340
FXUS65 KPSR 101735
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1035 AM MST Thu Sep 10 2026

.UPDATE...18Z Aviation Discussion

&&

.KEY MESSAGES...

- Above normal temperatures will prevail through the rest of the
  week, with Extreme Heat Warnings in effect for portions of the
  lower deserts.

- Daily chances for scattered showers and isolated thunderstorms
  will continue to be focused over the Eastern Arizona high
  terrain. Any chances for lower deserts should be confined to
  late Friday and again Sunday into Monday.

- Cooling temperatures over the weekend into early next week
  should eventually push readings back into the normal range by
  around next Tuesday.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
Strong high pressure is currently planted over the Southwestern
U.S., but moisture levels have improved enough to bring some
isolated showers and a few embedded storms over the past several
hours. The high center is currently situated over far west-central
Arizona resulting in northeasterly mid-level flow, but west
southwest lower level flow over much of Arizona. Moisture has
increased enough in the lower levels to push mixing ratios to
around 10 g/kg over much of the area to upwards of 12 g/kg over
southeast Arizona, but a strong lower level subsidence inversion
is also in place. Convection was quite extensive during the
evening hours across southeast Arizona/southwest New Mexico with
this complex sending a low level outflow and mid-level gravity
wave east northeastward through the rest of Arizona. Isolated
showers have popped off with the passage of these features,
tapping into elevated instability. We do not anticipate anything
more than very light rainfall amounts with any of these showers
with a focus mostly across western Maricopa into La Paz Counties.

For the rest of today, guidance is showing much more limited
convection than yesterday, in particular across southeast Arizona.
The subsidence inversion is likely to too strong, keeping chances
below 10% across our CWA. Guidance does show some convection
developing south of the U.S./Mexico border during the evening, but
it seems quite unlikely it will send anything up our way like what
is currently happening. The peak strength of the ridge occurred
late yesterday and this will translate to the hottest
temperatures occurring today. The lower deserts of southeast
California are expected to top 110 degrees with heat indices up
to around 115 degrees, while the Arizona lower deserts should see
highs of 107-110 degrees and heat indices closer to 110 degrees
during the afternoon hours.

The upper level ridge will continue to weaken today into Friday,
likely weakening enough to lower temperatures a good 2-4 degrees
across south-central Arizona starting Friday and 1-3 degrees over
the western deserts. The Extreme Heat Warnings will continue
through Friday for much of the lower deserts of southeast
California and southwest Arizona, while expiring everywhere else
this evening.

Friday should also bring another influx of moisture from the south
southwest, pushing area low level mixing ratios more into a 11-12
g/kg range. However, this may still not be enough to spark off
more widespread convection as the the subsidence inversion will
still be in place (albeit slightly weaker) and the steering flow
is expected to turn out of the southwest. We are expecting better
storm coverage across the eastern Arizona high terrain on Friday,
but with a southwesterly steering flow it will be hard to get
convection to fire over the lower deserts. The NBM does indicate
25-35% PoPs Friday evening/early Friday night from Phoenix
eastward, but that seems too optimistic. If storms do actually get
going over the south-central Arizona lower deserts Friday
evening, they will be within a high DCAPE environment which means
strong winds will be a possibility.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Forecast confidence for the weekend into next week remains quite
low, especially when looking at moisture levels and rain chances.
Guidance does agree the subtropical ridge will get pushed to the
east of our region over the weekend as a Pacific trough moves
through the northern tier states, but the GEFS is stronger and
farther south with the trough compared to the EPS. The models also
differ in the amount of moisture and rain chances during the
period with the GEFS favoring better rain chances from Phoenix and
areas east of Phoenix over the weekend, while the EPS favors
better chances by Tuesday into the middle of next week. Needless
to say, these differences do not inspire much confidence in the
available NBM/WPC PoPs.

The latest forecast places little if any PoPs on Saturday and
Saturday night, which seems fairly reasonable, but then seems to
be under doing chances late Sunday. The increased PoPs of 20-40%
then seem too high for Monday before gradually lowering during the
middle part of next week. Lately, guidance has had a tendency to
place fairly high PoPs during the 4-8 day range, just to back off
as it gets into the short-term. It would seem everything would
have to come together nearly perfectly with the trough passing by
to our north close enough, but not too close to scour out what
moisture we have in the low/mid levels. Additionally, if the
subtropical ridge becomes more dominant, then we will have to
worry about too strong of a subsidence inversion. Given the fairly
high model uncertainty, the forecast is likely to change.

The temperature forecast is also of lower confidence with a fairly
wide spread starting Monday. At the moment, NBM forecast
temperatures call for readings more in the normal range by early
next week, but given the higher model spread we could end up
with readings slightly below or even slightly above normal.
Guidance at least mostly agrees on the `coolest` temperatures
falling on next Tuesday and Wednesday before trending upward
again during the latter half of next week.

&&

.AVIATION...Updated at 1735Z.

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

No major aviation concerns are expected during the TAF period.
Winds will follow familiar diurnal trends with perhaps some
afternoon gusts in the mid-teens to around 20 kt. After relaxing
slightly, westerly flow will likely rebound overnight, delaying
the the typical east shift toward the mid-morning timeframe. FEW
to sometime SCT mid- and upper-level cloud decks will be present
over the region through Friday morning.

Southeast California/Southwest Arizona including KIPL and KBLH:

The main aviation concern will be the potential for gusty outflow
winds from distant convection at KIPL this afternoon. A TEMPO
group has been added to the TAF to reflect such a boundary, but
strength remains uncertain. There has been a consistent signal
that time of occurrence will happen sometime between 22-01Z this
evening. Outside of this, winds are expected to follow diurnal
trends at each terminal under a FEW to sometimes SCT mid- and
upper-level cloud decks.

&&

.FIRE WEATHER...
Above normal temperatures will continue into the weekend with
modestly elevated humidities. Rain chances will improve by
Friday, but still mostly favor the Arizona high terrain.
Afternoon minimum humidities of 17-25% today will improve to
25-30% for Friday and Saturday. Overnight recoveries will remain
fair to good at 40-70%. Expect fairly typical diurnal winds with
little if any breeziness today, but with 20-25 mph afternoon and
early evening gusts on Friday and Saturday. Chances for isolated
showers and thunderstorms are likely to remain possible across
the eastern districts through at least early next week while
temperatures eventually fall back into a normal range.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ530-532-533.

     Extreme Heat Warning until 8 PM MST this evening for AZZ531-
     535>544-546-548>551-559.

CA...Extreme Heat Warning until 8 PM PDT Friday for CAZ562-566-567-
     569-570.

&&

$$

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