Severe Thunderstorm Warning 22, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
500 PM MST Thu Aug 21 2025

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Well above normal temperatures persist through the weekend,
  resulting in widespread areas of Major to locally Extreme
  HeatRisk.

- Extreme Heat Warnings are now in effect across the majority of
  the region through the weekend.

- Strong to potentially severe thunderstorms are expected across
  portions of south-central Arizona through this evening with the
  primary threat being strong outflow winds.

- Better rain chances move into the lower deserts to end the
  workweek and even expand into SW Arizona and SE California by
  this weekend and continue into the beginning of next week.

&&

.SHORT TERM /Today through Friday/...
The main weather stories in the short term will be the continued
extreme heat persisting across the region along with increasing
thunderstorm chances as we start to get a better taste of the
monsoon season. Latest afternoon objective analysis shows the
center of the subtropical ridge of high pressure continuing to
meander over the Four Corners region with 500 mb heights remaining
around 594-596 dm. Given the persistent strength of the ridge
over the region, temperatures continue to ride well above normal
and even flirting with record highs. The temperature so far this
afternoon in Phoenix has already hit 114 degrees, which is ties
the daily record high set back in 2019. Today is expected to be
the hottest day with temperatures expected to lower around 1-3
degrees for tomorrow. The well above normal daytime highs and
morning lows has prompted widespread Major to locally Extreme
HeatRisk to persist across much of the CWA and will continue again
tomorrow. Thus, Extreme Heat Warnings remain in effect through
the end of the workweek, though many areas have now been extended
into the weekend (see long term for more details). Everyone should
continue to follow the proper heat safety precautions, including
limiting time outdoors and staying hydrated, to avoid heat-related
issues.

The largely unchanged synoptic pattern continues to bode well for
increasing monsoonal activity across our area. Latest look at the
afternoon radar shows thunderstorms firing up along the Rim over
to the White Mountains. The position of the high remains favorable
for steering thunderstorms off the high terrain toward the lower
elevations as forecast soundings show steering flow upwards of
around 15-20 kts out of the east. The environment will be more
thermodynamically conducive to support some strong to severe
thunderstorms capable of producing strong downbursts. Current SPC
mesoanalysis and forecast soundings through the rest of the
afternoon into the early evening support MUCAPE values in excess
of 1000 J/kg and inverted-V profiles with DCAPEs to around 2000
J/kg. Multiple HREF members continue to show strong support for
very strong outflow winds descending into the lower deserts as
thunderstorms progress westward/southwestward. Probabilities for
outflow gusts exceeding 35 mph are around 50-70% across south-
central Arizona through this evening with around a 10% chance of
severe gusts in excess of 58 mph. Given the threat for strong to
severe downbursts, SPC has placed portions of south-central
Arizona in a Marginal risk for damaging winds. Paintball plots
suggest thunderstorm activity may try to gravitate more toward
Pinal County as thunderstorms descend into the lower deserts and
thus they could see the greater threat for strong, damaging winds.
These strong outflow winds will also be capable of generating
dense blowing dust. Therefore, a Blowing Dust Advisory is in
effect for portions of northwest Pinal County and far southeast
portions of the metro through this evening.

The threat for strong to severe thunderstorms expands further to the
west for Friday with SPC already highlighting areas across southwest
Arizona and along the Lower Colorado River Valley in a Marginal risk
for damaging winds. Latest CAMs suggest thunderstorms developing
over the higher terrain north and east of Phoenix tomorrow afternoon
before strong outflows descend into the lower deserts. These strong
outflows are expected to progress westward into southwest Arizona
Friday evening with adequate forcing from these outflows/outflow
mergers supporting thunderstorm development. Latest HREF suggest
similar probabilities as today's for strong to severe downbursts
across a good portion of the Arizona lower deserts and over
toward the California state line. Stay tuned as we refine these
details in future updates.

&&

.LONG TERM /Saturday through Wednesday/...
Ensembles are in good agreement that the subtropical ridge will
really start to weaken and push east/southeastward Sunday night
into Monday. So, the ridge will still be overhead on Sunday,
however heights will be around 594 dm. So, while this will be
slightly weaker than the ridge today, temperatures will still be
on the warmer side. Afternoon highs are forecasted to be in the
107-111 degree range, with morning lows forecasted to be in the
mid 80s to around 90 degrees. Also, any residual cloud cover from
thunderstorm activity during the overnight hours will also help to
keep morning low temperatures on the warmer side. Due to these
warmer temperatures there is still an abundance of Major HeatRisk
across the lower deserts. Therefore, the Extreme Heat Warning has
been extended for most of the area through Saturday and through
Sunday for the Phoenix metro.

