015
FXUS65 KPSR 151005
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
305 AM MST Tue Sep 15 2026

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

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

- The main forecast concern will be heavy rainfall and localized
  flash flooding from around the Phoenix metro into the higher
  terrain north and east of Phoenix.

- Shower and thunderstorm chances will greatly diminish by
  Thursday and generally come to an end starting Friday.

- Near normal temperatures through Thursday are expected to warm
  to slightly above normal by the weekend.

&&

.SHORT TERM /Today through Wednesday/...
Much of eastern and central Arizona will remain under the threat
of moderate to heavy rainfall through Wednesday with the best
chances likely late tonight through Wednesday afternoon or
evening. The main impetuses for this potential will be a Pacific
trough/upper level jet positioned just to our north and northwest,
a mid-level disturbance eventually moving through Arizona on
Wednesday, and a consistent plume of subtropical moisture
positioned over the eastern half of Arizona.

Current objective analysis shows a lull in activity as drier air
temporarily pushed eastward through all of southwest Arizona into
western portions of Maricopa County leading to PWATs as low as
1.4-1.6" in the Phoenix area. However, a strong Gulf surge is
starting to push its way northward into Yuma County and Pima
County with the expectation of this pushing surface dew points to
between 65-70 degrees and low level mixing ratios of 12-13 g/kg as
far west as the Lower CO River Valley. Broad upper level ascent
over the region will continue to improve today into tonight likely
peaking early Wednesday just as PWATs reach their max of 1.8-2.0"
across south-central Arizona. CAMs had been showing shower and
storm redevelopment somewhere near to northeast of Phoenix early
this morning, but satellite imagery is giving no signs of a
trigger for this to happen. The latest CAM runs have also backed
off or completely eliminated this convective potential. The most
likely scenario for today is for only isolated showers and maybe
a few storms through early afternoon before the convective
development gets going with the heating of the day, focused more
across the eastern Arizona high terrain. Forecast soundings do
show some support for a few strong storms this afternoon, but
given the somewhat moist lower levels, downdraft winds should stay
sub-severe. However, given forecast CAPE of up to around 1500
J/kg this afternoon, it would not be surprising to have one beefy
storm capable of producing severe wet microbursts. Chances remain
fairly good (40% chance) for some storms will develop as far west
as Phoenix or even just west of Phoenix later this afternoon
through this evening, but chances will be better after midnight.

Attention then turns to what should be the peak of this event as
PWATs increase and reach their peak late tonight through Wednesday
afternoon. Guidance shows rather good upper level ascent
developing over south-central Arizona after midnight and likely
persisting through much of Wednesday. We are also watching a mid-
level shortwave that is currently over the southern Baja area as
this is forecast to move into southern Arizona at some point from
mid morning to late afternoon Wednesday. The combination of the
upper level ascent and this mid-level disturbance is likely to
bring a period of widespread showers and isolated to scattered
thunderstorms. With PWATs anywhere from 1.6-2.0" and low level
mixing ratios of 12-14 g/kg late tonight through much of
Wednesday, it is likely some areas will receive moderate to heavy
rainfall at times. Both the GEFS and EPS mean QPF show average
amounts of 0.5-1.0" over the Phoenix area to 1.0-1.5" over much of
the higher terrain north and east of Phoenix. HREF guidance also
shows pockets of higher QPF amounts of up to around 2" possible.
The potential for moderate to heavy rainfall will be the highest
from just before sunrise to around sunset on Wednesday and this is
the likely time frame for a Flood Watch that will likely be
needed soon. We also can`t rule out a strong or severe storm
Wednesday afternoon due to improving winds aloft and bulk shear
increasing to 25-30kts, but given the likely extensive cloud
cover these chances remain fairly low. Although a low probability
of less than 10% or so, the best chances for a severe storm should
be over western Pinal and Maricopa County Wednesday afternoon.
Scattered showers and storms may persist into the overnight hours
Wednesday night, but the activity should be diminishing as upper
level ascent shifts more into New Mexico.

&&

.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 1005Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The potential for SHRA/TSRA and associated impacts will be the
primary weather concern through Wednesday morning under frequent
cloud decks 7K ft and above. Confidence is good that E/SE winds
will prevail through the morning. The majority of SHRA/TSRA this
morning is favored just east of the metro area. However, a few
SHRA/TSRA could redevelop near terminals prior to sunrise.

Forecast confidence deteriorates Tuesday afternoon and evening
contingent on activity in the morning. Moderate confidence exists
that winds remain E/SE or become southerly during the afternoon with
any additional TS holding off until the evening. Development and
coverage of storms Tuesday evening remains highly uncertain, however
somewhat better confidence exists regarding more widespread
SHRA/TSRA and significant operational impacts late Tuesday night
into Wednesday morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through Wednesday morning under
mostly clear skies. Winds will continue to behave similarly to the
past 24 hours with predominantly southeast at KIPL, and southerly
at KBLH with local afternoon gusts 20-25 kt.

&&

.FIRE WEATHER...
Periods of scattered showers and thunderstorms are expected
through Wednesday across the eastern districts supporting a
heavy rainfall and localized 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 Wednesday. 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 and lowering humidities into the teens
across the lower deserts.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...18/Benedict
FIRE WEATHER...Kuhlman

NWS Phoenix (PSR) Office