the latter half of the week.

&&

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

$$

SHORT TERM...Smith
LONG TERM...Lojero
AVIATION...Salerno
FIRE WEATHER...Lojero

NWS Phoenix (PSR) Office