880
FXUS65 KPSR 151952
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1252 PM MST Tue Sep 15 2026

.KEY MESSAGES...

- The combination of abundant moisture and a weather system moving into
  the region will help to bring several rounds of showers and
  thunderstorms across south-central and eastern Arizona through
  Wednesday.

- The main forecast concern will be heavy rainfall leading to
  flash flooding with flood watches in effect from late tonight
  through Wednesday evening across much of central and eastern
  Arizona.

- Shower and thunderstorm chances will greatly diminish by
  Thursday and generally come to an end starting Friday with the
  introduction of much drier air.

- Near normal temperatures, briefly dropping to below normal
  levels across south-central AZ on Wednesday, can be expected
  through the latter portion of the week before warming to
  slightly above normal levels by the weekend.

&&

.SHORT TERM /Today through Wednesday/...
A potentially very active period of weather is likely to
materialize, especially late tonight through the day on Wednesday,
across much of south-central AZ as several rounds of showers and
thunderstorms with moderate to heavy rainfall leading to flash
flooding are likely. Latest objective analysis shows the subtropical
high centered over the southeastern states with an upper-level
trough over the Pacific Northwest. This overall pattern
configuration is resulting south to south-southwest over Arizona
with more westerly flow from the lower Colorado River Valley
westward through southern California, helping to bring in drier air
across these areas. However, with the south to south-southwest
situated across much AZ, it is continuing to bring a constant plume
of subtropical moisture with PWATs across much of the south-central
AZ lower deserts above 1.5".

The combination of strong daytime heating and ample low-level
moisture will drive MLCAPE values of 1000-1500 J/KG this afternoon
with hi-res guidance indicating isolated to widely scattered storms
developing across the higher terrain areas of eastern and
southeastern AZ. Across the lower deserts of south-central AZ, there
is also the potential of a few storms very late this afternoon
through early this evening, especially across any terrain
escarpments given the near zero convective inhibition that is
forecast to be absent. Given the ample moisture in place, heavy
rainfall leading to localized flooding will be the primary threat.
However, strong downburst wind gusts will also be possible given
that DCAPE values are still projected to be sufficient high, near
1000 J/KG.

The main show is then forecast to materialize late tonight through
Wednesday as moisture increases further along with the forcing
for ascent. There will be a couple of features aloft that will
provide the forcing with a mid-level shortwave over the southern
Baja area expected to move overhead from the mid-morning to late
afternoon hours on Wednesday along with an upper-level jet streak
from the Pacific trough setting up along the Great Basin with the
region expected to be located along the right entrance region,
providing ample divergence aloft. The increased ascent combined
with the ample moisture will result in widespread showers and
thunderstorms, with the latest hi-res guidance indicating activity
starting near to just after midnight with several rounds of
activity into Wednesday evening. With projected PWATs expected to
peak between 1.8-2.0" along with low-level mixing ratios as high
as 14 g/kg and MUCAPE values in excess of 1000 J/KG, the overall
environment will be favorable for thunderstorms to produce heavy
rainfall rates in excess of 1-2"/hr and thus heighten the flash
flood potential. Both the GEFS and EPS mean QPF show average
amounts of 0.5-1.0" over the Phoenix area to over 1" over much of
the higher terrain north and east of Phoenix. However, locally
higher amounts are likely in the most persistent bands, with some
of the HREF members showing amounts in excess of 3-4". Therefore,
given the more widespread coverage along with the potentially very
heavy rainfall amounts for portions of the area, a Flood Watch
has been issued from late tonight through Wednesday evening for
all of the south-central AZ lower deserts and the higher terrain
areas east. Shower activity may persist across the region into the
overnight period, however, activity should be lighter in nature
given that most of the instability should be exhausted and the
overall coverage will be diminishing as the upper-level ascent
shifts away.

Afternoon high temperatures today will generally be right around
normal, with readings in the upper 90s to around 100 degrees across
the south-central AZ lower deserts to lower 100s across the western
deserts. With the abundant cloud cover and the rounds of rainfall
activity forecast, much cooler temperatures are anticipated for
Wednesday across south-central AZ with the potential that many areas
struggle to hit 90 degrees for afternoon highs. Across the western
deserts, afternoon temperatures with more sunshine should top out
the upper 90s to low 100s.

&&

.LONG TERM /Thursday through Monday/...
Drier air will gradually spread eastward on Thursday, with lower
desert rain chances mostly coming to an end. However, lower level
moisture will still remain in place likely allowing another round
of showers and isolated thunderstorms on Thursday across the
eastern Arizona high terrain. Given the drying aloft on Thursday,
the threat for heavy rainfall is expected to be much lower than
Wednesday. The synoptic flow is forecast to shift more out of the
west northwest late this week into the weekend and this will help
to bring a continuous flow of drier air through the region. By
Friday, PoPs are at most 10-15% in eastern Gila County to near 0%
in the Phoenix area. Lower level moisture should also eventually
get scoured out with surface dew points dropping into the mid 30s
to lower 40s across the western lower deserts to the upper
40s/lower 50s in the Phoenix area starting Saturday.

Temperatures will mostly be an afterthought for the next several
days with highs likely failing to reach 100 degrees in the
Phoenix area through Thursday to right around normal for the
western deserts. Once the drier air moves through the region later
this week, temperatures will begin to warm with lower desert highs
climbing up to around 105 degrees by Saturday.

&&

.AVIATION...Updated at 1818Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main impact through the TAF period will be SHRA/TSRA and
associated impacts. Chances are low this evening as models are not
in the best agreement at this time, so a PROB30 remains in the
TAFs at this time. Confidence is better compared to previous
packages for Wednesday morning, with models in good agreement that
VCSH will start just past midnight, then increasing coverage and
widespread TSRA impacts to the terminals by 11Z. The longevity of
significant operational impacts from TSRA activity may vary, with
periods of VCSH likely between redeveloping storms over the metro
heading into the afternoon and evening hours. During any TSRA
activity cloud bases between 5-6kft will be likely. Winds should
remain westerly through this evening switching out of the east for
the overnight hours with speeds mostly aob 10 kts. By Wednesday
morning winds will continue out of the east with speeds picking up
into the low teens with periods of gusts near 20kts.

Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through the TAF period under mostly
clear skies. KIPL will maintain a E-SE direction before eventually
going VRB Wednesday morning. KBLH will continue out of the south,
with gusts between 20-25 kts expected to continue through this
evening, then relaxing.

&&

.FIRE WEATHER...
Periods of scattered showers and thunderstorms are expected
through Wednesday across the eastern districts supporting a
heavy rainfall and flood threat. Moisture levels will remain
elevated except for southeast California. Expect minimum humidity
levels to still fall into a 15-25% range for the western districts
while the eastern districts will only dip to 35-50% through
Thursday. Winds will favor the south to southeast over much of the
area through Wednesday with gusts of 20-30 mph at times across
southwest Arizona. By Thursday into Friday, much drier air is
forecast to spread eastward across the region, eventually ending
rain chances for all but the far eastern Arizona high terrain
along with lowering humidities.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from midnight MST tonight through Wednesday evening
     for AZZ534-537>563.

CA...None.

&&

$$

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

NWS Phoenix (PSR) Office