699
FXUS65 KPSR 102059
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
159 PM MST Thu Sep 10 2026

.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/...
The high remains centered over southwestern AZ and southeastern
CA with generally easterly flow aloft over the region. Mid to high
level moisture has stayed put with 1000-700 mb mixing ratios
still ranging between 10-12g/kg across the lower deserts and into
the eastern high terrain. While we have plenty of moisture (PWATs
140-160% of normal), with a strong lower level subsidence
inversion in place convection will struggle to have any
development for most areas, especially after SE AZ had extensive
activity last night, which may have overworked the atmosphere too
much for anything developing tonight. This is reflected in the
latest CAMs and HREF showing <10% chance of activity in the far
eastern high terrain, but near a 30% chance of light showers
later this afternoon in western Imperial County, with convection
already visible on satellite developing in Northern Baja.

The peak strength of the ridge occurred late yesterday, translating
to peak temperatures today with the highs between 106F-110F in SC AZ
and 108F-112F in the western lower deserts and along the Colorado
River Valley. Additionally, the lower deserts of southeast
California are expected to feel especially unbearable as heat indices
will be up to around 115 degrees today. With above normal
temperatures and more humid conditions be sure to take extra care
when spending time outdoors. The Extreme Heat Warning remains in
effect through this evening for SC AZ, and the Phoenix Metro, and
through Friday evening along the Colorado River Valley, Yuma area,
and southeastern Imperial Valley. 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.

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 latest NBM run continued to show
PoPs between 25-25% over SC AZ and eastwards, however with the
atmospheric conditions expected to be in place PoPs have been
reduced to 5-15% with the higher range being mostly confined to
the east of Phoenix. 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, mostly in the western
portion of the CWA. 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...Ryan/Kuhlman
LONG TERM...Kuhlman
AVIATION...RW
FIRE WEATHER...Ryan/Kuhlman