027
FXUS65 KPSR 052316
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
415 PM MST Mon Oct 5 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- Above normal temperatures with minimal day to day changes will
exist through the majority of the week as afternoon highs reach 97
to 103 degrees across the lower deserts.

- An Extreme Heat Watch is in effect for portions of southeast
California and southwest Arizona on Wednesday and Thursday as
temperatures warm to near record levels and lead to major HeatRisk.

- Dry weather with zero rain chances will persist through Saturday
with shower and storm chances returning to Arizona as early as
Sunday.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
It has been another breezy day across southern AZ, but winds have
not quite as strong as yesterday due to a weakening pressure
gradient. Surface pressure to the east is lowering which is allowing
the east-west gradient to relax. This weakening will continue
through tomorrow morning. So, there will still be some breeziness in
the morning tomorrow before the gradient fully relaxes and winds
return to a more typical light diurnal pattern.

High pressure remains in place over the Southwest, with midday
objective analysis showing H5 heights around 591dam, which is just
above the 90th percentile based on sounding climatology. This high
pressure, and mostly clear skies, will continue to support above
normal temperatures across the region. Latest aircraft soundings out
of Phoenix show little change in the low-level thermal profile over
the last 24 hours. So, high temperatures this afternoon will be
nearly identical to yesterday, with lower deserts topping out around
97-103 degrees.

Heading through tomorrow and Wednesday a weak shortwave currently
over northern NV is expected to turn southeast and drop through
northeast AZ on Wednesday while a strong anticyclone develops near
the coast of SoCal. While the shortwave may lead to isolated showers
and storms up along the Mogollon Rim Wednesday, the lower deserts
are expected to remain dry. The shortwave will also help keep south-
central AZ from seeing a significant warm-up, unlike areas to the
west. Temperatures tomorrow will still be similar to today, if not a
degree warmer, and then temperatures warm 2-4 degrees into
Wednesday, with nearly all lower desert locations reaching 100
degrees in the afternoon. Temperatures will be hottest across
southeast CA and along the Lower Colorado River Valley, including
Yuma, where highs on Wednesday will reach the 104-107 degree range,
which is upwards of 11-14 degrees above normal for early October and
will be near daily records. An Extreme Heat Watch remains in effect
starting Wednesday for the Imperial Valley, CA and Yuma, AZ.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
A strong anticyclone is expected to persist near the SoCal coast
through at least Thursday, which will keep temperatures well above
normal and near daily records across SoCal. Temperatures are also
expected to warm another 1-2 degrees across south-central AZ on
Thursday, following the passage of a weak shortwave trough. Even
south-central AZ will see high temperatures up to 10 degrees above
normal (99-102 degrees) on Thursday. An Extreme Heat Watch remains
in effect through Thursday for Imperial Valley, CA and Yuma, AZ,
where probabilities of Major HeatRisk are highest (50-70%). This
watch is likely to be upgraded to a warning tonight or tomorrow
morning and Friday is being considered for the heat alert as well.
Latest NBM forecast shows 30-50% Major HeatRisk probs on Friday for
the same areas under the current watch.

The coastal anticyclone is expected to breakdown heading into Friday
as the synoptic pattern shifts, with a Pacific low moving toward the
CA coast, but low level temperatures are expected to remain very
warm. Latest global ensembles show 850mb temps cooling by only a
degree or two centigrade into Friday, which should only result in 1-
4 degrees of surface cooling from Thursday. Latest high temperature
forecast for Friday has 101-106 degrees across southeast CA and
southwest AZ to 97-101 degrees across south-central AZ.

As alluded to, the pattern will shift heading into the end of this
week and this weekend with a trend toward troffing and negative
height anomalies across the Western CONUS. While there is good
confidence in the trough pattern developing, there is still a lot of
model uncertainty/spread regarding how the trough pattern will
evolve heading into the end of the weekend and start of next week.
It does look like the Pacific low that will near the CA coast on
Friday will dip south this weekend and interact or faze with TC
Rachel while at the same time a trough will move out of the Gulf of
Alaska and strengthen as it moves south down the northern Pacific
coast. There are certainly a lot of eyes on what will happen with TC
Rachel and whether or not it will help bring rain to the Desert
Southwest, just like with TCs Odalys and Polo early last week.

Latest guidance has trended toward an eventual turn to the northeast
by Rachel by the end of the weekend. While this trend does lend
itself in favor of a push of moisture toward the Southwest CONUS,
there is still a lot of uncertainty in the forecast this far out,
especially with timing and evolution of the trough moving down the
northern Pacific coast and how that may affect the remnants of
Rachel. Current thinking is at least mid and high level moisture
will eventually shear off or Rachel up toward the Southwest, which
may bring showery activity as early as Sunday and then the more
potent coastal trough/low will help drive additional shower and
storm chances across AZ, while also sending a cold front and cooler
temperatures through the region early next week. Again uncertainty
is still high and it is ill-advised to buy into single deterministic
long-range model runs that may show a strong tropical circulation
pushing into the U.S.

&&

.AVIATION...Updated at 2315Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No weather issues will exist through Tuesday evening under a few
midlevel cloud decks. Confidence is excellent that easterly winds
will persist well into Tuesday afternoon with far less gustiness
than the past few days. Confidence is increasing that wind
directions will finally complete the traditional westerly switch
late Tuesday afternoon/evening.


Southeast California/Southwest Arizona including KIPL and KBLH:
No weather issues will exist through Tuesday evening under clear
skies. Winds will continue to oscillate between NE and NW with
speeds under 10kt and extended periods of nearly calm conditions.

&&

.FIRE WEATHER...
Dry conditions with well above normal temperatures will continue
through the week, with afternoon high temperatures reaching up to
100-107 degrees across the lower deserts (hottest on Thursday).
Breezy easterly winds will continue across southern AZ through this
afternoon and Tuesday morning, with gusts up to 20-25 mph. Winds
will return to their more typical light diurnal tendencies  Tuesday
afternoon through Thursday, with only minor afternoon upslope
gustiness. A gusty easterly gradient wind is expected to develop
again by Friday and last through Saturday. MinRHs will mostly range
from 15-25% across the western districts to 20-35% across eastern
districts through the week with fair to good overnight recovery (35-
60%) area-wide. Humidities will be lowest on Thursday when
temperatures are likely at their hottest, but winds will still be
light at this time, so there are no elevated fire weather concerns.
No wetting rain expected through at least Saturday. Rain chances
then go up by the end of the weekend/start of next week with
increased moisture and a potential weather system moving through.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Watch from Wednesday morning through Thursday
     evening for AZZ532.

CA...Extreme Heat Watch from Wednesday morning through Thursday
     evening for CAZ566-567.

&&

$$

SHORT TERM...Benedict
LONG TERM...Benedict
AVIATION...18
FIRE WEATHER...Benedict