261
FXUS65 KPSR 212054
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
154 PM MST Tue Jul 21 2026

.KEY MESSAGES...

- Shower and thunderstorm chances will continue today, especially
  over the Arizona high terrain. Isolated storms and gusty storm
  outflow winds can also be expected into the south-central
  Arizona lower deserts.

- Drying conditions starting Wednesday will mostly end monsoon
  storm chances by Thursday.

- Extreme Heat Warnings are in effect for all of the lower
  deserts for the latter half of the week as hot and humid
  conditions will develop over the next couple of days.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
The inverted trough can be seen on GOES mid-lvl WV imagery along
the AZ/NM border. This feature will progress through northeastern
AZ this afternoon/evening bringing positive vorticity`s embedded
within, aiding in storm ascent. This system will help promote
another round of thunderstorm activity in the eastern higher
terrain, very similar to yesterday`s activity. Current mesoscale
analysis shows divergence aloft in western NM within the cyclonic
flow of the inverted trough, with additional divergence aloft in
southern NM. Additionally, PWATs across the region remain between
1.5-1.7" in the eastern portions of the CWA with PWATs upwards of
2" in the western lower deserts. While the western lower deserts
have higher PWATs than the eastern higher terrain, forecasted
MUCAPEs out west are between 100-500 J/kg, while the eastern
portions will range between 750-1500 J/kg, due to this, a
majority of activity will be confined in the eastern portions of
the CWA. Between the moisture, CAPE, divergence aloft, positive
vorticity, and the natural lift of the terrain, much of the
Arizona high terrain has been placed under a Flood Watch, with
localized rainfall amounts of greater than 2" possible.

Again, similar to last night, gusty winds and patchy blowing dust
will be the main concerns over the Phoenix metro and lower
deserts with HREF members showing a 50-70% chance of wind speeds
above 35 mph this evening, and the HRRR again optimistic of an
outflow from the higher terrain moving through with speeds near
35-40 mph. A few storms may be able to survive for a short period
of time before diminishing, with max PoPs between 30-40% late
tonight, but most areas are not likely to receive more than 0.25"
and many areas may not receive anymore than a few hundredths of an
inch.

By Wednesday winds aloft are expected to shift out of the south to
southwest which will aid in the advection of drier air into the
region. Due to this shower and storm chances drop considerably with
PoPs in the higher terrain between 15-30% and less that 10% across
the lower deserts. With that abrupt shift, the region will also
begin to warm, with H5 heights forecasted to climb between
591-594 dam across the Desert SW starting Wednesday, pushing high
temperatures in south central AZ into the low to mid 100s and then
into the mid to upper 100s to locally higher across SE CA and SW
AZ. This has lead to the Extreme Heat Watch to be upgraded to an
Extreme Heat Warning for SE CA starting Wednesday. Please ensure
to take proper heat safety precautions.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Extreme Heat is expected to impact much of the area late this
week through at least the weekend as the subtropical ridge
strengthens while the center gradually shifts over the region
Friday into Saturday. Record or near record climatological H5
heights are forecast across New Mexico starting Thursday,
eventually moving into Arizona Friday into Saturday with H5
heights potentially reaching 598-600dm over Arizona. Major
HeatRisk is expected to impact all of the lower deserts starting
Thursday, becoming even more widespread Friday into the weekend as
localized areas of Extreme HeatRisk may develop. The forecast
highs of 110-116 degrees Thursday through next Monday (below
records) is masking the potential severity of this heat wave as
dew points and humidities are expected to remain elevated. Heat
indices are likely to reach 113-120 degrees over the lower deserts
starting Friday with the highest readings across southwest
Arizona and southeast California. Overnight lows will also become
very warm with readings not likely falling much below the upper
80s. Lower 90s can be expected for much of the urban core of
Phoenix starting Thursday night. If we do end up mixing out more
of the boundary layer moisture, the higher end of NBM guidance
shows highs potentially reaching 116-118 degrees in the Phoenix
area to as high as 117-120 degrees for portions of southeast
California.

The hottest days are likely to be Friday-Sunday, but there is more
forecast uncertainty by Sunday as some guidance indicates some
moisture return this weekend and the potential for more
convective activity. For now, we are not expecting much if any
high terrain showers or thunderstorms Thursday and Friday, but
that could change starting Saturday or Sunday. Any more extensive
convective activity may eventually disrupt the extreme heat, at
least over eastern and possibly into central Arizona by Sunday or
Monday. If we don`t get relief from storm activity, guidance at
least heavily favors some weakening of the ridge early next week
while also shifting it farther to the east.

&&

.AVIATION...Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty outflow winds and modest chances for SHRA/TSRA this evening
are the primary weather issues under periods of mid/high cloud
decks. TSRA forming over higher terrain to the north and east
should send gusty outflows and an abrupt wind shift towards the
Phoenix terminals. Chances for outflow gusts exceeding 30 kts will
be around 30-50% across the Phoenix terminals. New shower and
thunderstorm development may occur along the outflow boundaries
with chances of SHRA around 30-40%. Any thunderstorms that develop
will create gusty, erratic winds. Outside of this, winds will
continue to veer toward the W heading into this afternoon with a
few gusts into the teens.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Wednesday morning under
a few passing mid/high cloud decks. Winds will generally favor a
south direction at KBLH, while directions will predominantly favor
the west at KIPL. Periods of variability will be possible at KIPL
through the afternoon before gusty sundowner winds are expected to
pick up this evening, with gusts to around 20-25 kts at times.

&&

.FIRE WEATHER...
Much of the shower and thunderstorm activity will be over the
Arizona high terrain today while gusty storm outflow winds will
be the main concern today for the south-central Arizona lower
deserts. Chances for showers and storms will quickly drop off
Wednesday with little if any activity expected Thursday as hotter
and drier conditions settle into the region. Humidities will
remain elevated today with MinRHs of 30-50% across the eastern
districts, while the western districts will dip to 15-25%. MinRHs
will then dip to 15-20% across all of the lower deserts starting
Thursday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Monday for
     AZZ530-532.

     Flood Watch until 10 PM MST this evening for AZZ556-560-562-563.

     Extreme Heat Warning from 10 AM Thursday to 8 PM MST Monday for
     AZZ531-533>555-559.

CA...Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Monday for
     CAZ562>570.

     Extreme Heat Warning from 10 AM Thursday to 8 PM PDT Monday for
     CAZ560-561.

&&

$$

SHORT TERM...Ryan
LONG TERM...Kuhlman
AVIATION...Smith/18
FIRE WEATHER...Ryan/Kuhlman

NWS Phoenix Office