249
FXUS65 KPSR 291010
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
310 AM MST Sat Aug 29 2026

.KEY MESSAGES...

- Extreme Heat Warnings go through early this evening before a
  noticeable cool down begins Sunday.

- A Flood Watch has been issued for south-central Arizona from
  late this afternoon through Saturday night. Localized rainfall
  amounts of up to around two inches will be possible.

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

- Near to below normal temperatures are forecast starting Sunday
  before warming again during the latter part of next week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
Despite the extreme heat still being present through this
afternoon, it will quickly come to an end by Sunday as everything
is pointing toward an active period of weather starting late this
afternoon. The subtropical ridge is currently in a weakening
phase while also slowly shifting eastward through New Mexico. The
placement of the ridge is allowing for modest moisture advection
into Arizona with 1"+ PWATs now covering all but far
eastern/northeastern parts of the state to as high as 1.6" across
the southwest portion. Low level moisture has so far been slow to
increase, but we are expecting low level mixing ratios to increase
to around 10 g/kg by late this afternoon and 11-12 g/kg by early
Sunday.

In addition to the increase in moisture, the upper levels will
become much more conducive for storm development by later today
as a Pacific trough noses into our region from the northwest.
Forecast soundings for south-central Arizona by late this
afternoon show a mostly uncapped environment with MUCAPEs between
1000-1500 J/kg and very high DCAPEs of 1500-1800 J/kg. The only
ingredient lacking for severe weather for today will be good
shear. However, even without good wind shear we are expecting to
have enough instability, high DCAPEs, and upper level support for
some strong to possibility severe storms to develop. HREF guidance
hints at a couple different areas supporting a strong to severe
wind threat today, one over the Imperial Valley and the other
centered over Pinal into Maricopa Counties. CAMs favor storm
development first across Pima County late this afternoon before
shifting northward with further development expected into south-
central Arizona. The strong to severe wind threat should mainly
fall between 5-10 pm this evening before transitioning to mostly a
heavy rainfall/flood only threat from late evening into the
overnight hours.

The amount of instability and upper level support available is
likely to allow for a few rounds of showers and thunderstorms
later today and tonight and this is where the heavy rainfall and
flood threat stems from. Moisture levels are not expected to be
all that much above normal, but they will be plenty adequate to
support rainfall rates of 1.5-2.5"/hour with the strongest storms.
Training of storms may also be an issue, especially over higher
terrain areas. The heavy rainfall/flood threat is high enough for
us to issue a Flood Watch from late afternoon through 5 AM Sunday
morning across Maricopa, Pinal, and Gila Counties with the peak of
the event likely occurring during the evening hours.

Sunday is still looking quite good for storm potential with
moisture improving slightly over today, while the peak of the
upper level support is expected to be in place over Arizona.
Sunday morning and even a good portion of the afternoon may be a
recovery period after the activity from today/tonight, but models
show enough sunshine for instability to become surface based again
by late afternoon with MUCAPEs again reaching 1000-1500 J/kg. The
strong to severe wind threat for Sunday should again be present,
but likely not to the degree of what is expected today. Assuming
the atmosphere can recover enough, chances are we will face
another round of localized heavy rainfall and flood potential from
late Sunday afternoon through Sunday evening. This is reflected by
the slight risk on WPC`s Day 2 ERO.

&&

.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 1009Z.

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

The main aviation concern will be thunderstorms and gusty
outflows, late this evening and into the overnight period. Before
then, typical diurnal tendencies are expected. Models continue to
point towards an active night with a southerly to southeasterly
gusty outflow with gusts between 25-30kts possible. Hi-res
guidance shows storms popping up as early as 22-23Z but not over
fully over the terminals until closer to 01-03Z. A PROB30 remains
reflected the TAFs for in all terminals for thunderstorms however
the exact timing continues to be challenging and may be subject
to change as we get close to the event tonight. Any outflows from
the S/SE would also bring BLDU/HZ with them, mostly expected to
impact KPHX and KIWA. Winds are currently forecasted to settle
back out of the east for the overnight period, once storms
subside, but they could remain highly VRB until morning. Mostly
SCT mid/high cloud decks will be common through the period, with
the lowest CIGs forecasted at 10kft.

Southeast California/Southwest Arizona including KIPL and KBLH:

The main aviation concern is a chance for thunderstorms this
evening at KIPL. Before then winds will tend to follow their
typical diurnal patterns. Oscillating between southerly and
southwesterly at KBLH and southeasterly to westerly at KIPL,
favoring a westerly component for a majority of the period. Wind
speeds will generally be aob 10 kt, with some gusts up around 20kt
expected tomorrow afternoon at both terminals. A PROB30 is
reflected in the TAFs for KIPL for TS from 23-01Z tonight, but the
main concern will be the increase in gust speeds during that
timeframe. KIPL can expect gusts between 25-30kts with some
outlier Hi-res guidance suggesting higher at times, but based on
last nights evens not impossible to see gusts upwards of 35kts
once more for a short period. Otherwise, FEW-SCT mid/high cloud
decks will be common throughout the period.

&&

.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.

     Flood Watch from this afternoon 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...Kuhlman
LONG TERM...Kuhlman
AVIATION...Ryan
FIRE WEATHER...Kuhlman