975
FXUS65 KPSR 160803
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
103 AM MST Sun Aug 16 2026

.KEY MESSAGES....

- As high pressure builds over the region through the upcoming
  week, temperatures will heat up several degrees above normal
  levels as lower desert highs climb above 110 degrees.

- Extreme Heat Warnings will be in effect throughout the week as
  widespread Major HeatRisk materializes.

- Thunderstorm activity through the majority of the upcoming week
  will be mostly confined to the Arizona High Terrain and
  southeast Arizona.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
Latest objective analysis continues to indicate southwest flow
aloft entrenched across much of the Desert Southwest as general
trofiness persists to the northwest while the subtropical high is
positioned near the south-central states. The southwest flow will
continue to advect drier air into the region. Thus, mainly quiet
weather with no convective activity can be expected across the
forecast area for today. With 500 mb heights rising slightly from
the previous couple of days, afternoon high temperatures across
the lower deserts will top out in the mid to upper 100s.

The subtropical high will gradually build over the region during the
first half of the week. As the high begins to build, 500 mb heights
will rise closer to 594-596dam, which will represent the 97th
percentile of climatology for this time of the year. Therefore,
temperatures will climb another 3-5 degrees through Tuesday with
afternoon highs breaching the 110 degree mark across the lower
deserts. These afternoon high temperatures combined with early
morning lows in the mid to upper 80s will result in a major
spatial expansion of the Major HeatRisk Category and thus the
Extreme Heat Warnings will start to go into effect across all the
lower deserts starting Monday and for the San Carlos area in
southern Gila County starting Tuesday. Convective activity during
the first half of the week, will be mainly confined to the
eastern and southeastern third of AZ with very little to no
activity expected elsewhere given the below normal moisture values
that will be in place, resulting in little to no instability.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/....
The subtropical high will continue to remain entrenched across the
region through at least the end of the week, with 500 mb height
fields remaining steady between 595-597dam. Therefore, temperatures
will continue to run a good 4-7 degrees above normal as afternoon
highs across the lower deserts will range between 108-113 degrees.
There will also be little overnight relief as an increase in low-
level moisture will cause overnight lows to only bottom out
between the mid 80s to low 90s with the low 90s expected in the
Phoenix area. Therefore, widespread Major HeatRisk will continue
to remain in place with Extreme Heat Warnings in effect through
Friday evening.

The latest guidance does show the high eventually moving
northeastward into the Four Corners region by the end of the week
into next weekend, putting the region under a more favorable
moisture advection pattern as the east to southeast flow
increases. Therefore, an increase in monsoonal activity is more
likely during this timeframe, mostly across the higher terrain
areas. Although, it will certainly be possible for convective
activity to impact the south-central AZ lower deserts at some
point as well, it is still too far out to know what days could be
active as it will be dependent on mesoscale processes such as
outflow evolutions and/or any easterly waves that are difficult to
pinpoint several days out. As of right now, NBM PoPs across the
south-central AZ lower deserts starting next Thursday range
between 10-20%.

&&

.AVIATION...Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Sunday night under
periods of thick 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 during the typical wind shifts.

Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through Sunday night under occasional
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...
Near normal temperatures will prevail today before rising above
normal starting Monday. Little to no monsoon activity is expected
through the first half of the week, with only a few isolated
thunderstorms expected across the far eastern districts.
Thunderstorm chances increase somewhat, mainly for south-central
AZ, by the latter half of the week. Afternoon MinRHs during the
next several days will range between 15-20% across the lower
deserts and 20-25% across the far eastern districts. Outside of
thunderstorm winds, the overall winds will follow the typical
diurnal tendencies with some modest afternoon upslope gustiness.

&&

.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.

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

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

&&

$$

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