371
FXUS65 KPSR 171737
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1037 AM MST Mon Aug 17 2026

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES....

- Temperatures will heat up several degrees above normal through
  at least the middle part of the week, with lower desert highs
  climb above 110 degrees most days.

- Extreme Heat Warnings are in effect today through Friday with
  widespread Major HeatRisk.

- Thunderstorm activity will be mostly confined to the Arizona
  high terrain over the next few days, but chances of affecting
  the lower deserts should increase by Wednesday or Thursday.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
Despite the subtropical ridge becoming the more dominant weather
feature across the Southwestern U.S., we are also contending with
a weakening easterly wave currently centered over far western
Texas. This disturbance will eventually lose out to the ridge as
it is forecast to shift southwestward over the next couple of
days, but it is at least expected to clip southeast Arizona later
today. As a result, some weak forcing across east-central and
southeast Arizona in combination with some modest moisture
advection should bring better coverage of showers and
thunderstorms this afternoon/early evening. Hi-res CAMs mostly
agree the bulk of this convection will move southeast of our CWA,
but a few storms may impact southern Gila County. As the
disturbance exits to the south southwest into Tuesday, convective
potential is likely to shift more to the Mogollon Rim but with
little expected impact for our area. Tuesday will also mark the
start of low level moisture advection into southeast California
and southwest Arizona from the south with even better and more
widespread moisture advection occurring on Wednesday.

Temperatures have noticeably warmed up over the past couple of
days with Phoenix, Yuma, and El Centro all reaching 110 degrees on
Sunday. The subtropical ridge moving into the region has pushed
H5 heights to between 594-596dm or well into the 90th percentile
of climatology. Ensemble mean H5 heights are shown to stay fairly
stable the rest of the week, but with the center of the ridge
reforming over the northern half of Arizona by Wednesday. Given
the little change in heights aloft and little if any influence on
temperatures from convection through at least Tuesday, we have
high confidence in forecast highs rising to 109-113 degrees across
the lower deserts. The Extreme Heat Warnings across the bulk of
the area go in effect later this morning with the coverage of
Major HeatRisk expanding into mid-week.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Forecast uncertainty has actually increased for the latter half
of the week as guidance is now favoring slightly better moisture
than previously shown while also repositioning the expected
subtropical ridge center closer to the Four Corners area by
Thursday. The forecast strength of the ridge has increased too,
but if the ridge center is more removed from southern and central
Arizona it will increase the convective potential. Although there
is a good amount of ensemble spread for Wednesday and Thursday,
the amount of members indicating QPF spreading into the lower
deserts has more than doubled. Forecast mean PWATs are now shown
to reach 1.3-1.5" Wednesday and 1.4-1.6" Thursday, or right around
normal for the latter half of August. If the ridge does in fact
end up moving far enough to the north, it should help to decrease
the CIN over the area by Thursday. As of now, Wednesday should
still involve mostly high terrain convection, but we can`t rule
out decent outflows pushing into the south-central Arizona lower
deserts. Despite the uncertainty, storm chances for Thursday have
definitely increased enough to go higher than NBM guidance. There
are also indications of shear increasing by Thursday which could
result in some stronger storms. However, we can`t put a lot of
stock in this so far as models have a poor track record with more
mesoscale features as of late. Beyond Thursday, guidance mostly
keeps with the near normal moisture levels across the area which
means day-to-day somewhat low-end monsoon chances are likely to
persist into at least next weekend.

The temperature forecast for the latter half of the week is also
more uncertain, at least for eastern and central Arizona where
higher chances for convection may eventually affect temperatures.
NBM/WPC forecast temperatures have only slightly started to
account for the potential increase in convection with lower desert
highs roughly a degree or two cooler for Wednesday-Friday, but
still easily high enough to keep the Extreme Heat Warning in
place. However, it definitely is plausible the warning could end
up being cancelled early across portions of Arizona if convection
increases enough later this week.

&&

.AVIATION...Updated at 1735Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns expected under few mid/high cloud
decks can be expected throughout the TAF period. The overall wind
pattern will exhibit the typical diurnal tendencies with speeds
aob 10 kts. Thunderstorms over the higher terrain areas well east
of Phoenix will likely send an outflow into the Phoenix area late
this evening, most likely moving in after 03-04Z. The outflow will
mostly serve as an easterly wind shift. No significant gusts are
anticipated and no slantwise visibility reductions from dust
expected with the outflow passage at this time.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns under some passing mid/high
cloud decks can be expected throughout the TAF period. At KIPL,
very light westerly/variable winds this morning will shift out of
the southeast early this afternoon before shifting back out of
the west early this evening. At KBLH, winds will fluctuate out of
the south to southwest. Overall wind speeds will remain aob 10
kts, although some modest afternoon/early evening gusts will be
possible. A period of light variability will be common during the
early morning hours.

&&

.FIRE WEATHER...
Above normal temperatures with fairly stable moisture levels are
expected early this week. Most lower desert communities will
reach or eclipse the 110 degree mark over the next several days.
Scattered showers and isolated thunderstorms are forecast for the
high terrain through Tuesday with an increase in monsoon activity
possible by Wednesday or Thursday. Afternoon MinRHs of 15-25% are
expected through Tuesday before increasing to 20-30% starting
Wednesday. Outside of thunderstorm winds, overall winds will
follow the typical diurnal tendencies with some modest afternoon
upslope gustiness.

&&

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

     Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Friday for
     AZZ560.

CA...Extreme Heat Warning until 8 PM PDT Friday for CAZ562-565>567-
     569-570.

&&

$$

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