862
FXUS65 KPSR 300000
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
500 PM MST Sat Aug 29 2026

.UPDATE...Updated 00Z Aviation Discussion.

&&

.KEY MESSAGES...

- Extreme Heat Warnings remain in effect through early this
  evening as afternoon high temperatures approach the 110 degree
  mark across the lower deserts.

- Showers and thunderstorms, some potentially strong to severe,
  are expected from later this afternoon into tonight. Additional
  rounds of showers and storms are also possible Sunday and
  Monday.

- A Flood Watch remains in effect for south-central Arizona from late
  this afternoon through tonight as heavy rainfall, producing
  localized amounts in excess of 1-2 inches leading to flash
  flooding, will be possible.

- Near to slightly below normal temperatures are expected starting
  Sunday and lasting into the first half of next week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
Latest water vapor satellite imagery as well as objective analysis
depict the subtropical high displaced east of the region,
centered across eastern New Mexico into western Texas, as a broad
upper trough is encompassing much of the west coast. This overall
pattern configuration is resulting in a southerly wind flow,
which is aiding in moisture advection across much of the region.
The latest SPC Mesoanalysis shows PWATs in excess of 1"+ across
much of Arizona with values in excess of 1.5" covering much of the
lower deserts of south-central and southwest Arizona, allowing
low-level mixing ratios to reach 10+ g/kg.

The increased moisture levels and MUCAPE values of around 1000
J/kg combined with some increased upper-level forcing for ascent
from the aforementioned west coast trough will support a
favorable environment for widespread storm activity heading into
this afternoon and tonight across much of south-central AZ with
much more isolated activity (10-20% chance) near the Imperial
Valley and portions of La Paz County. Latest HREF guidance is in
decent agreement that activity this afternoon will develop across
the AZ High County as well as across southeast AZ, with the
potential for multiple outflows to materialize. Latest forecast
soundings for late afternoon/early evening hours show a nearly
uncapped atmosphere and thus it will not take much low-level
forcing to spark storms across the lower deserts with a singular
outflow likely sufficient to cause convective initiation. With
DCAPE values expected to peak at around 1500-1800 J/KG, any
thunderstorms will be capable of producing strong to severe
downburst wind gusts and thus, generate strong outflows. Latest
HREF neighboring probabilities show a 50-70% chance of winds
exceeding 35 mph with around a 10% chance of winds reaching severe
levels (i.e. greater than 58 mph) across much of south-central
AZ. With the potential for a strong outflow to materialize from a
storm complex that is likely to develop across southeast AZ,
significant blowing dust will be a possibility as well across
Pinal County into at least southern portions of the Phoenix Metro
Area. Given this potential, in coordination with WFO Tucson, a
Blowing Dust Advisory has been issued between 4 PM and 9 PM MST
for these areas. In addition to the strong winds and blowing dust
potential, heavy rainfall leading to flash flooding will also be a
concern as there is a potential for training of storms,
especially across the higher terrain areas. Given this potential
for flash flooding, a Flood Watch is in effect from late this
afternoon through tonight across much of south-central AZ.

Heading into Sunday, conditions will remain favorable for additional
storms affecting much of south-central AZ once again as an upper-
level jet streak moving through the Great Basin will increase the
upper-level divergence and thus the upper-level forcing for ascent.
The main question and uncertainty for how active Sunday turns out to
be is the degree of recovery from the convective activity expected
later today. However, if the atmosphere is able to recover enough,
then another very active day is likely as MUCAPE values are
forecast to exceed 1000 J/KG with scattered to numerous
thunderstorms capable of producing strong wind gusts, areas of
blowing dust, and heavy rainfall leading to flash flooding all on
the table once again.

