244
FXUS65 KPSR 170516
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1015 PM MST Sun Aug 16 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES....

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

- Extreme Heat Warnings will be take effect Monday and continue
through Friday with widespread Major HeatRisk.

- 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/...
A weak shortwave trough moved through this morning, within the
southwest flow, and helped drive some virga showers across the area.
Midlevel water vapor shows dry air moving in on the back side of
this feature, which will continue to spread across the area through
tonight and add a dry subsident layer at and above 500mb heading
into Monday. Convection this afternoon will mostly be limited to the
high terrain of northern and eastern AZ with relatively weak
updrafts due to minimal instability. Heading into Monday, a low
pressure feature slowly moving through Chihuahua, MX looks to come
just close enough to shift mid-level steering winds to more of a NE
component, albeit weak, across southeast AZ, including the White
Mtns. This change, in addition to slightly better instability, may
be enough for gusty outflow winds to move west/southwest out of the
White Mtns toward South-Central AZ in the late afternoon and
evening. All members of the latest HREF show an outflow, of varying
strength and timing, moving through southern Gila, Pinal, and
Maricopa counties Monday evening. A trend of evening outflows into
the lower deserts may continue Tuesday (and beyond) as moisture and
instability nudge up slightly. Synoptically, mid-level steering
winds become more easterly across all of southern AZ Tuesday as the
low pressure feature drops southwest through Sonora, MX and the
subtropical anticyclone positions near/over the AZ-NM border.

Unseasonably hot and extreme temperatures will be the primary
sensible weather impact through the start of the workweek as high
pressure strengthens over the area through Monday. Current objective
analysis shows 500mb heights are around 594-595dam, but will rise up
to 596-597dam by Tuesday, which is at or above the 97th percentile
of climatology for this time of the year. High temperatures today
will be around 1-3 degrees above daily averages, with lower deserts
reaching 105-109 degrees. Temperatures then warm a few degrees into
Monday and Tuesday, increasing up to 4-6 degrees above averages and
coming within a few degrees of daily records. This does mean a
return of temperatures reaching or exceeding 110 degrees across the
lower deserts. These hot afternoon temperatures combined with early
morning lows in the mid 80s to 90 degrees will result in scattered
to widespread coverage of Major HeatRisk starting Monday, which is
when an Extreme Heat Warning will take effect.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/....
The subtropical high will 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 with Extreme Heat
Warnings currently in effect through Friday evening. Extension of
this warning may be warranted through next weekend as a weakening
and slight re-positioning of the high further away may not come
until Sunday-Monday next week.

The latest guidance does show the high eventually moving northeast
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 monsoon 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 will be most active as it will be
dependent on mesoscale processes such as outflow evolutions and/or
any easterly waves, which are difficult for models to resolve
several days out. As of right now, NBM PoPs across the south-central
AZ lower deserts starting next Thursday range between 10-30%.

&&

.AVIATION...Updated at 0515Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather concerns will exist through Monday night under a
few mid/high cloud decks, though uncertainty regarding timing of
wind shifts continues. Confidence is good that winds will take
longer to complete the typical overnight easterly switch, though
prolonged periods of light and variable winds may be common Monday
morning. Forecast confidence is increasing that storms over
mountains east of Phoenix early Monday evening will send an easterly
outflow boundary and abrupt wind shift into the metro by mid
evening.


Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through Monday night under mostly
clear skies. Winds will behave similarly to the past 24 hours
including periods of light and variable character late night/early
morning.

&&

.FIRE WEATHER...
Near to slightly above normal temperatures are expected this
afternoon and then will rise another few degrees into the coming
workweek. Most lower desert communities will reach or eclipse the
110 degree mark each day this week. Minimal 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 as moisture increases. Afternoon
MinRHs through most of the week will 15-25% and overnight recoveries
will be around 35-50%, highest in the Imperial Valley to Yuma, AZ.
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...Benedict
LONG TERM...Lojero/Benedict
AVIATION...18
FIRE WEATHER...Lojero/Benedict