The aforementioned weakening and east/southeastward progression of
the subtropical ridge is driven by a strong trough digging into the
Great Lakes and New England regions along with a much weaker trough
digging off the Pacific coast. The aforementioned trough digging in
the eastern US will be potent enough to drop temperatures around ten
degrees below normal, making it feel like fall for much of the
eastern US. While this trough won't be moving into our region, it,
along with the aforementioned trough digging of the Pacific coast,
will dampen the subtropical ridge lowering heights aloft. So,
temperatures will cool some for our region. Currently temperatures
are forecasted to fall near normal Monday and below normal on
Tuesday and Wednesday. Current forecasted high temperatures across
the lower deserts on Tuesday and Wednesday range from the mid 90s to
low 100s.

The E/SE shift in the subtropical high will cause the flow overhead
to become more SE/S. This will shift better PoPs into the south-
central AZ lower deserts, including the Phoenix Metro. Ensembles
disagree on the PWATs for the beginning of next week (GEFS shows 1.3-
1.6" and the ECMWF ensemble shows 1.5-1.8") either way there will be
ample moisture to support shower and storm activity across the
region. The big question right now is just how much shower and
thunderstorm activity will there be. NBM PoPs are still running hot
(around 40-70% across much of the CWA) so PoPs have been lowered
some (around 20-50% across much of the CWA). With daily thunderstorm
chances, each day's activity will depend on how the previous day
shakes out.

&&

.AVIATION...Updated at 2359Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Abrupt wind shifts with gusty outflow winds will be the primary
weather hazard early this evening. Thunderstorms to the east and
northeast over the mountains will send an outflow or multiple
outflows into the Phoenix area terminals this evening. Favored
timing is 01-03Z with E/NE gusts most likely in the 20-30kt range,
but there is potential for higher gusts with 5-10% odds of a peak
gust greater than 50 kts. These winds will be capable producing
lofted dust and potential visibility restrictions, with the best
potential at KIWA. A large dust storm cannot be ruled out should
strong winds move W/NW across northern Pinal County. At this time,
there is less than a 30% chance of SHRA/TSRA directly impacting
any terminal, and have maintained a VC mention through midnight.

There is potential for impactful conditions again Friday, but
early indications are that RA/TS may skip over the Phoenix
terminals to the west tomorrow with potential outflows from the
SW and/or NW in the evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist into Friday under passing
mid/high cloud decks. Wind trends will be similar to the past 24
hours with directions generally varying between SE and SW. Periods
of variability or nearly calm conditions will be common during
the morning hours.

&&

.FIRE WEATHER...
Well above normal temperatures continue today and tomorrow as highs
approach record levels and lows approach record warm levels.
Scattered thunderstorm activity is expected across the higher
terrain today, with isolated chances across the lower deserts of
south-central AZ. Tomorrow and through the weekend will see
increasing shower and storm chances across the western districts.
Daily shower and storm chances will continue into the beginning of
next week. Strong gusty and erratic winds are expected with any
thunderstorms. Otherwise, winds will follow their typical
upslope/downvalley patterns with afternoon gusts in the teens.
Relative humidity will bottom out around 15-25% through the weekend,
increasing to 20-30% for the beginning of next week. Overnight
recovery will be poor across the western districts and fair across
the eastern districts through the end of the workweek, increasing
to fair area wide this weekend.

&&

.CLIMATE...

Record highs later this week:

Date       Phoenix          Yuma          El Centro
----       -------          ----          ---------
8/21     114 in 2019     115 in 1969     117 in 1969
8/22     113 in 2011     115 in 1969     117 in 1969

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Saturday for AZZ530>536-538-
     539-541-545-547-549-552>555-559.

     Extreme Heat Warning until 8 PM MST Sunday for AZZ537-540-
     542>544-546-548-550-551.

     Blowing Dust Advisory until 9 PM MST this evening for AZZ550-551-
     553-554.

     Extreme Heat Warning until 8 PM MST Friday for AZZ556-560-562.

CA...Extreme Heat Warning until 8 PM PDT Saturday for CAZ560>570.

&&

SHORT TERM...Smith
LONG TERM...Berislavich
AVIATION...Benedict/Frieders
FIRE WEATHER...Berislavich
CLIMATE...18

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