051
FXUS65 KPSR 211115
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
415 AM MST Thu Aug 21 2025

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- Near record temperatures will continue today and tomorrow
resulting in the continuation of widespread Major HeatRisk, with
localized Extreme HeatRisk.

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

- Scattered thunderstorm activity will be across the higher terrain
with isolated thunderstorms extending into the lower deserts this
afternoon and evening; main threats will be strong gusty winds,
lightning, and localized heavy downpours.

- 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 Saturday/...
Early this morning the synoptic pattern remains largely unchanged
from the past couple of days. The RAP analysis shows the subtropical
ridge still centered over the Four Corners region, with a strength
of 596 dm. The strength of the ridge is expected to fluctuate around
596-597 dm today and into tomorrow. With the strength of the ridge
being similar to slightly stronger than yesterday, temperatures the
next couple of days will also be similar to slightly warmer than
yesterday. Afternoon high temperatures are forecasted to be around
109-116 degrees across the lower deserts and around 100-108 degrees
across the higher terrain. Morning low temperatures will also be on
the warmer side with lows forecasted to be in the upper 80s to low
90s across the lower deserts and in the upper 70s to low 80s across
the higher terrain. Morning lows could potentially be warmer than
currently forecasted, depending on residual cloud cover from any
thunderstorm activity. The combination of these morning low and
afternoon high temperatures will result in the continuation of
widespread Major HeatRisk with localized areas of Extreme HeatRisk.
Thus, an Extreme Heat Warning remains in effect through Friday
evening. Everyone should exercise the proper heat safety
precautions, including staying hydrated and limiting time outdoors,
to avoid heat-related health issues. Ensembles do show the ridge
weakening slightly (594-596 dm) Friday into Saturday. This will
result in temperatures cooling only a few degrees. Even with
temperatures cooling a few degrees a large area of the lower deserts
remains in the Major HeatRisk category on Saturday. Due to this the
Extreme Heat Warning may need to be extended into the weekend.

With the position of the high largely remaining unchanged, it
remains in a favorable position to promote increasing monsoonal
activity. According to the SPC mesoanalysis, PWAT values remain in
the 1.3- 1.5" range across the CWA. Models also show MUCAPE values
being around 1000 J/kg this afternoon and evening. The combination
of the moisture and instability will promote scattered shower and
thunderstorm activity across the higher terrain in eastern AZ,
including southern Gila County this afternoon and evening. The main
threats with these storms will be strong gusty winds, lightning, and
localized heavy downpours. Strong gusty outflow winds will be the
main threat as models show DCAPE values around 1000-1500 J/kg, or
higher, this afternoon and evening. The HREF shows a greater than
70% chance for winds in excess of 35 mph across southern Gila,
eastern Maricopa, and Pinal Counties. The HREF also shows an area of
10% chance of winds in excess of 58 mph across Pinal County. With
better moisture over the Phoenix Metro area, and more potent outflow
boundaries expected this evening, there is around a 20% chance of
showers and storms across the Phoenix Metro. Similar to last night,
the strong gusty winds expected this evening are expected to lead to
areas of blowing dust, particularly on the south side of the Phoenix
Metro.

Water vapor satellite imagery shows a punch of dry air moving
westward into our area from the Plains. This will push the better
moisture into SW AZ and SE CA for Friday and Saturday. Ensembles
also continue to show the center of the subtropical high migrating
westward on Friday and Saturday as well. This set up will lead to
better monsoonal activity across SE CA and SW AZ (20-40%; upwards of
50-60% across Joshua Tree National Park), leaving more of a donut
hole over the Phoenix Metro, however chances are still around
20-30% across the Phoenix Metro. Again, the biggest threats will
be strong gusty winds, lightning, and localized heavy downpours.

&&

.LONG TERM /Sunday 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 and therefore the Extreme Heat Warning may need to
be extended through the weekend.

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 1115Z.

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. Confidence is good that E/SE
winds will switch to a light westerly component early/mid afternoon
under mid/high cloud decks. Thunderstorms over eastern AZ mountains
should send at least one outflow boundary into the Phoenix area
terminals this evening with modest uncertainty in timing and
magnitude of gustiness. Regardless, E/NE gusts 20-30kt will be
possible with areas of lofted dust and potential visibility
restrictions. At this time, there is less than a 30% chance of of
SHRA/TSRA directly impacting any terminal, and have only indicated a
VC mention for the time being.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Friday morning 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 Friday for AZZ530>556-559-
     560-562.

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

&&

$$

SHORT TERM...Berislavich
LONG TERM...Berislavich
AVIATION...18
FIRE WEATHER...Berislavich
CLIMATE...18