With 500 mb height fields still hovering around 594-596dam today,
another day with highs near to just above 110 degrees can be
expected across much of the lower desert communities, resulting
in the continuation of Major HeatRisk. Therefore, the Extreme Heat
Warning remains in effect through 8 PM MST. The further lowering
of the upper-level height fields as the ridge shifts further east
into the southern Plains on Sunday will cause afternoon high
temperatures to cool 3-6 degrees, with readings ranging in the
low to mid 100s across the south-central AZ lower deserts and mid
to upper 100s across the western deserts. This will be enough to
cause HeatRisk levels to drop into the moderate category and thus
put an end to the prolonged extreme heat episode that has been in
place for more than a week.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Model uncertainty remains quite high for much of next week,
especially on Monday as at least the eastern half of Arizona
should retain good moisture, while an upper level low swings
through Nevada during the first part of the day. We are still
unsure how much instability will be present and if the low will
move to the north too quickly, but guidance is still favoring
30-60% PoPs from Phoenix and areas to the east of Phoenix for
much of Monday. Monday is likely to be very conditional on any
strong to severe storm threat due to the question of instability,
but we are expecting better wind shear on Monday. The passing
trough to our northwest should also begin to sweep drier air
through a good portion of our area on Monday, but this may only
impact western areas during the first part of the day leaving
enough moisture from Maricopa County eastward. This drying and
the eventual loss of upper level support is likely to mostly end
rain chances on Tuesday before returning by next Wednesday or
Thursday. Guidance suggests the tropics across the eastern Pacific
will remain very active next week likely leading to more moisture
getting advected into the Desert Southwest during the latter half
of next week. Forecast temperatures are shown returning into or
even a few degrees below the normal range early next week before
rising midweek as conditions temporarily dry out. The subtropical
ridge is also expected to nudge back into our region from the east
helping to boost temperatures back to or a few degrees above
normal at some point late next week.

&&

.AVIATION...Updated at 0000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

The main aviation concern will be two periods of thunderstorms,
gusty outflows,and blowing dust. One this evening and another one
again tomorrow evening. A few isolated showers and thunderstorms
have popped up within the Phoenix Metro this afternoon. Some more
isolated showers and storms could continue to pop-up, however,
better chances for activity arrive after 02Z this evening. We are
anticipating a south/southeasterly outflow from the activity down
towards Tucson, most likely to arrive around 03-05Z. This will
help initiate additional storms. This outflow would also bring
BLDU/HZ and reduced visibility. It is still unsure how strong this
outflow and how dense the dust would be. All shower and
thunderstorm activity is expected to be NE of the terminals by 06Z
this evening. Winds will then return to their diurnal trends with
southeasterly winds overnight and west/southwesterly winds
tomorrow afternoon. Another period of VCTS/TSRA is expected
tomorrow night. Best timing right now looks to be after 02Z.
Mostly SCT mid/high cloud decks will be common through the
period, with the lowest CIGs forecasted at 10kft during
thunderstorm activity.

Southeast California/Southwest Arizona including KIPL and KBLH:

At KIPL, current southwesterly winds will go southeasterly early
tomorrow morning with wind speeds aob 10 kt. At KBLH, winds will
fluctuate between southwesterly and southerly through the TAF
period. Wind speeds will be elevated (10-15 kt) the whole period
with some gusts of 20-25kt during the afternoons and early
evenings. FEW-SCT mid and high clouds will be common.

&&

.FIRE WEATHER...
A pattern shift this weekend will lead to increasing moisture and
very good chances for showers and thunderstorms across the eastern
districts. Gusty winds, heavy rainfall, and localized flooding
will all be possible across south-central Arizona beginning late
this afternoon. The western districts will generally stay dry.
Expect MinRHs of 15-20% today areawide before rising to 25-35%
across the eastern districts starting Sunday. Temperatures are
also forecast to drop to near normal readings starting Sunday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ530>555-
     559-560.

     Blowing Dust Advisory until 9 PM MST this evening for AZZ539-550-
     551-553-554-559.

     Flood Watch through late tonight for AZZ534-537-538-540>563.

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

&&

$$

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