361
FXUS65 KPSR 010515
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1015 PM MST Mon Aug 31 2026

.UPDATE...06Z Aviation Discussion

&&

.KEY MESSAGES...

- Chances for showers and thunderstorms will continue through
  early this evening, mainly west of Phoenix, with Flood Watches
  in effect.

- Quiet weather under mostly clear skies is expected for Tuesday
  and Wednesday before potentially another more active period of
  weather materializes by the end of the week into the weekend.

- Near to slightly below normal temperatures are expected
  throughout much of the week.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Latest water vapor satellite imagery shows a well-defined upper-
level shortwave over southern Nevada and is the main feature that
drove the widespread rainfall activity that was observed across
much of south-central AZ throughout the morning hours. Rainfall
intensity has been on the light to locally moderate side and thus
rainfall accumulations for the most part have remained under 0.3",
with some localized areas observing amounts up to 0.5". Most of
this activity has moved east of Phoenix and will be ending in Gila
County during the early afternoon hours. The overworked atmosphere
from the morning activity will essentially end the potential for
more organized convective activity for the rest of today for
much of south-central AZ. The main focus for convection for this
afternoon will shift west of Phoenix, across portions of La Paz
into northern Yuma County as well as western Maricopa County as
ample heating will cause MLCAPE values to peak at 1500-2000 J/KG,
which is more than sufficient for strong thunderstorms to develop.
Although strong downburst wind gusts will be possible, the
primary hazard will be heavy rainfall leading to flash flooding
with localized amounts in excess of 1-2" possible, especially with
any training cells. As the upper-level shortwave lifts
northeastward into Utah by this evening, much of the upper-level
support will be lifting to the north as well and thus activity
should diminish by the early evening hours with quieter conditions
expected during the late evening and overnight hours tonight.

Quieter weather is expected Tuesday and Wednesday as significantly
drier air due to west-southwest mid-level flow will overspread the
region, especially in the mid to upper levels with strong subsidence
aloft. A few isolated storms will still be possible Tuesday
afternoon, mainly across the terrain escarpments given that
boundary level moisture will still be sufficient with mixing
ratios above 10 g/kg. However, by Wednesday, mixing ratios will
have dropped to less than 10 g/kg with little to no instability
expected and thus storm chances should be completely eliminated
across much of the CWA.

Due to the abundant cloud cover and rainfall this morning, afternoon
high temperatures across much of south-central AZ will likely
struggle to reach 90 degrees while significantly warmer highs due to
more sunshine can be expected across the western deserts as readings
top out in the mid to upper 100s. Temperatures Tuesday and
Wednesday, with much more sunshine, should rebound into the low 100s
across the south-central AZ lower deserts and top out into the mid
100s across the western deserts, with these readings near to a few
degrees below normal for early September.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Forecast concern is increasing for the potential of tropical
moisture surging northward into the region as early as Thursday
night into Friday, but more so for the coming weekend. NHC shows a
tropical disturbance currently near 10N and 107W with a 90%
chance of cyclone formation this week and likely tracking
northward off the coast of Baja by Friday into the weekend. There
is still a lot of uncertainty with this potential tropical
system, but model guidance has been coming to a bit better
consensus the last several model runs. Roughly 90% of the GEFS and
EPS members now show PWATs increasing to 1.8-2.2" over portions of
our area by Friday or Saturday. Given this likely increase in
moisture, PoPs have gone up starting Friday and continue through
the weekend. It will likely be at least 2 or 3 more days until we
have a good idea on what would likely happen late this week.
Getting tropical moisture into our region is definitely not
unusual, but many times when it happens we struggle to build
instability due to extensive cloudiness and poor lapse rates.
However, it seems quite likely a Pacific trough will be situated
along or just off the West Coast which may provide for enough
upper level forced ascent to overcome the likely lackluster
instability. We will continue to watch this throughout the week as
it very well could lead to another round of heavy rainfall at
some point.

&&

.AVIATION...Updated at 0515Z.

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

No major aviation concerns are expected during the TAF period.
Winds will return to following light and diurnal trends with
variability during directional shifts. There are hints of an
isolated afternoon VCTS and later evening outflow, but current
chances for either of these events is around 10% or less and
therefore have been excluded from the TAFs. Other than a FEW low-
level bases around 7-10 kft, skies will be mostly clear.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected during the TAF period.
Winds will follow familiar diurnal trends with perhaps some
variability occurring during directional switches. Other than a
FEW bases around 10 kft, skies will be mostly clear.

&&

.FIRE WEATHER...
Lingering light showers will persist across the far eastern
districts through early this afternoon with scattered showers and
storms across portions of southwest Arizona through early this
evening. Drier conditions will move in beginning Tuesday with rain
chances mostly ending through midweek. Expect MinRHs of 15-25% across the
western districts to 35-50% over the eastern districts today
before falling back to 15-25% areawide by Wednesday. Temperatures
will range from around normal over western districts to slightly
below normal over the eastern districts.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

SHORT TERM...Lojero
LONG TERM...Kuhlman
AVIATION...RW
FIRE WEATHER...Kuhlman/Lojero

NWS Phoenix (PSR) Office