367
FXUS65 KPSR 152301
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
400 PM MST Sat Aug 15 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES....

- Dry conditions, partly cloudy skies, and near normal temperatures
are expected this weekend.

- Extreme Heat Warning will be in effect for the lower deserts of
southeast California and southern and central Arizona for much of
next week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...

Southwest flow during the monsoon is not ideal for rain chances,
especially across the lower deserts, unless there was a tropical
system, which there is not, or a trough moving through, which there
also is not. So, pretty quiet monsoon conditions are expected this
weekend through the beginning of next week as the southwest flow
aloft persists, with near to slightly below normal moisture levels.
Dew point temperatures will actually be on the decline through
Monday, with guidance showing most lower deserts falling to 50-55
degrees in the afternoons and possibly even dipping below 50 degrees
in some locations. A few weak showers or storms may still develop
over terrain favored areas today, but instability is very low
(couple hundred J/kg CAPE at most). So, updrafts will struggle and
be short lived. With lowering dew points instability will be even
less the next few days. Latest HREF neighborhood probability and
paintballs for >40dBZ radar echoes shows almost no coverage for
Sunday afternoon, except for far southeast AZ. There will be weak to
moderate ascent for some light showers late tonight through Sunday
morning across SoCal and western AZ, from a passing shortwave
trough, but likely not enough rain will reach the ground to measure
(>0.01").

Strong high pressure is still seen on satellite displaced well to
the east, over the southern Mississippi River states, and large
scale troffing is positioned to the west. Height fields over the
local area have steadily risen over the past couple of days and
latest objective analysis shows H5 heights around 592-594dam, which
is close to the 90th percentile of climatology. Temperatures at
850mb have also warmed a few degrees. This will lead to surface
temperatures this afternoon peaking near normal, in the 102-106
degree range for the lower deserts. Around 2-3 degrees of warming is
expected into Sunday and another 2-3 into Monday, which will bring a
return of highs reaching or exceeding 110 degrees in the lower
deserts and Major HeatRisk beginning Monday. The Extreme Heat Watch
has been upgraded to a Warning starting Monday for all areas
previously under the Watch. The coverage of Major HeatRisk becomes
more widespread by Tuesday as temperatures continue to warm, with
highs forecast to reach 5-7 degrees above normal and low
temperatures warming back into the upper 80s to around 90 degrees in
the lower deserts.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/....
The weather pattern for most of next week will see the subtropical
high becoming the dominate feature across the Southwestern U.S.
while its strength will barely change. Guidance agrees the ridge
center will shift from Texas on Monday to somewhere over Arizona by
Wednesday with H5 heights rising to 595-597dm. H5 heights of this
magnitude will represent the 97th percentile of climatology for the
period and temperatures will follow with forecast highs only falling
short of daily records by a few degrees each day. Since moisture
levels are now expected to remain fairly limited for much of, if not
all of, next week, the day-to-day convective potential should remain
quite low and likely confined to far eastern Arizona. The most
likely scenario keeps the ridge in full control over the Desert
Southwest with the center hovering somewhere over Arizona and/or
into western New Mexico.

There is moderate to high confidence for a more prolonged heat event
leading to the now Extreme Heat Warning covering all lower deserts
and extending through Friday. NBM forecast highs show readings
anywhere from 108-113 degrees across the lower deserts each day next
week with overnight lows near the 90 degree mark by Tuesday-
Wednesday as surface dew points shift a bit higher. Forecast Major
HeatRisk has also expanded more across the western lower deserts
going into the middle part of next week with the bulk of the area
keeping Major HeatRisk levels through at least next Friday. There is
uncertainty in the length of time this heat event will last as some
of the guidance shows the ridge center may eventually shift more to
the north and/or east. If this occurs, it should help to increase
the amount of monsoon activity over the region, eventually leading
to some degree of cooling.

&&

.AVIATION...Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No weather concerns will exist through Sunday evening under periods
of mid/high cloud decks. Wind behavior will be nearly identical to
the past 24 hours featuring a later than usual overnight easterly
wind shift, and extended periods of variable directions.


Southeast California/Southwest Arizona including KIPL and KBLH:
No weather issues will exist through Sunday evening under
occasionally thick mid/high cloud decks. Trends in winds will be
similar to the past 24 hour including modest afternoon/evening
gusts, and periods of nearly calm conditions in the morning.

&&

.FIRE WEATHER...
Dry conditions and near normal temperatures will prevail this
weekend before temperatures rise to above normal next week. Little
if any monsoon storm activity is expected over the next several days
with only isolated afternoon storms possible over the far eastern
districts. Humidity levels will continue to drop through Monday with
afternoon MinRHs falling into the teens across the lower deserts to
around 25% for higher terrain areas starting Sunday. Expect overall
light winds generally following typical diurnal patterns.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM Monday to 8 PM MST Friday for
     AZZ530>544-546-548>551-553>555-559.

CA...Extreme Heat Warning from 10 AM Monday to 8 PM PDT Friday for
     CAZ562-565>567-569-570.

&&

$$

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