610
FXUS65 KPSR 201057
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
357 AM MST Thu Aug 20 2026

.UPDATE...Updated 12Z Aviation Discussion.

&&

.KEY MESSAGES...

- Lingering showers and thunderstorms are expected through around
  sunrise this morning across south-central Arizona followed by
  some isolated storms in the afternoon over high terrain areas.

- After a brief reprieve from the extreme heat today over south-
  central and eastern Arizona, highs will return to around 110
  degrees by Friday, lasting into early next week.

- Extreme Heat Warnings are in effect through Sunday evening due
  to continued areas of high-end moderate to major HeatRisk.

- Thunderstorm chances will dip starting Friday, likely remaining
  confined to the Arizona high terrain through at least Saturday.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...
It is amazing what can happen when the lower deserts finally gets
a virtually uncapped atmosphere. Models were showing the
potential for a significant outflow along with scattered storms
developing into the south-central Arizona lower deserts, but there
wasn`t a strong consensus on its evolution. Yesterday was just
one of those days where everything came together perfectly for a
large MCS to develop and to produce fairly widespread strong to
severe winds. Many locations within and around the Phoenix area
reported wind gusts between 50-60 mph with a few reports around 65
mph. The afternoon balloon launches for KPHX both showed
1500-1800 J/kg of CAPE with similar values of DCAPE, while CIN was
low enough to be easily overcome from a modest to strong outflow.
The convection over the high terrain became organized enough to
persist into the lower deserts with additional development
occurring once the CAP was broken. The storms are even
redeveloping early this morning along a mid-level convergent line
from Phoenix to Show Low. Hi-res CAMs somewhat show this line of
convection, but they have no idea how long it may last. Any
training of storms within this southwest to northeast line could
result in localized additional rainfall amounts of up to an inch
through 4 AM. We anticipate this activity to gradually wind down
by sunrise.

The rest of today is likely to be much more quiet as the
atmosphere was effectively overturned by the widespread storm
activity. Temperatures have cooled substantially with readings
into the 70s over portions of the south-central Arizona lower
deserts. Cloud cover is also expected to linger through a good
portion of this morning, potentially keeping daytime highs from
even reaching 105 degrees in the Phoenix area. Hi-res CAMs are
finally catching on to the overturned atmosphere showing mostly
scattered convection along the Mogollon Rim through southern Gila
County this afternoon, but then dissipating before moving into the
lower deserts. Have adjusted PoPs to around 10-15% in the Phoenix
area to account for the more stable environment. Little has
changed with the western lower deserts with temperatures remaining
quite hot with elevated dew points. Forecast highs of 109-112
degrees are expected across southwest Arizona and southeast
California with even higher heat indices.

The subtropical high center is favored to shift east
northeastward into Colorado on Friday and then potentially wobble
southeastward into eastern New Mexico and/or into western Texas by
Sunday. The expected shift in the high should turn winds out of
the south ushering in drier air Friday into Saturday. Guidance
shows enough drying to push low level mixing ratios to 9-10 g/kg
on Friday to as low as 7-8 g/kg on Saturday. PoPs for both Friday
and Saturday drop to below 10% for the lower deserts to 10-20%
over portions of the high terrain. There is some guidance showing
more convection forming near the Mexico/Arizona border on Friday,
so we can`t rule out some sort of outflow emanating northward
into our area Friday evening.

Temperatures will also recover by Friday with daytime highs
topping out at or just above 110 degrees across the lower
deserts. Forecast dew points are also shown to decrease closer to
50-55 degree range by Saturday lowering heat indices closer to 110
degrees.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Model uncertainty remains quite high for the first half of next
week as the position of the high is likely to set up somewhere
over eastern New Mexico and western Texas by Monday with little to
no movement into the middle of next week. This position can cause
higher uncertainty in moisture levels for our area with the
latest guidance trying to advect some moisture into our area by
Sunday or Monday, but NBM forecast PoPs are at most 10-15% for the
lower deserts. At this point, we could continue to see mostly
slight chances favoring the high terrain into early next week, but
if moisture does eventually improve enough storm chances are
likely to be higher than what the NBM is depicting. Another
wildcard will be the potential influence of an upper level trough
that may attempt to move into western portions of our region
Sunday into Monday. If this occurs, it may be enough to improve
convective potential across southeast California and western
Arizona for Sunday and/or Monday.

Temperatures are expected to continue to be more influenced by the
strong subtropical high as H5 heights hover between 593-596dm
across the Desert Southwest through early next week. Daytime highs
are not expected to change much day to day from Sunday through
early next, barring any significant change with the convective
chances. The Extreme Heat Warning is currently in effect through
Sunday, but it seems quite likely it will need to be extended
again at some point.

&&

.AVIATION...Updated at 1055Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Lingering rain and a few isolated thunderstorms continue across
the Phoenix Metro early this morning. All activity is expected to
exit the Metro over the next 1-2 hours. Then, dry conditions are
expected through the rest of the TAF period. Winds will be light
and variable this morning (but may tend to favor a SE component)
prior to developing the usual westerly component this afternoon.
The main aviation concern will be on if any outflows can make it
into the Phoenix Metro. Current hi-res models show a NE outflow
approaching the Phoenix Metro, but models differ on the exact
strength of this outflow and how far it will survive into the
Valley. As of now, I have added this outflow in as a FM group for
KDVT and KSDL but have left it as a TEMPO at KPHX and KIWA. Then,
SE winds are expected overnight and through tomorrow morning. SCT-
BKN cloud decks with bases as low as 10 kft are expected through
the majority of the TAF period. A period of only FEW clouds is
expected this afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected during the next 24
hours. At KIPL, SSE winds will continue before going W this
evening. Wind speeds will generally be aob 10 kt. At KBLH, winds
will be light and variable this morning before developing a S
component by the mid morning hours. A brief period of SW winds is
expected tomorrow evening before going back S overnight. Winds
will be aob 15 kt. FEW-SCT cloud decks will be present through
much of the forecast window, with the lowest bases around 15 kft.

&&

.FIRE WEATHER...
Elevated moisture levels will persist today with a temporary
reprieve from the extreme heat across the eastern districts.
Expect mostly isolated showers and thunderstorms this afternoon
and early evening over the high terrain areas. Drier air will then
work its way in for Friday and Saturday with even lower chances
for rain while temperatures heat back up to extreme levels.
MinRHs of 20-30% today will lower to 15-25% beginning Friday.
Winds should overall follow the typical diurnal tendencies with
some modest afternoon upslope gustiness.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530>544-546-
     548>551-553>555-559-560.

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

&&

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Berislavich
FIRE WEATHER...Kuhlman