580
FXUS65 KPSR 160516
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1015 PM MST Tue Sep 15 2026

.UPDATE...
Updated Aviation

&&

.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 resulting in flood watches from late tonight through
Wednesday evening across much of central and eastern Arizona.

- Shower and thunderstorm chances will greatly diminish by Thursday,
coming 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 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 0515Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A low confidence forecast continues through Wednesday night with the
threat of a longer duration, high impact TS event at some point
Wednesday. Before that, confidence in wind trends overnight is only
moderate with a brief periods of light SW over parts of the airspace
before switching back to easterly. Trends in models suggests chances
for SHRA/TSRA pushed back later into the day Wednesday with lower
chances of morning impacts, and better chances during the mid/late
afternoon.

In addition to direct TSRA impacts at terminals within the PHX
airspace, instances of MVFR (and possible brief IFR) flight
categories are possible in the form of lowered vsby and cigs. A
period of strong outflow wind gusts and BLDU are also possible with
the initial surge of TS, though precise details on timing and
location preclude any mention in this TAF package. SHRA may linger
well into the early evening depending on evolution of the TS
complex, with a lower chance of additional TSRA. The most likely
outcome is for TS to exit the PHX area late afternoon leaving an
overturned atmosphere with expansive midlevel cigs and lack of
instability for further SHRA/TSRA development. Have maintained a
prob30 mention Wednesday evening with low confidence.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Wednesday night under
mostly clear skies. Confidence is good that KIPL winds will largely
maintain a SE direction, however periods of variability will be
likely during the morning hours. Winds at KBLH will continue with a
southerly component with afternoon gusts 20-25 kts. Confidence is
growing that a strong outflow boundary with gusty east winds will
surge westwards across the Colorado River late afternoon. The
current odds suggest SHRA/TSRA remaining well east of the terminal
location, however BLDU could move into the area with the gusty east
winds.

&&

.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...18
FIRE WEATHER...Kuhlman/Lojero