Flash Flood Warning 79, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
449 PM MST Sat Sep 27 2025

.UPDATE...00Z Aviation Discussion.

&&

.KEY MESSAGES...

- Shower and thunderstorm activity will continue to affect
  portions of southwest Arizona and southeast California with more
  isolated activity across south-central Arizona through this
  evening.

- A drier and much quieter weather pattern will settle across the
  region beginning on Sunday.

- Below normal temperatures will prevail through the weekend
  before gradually warming up to near normal by the middle of next
  week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
The upper-level low pressure system that has been causing impactful
weather during the last couple of days remains situated near
southeast CA as of early this afternoon. Along the eastern flank of
the low, shower and thunderstorm activity have erupted across
portions of southeast CA and southwest AZ, with activity expected to
continue across these through this evening before eventually
dissipating completely. With MLCAPE values ranging between 500-1000
J/KG along with PWATs between 1.2-1.5", the environment will remain
favorable for some stronger storms capable of producing heavy
rainfall amounts in excess of 1-2" in a short amount of time. Thus,
the flash flood potential will remain elevated with a Flood Watch in
effect through early this evening. Farther east, across south-
central AZ, the shower and thunderstorm activity will remain more
isolated in coverage and thus not nearly as impactful as yesterday's
activity where widespread flash flooding was observed. Nevertheless,
any storms that do move across will be capable of producing brief
heavy downpours but the quick residence time should limit rainfall
amounts.

Heading into Sunday, the upper-level low will finally weaken and
move eastward through central AZ and thus most of the region will
remain on the subsident side. Therefore, thunderstorm activity will
be much more limited in coverage with chances mainly across the
AZ high terrain and any terrain escarpments through the afternoon
before rain chances end completely by the evening hours.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
By Sunday night into Monday, our region will transition more into
zonal flow to weak ridging as a deep Pacific low moves southward to
off the Pacific Northwest coast. Temperatures will remain 5-8
degrees below normal areawide this weekend with the help of the
cutoff low over SoCal. Once we start to see weak ridging back into
our region early next week, daily highs will gradually warm,
attaining near normal values for the time of year (middle 90s for
the lower deserts) during the middle of the upcoming work week.

&&

.AVIATION...Updated at 2349Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary aviation concern is the potential for further showers
and thunderstorms as activity continues to be spotty across the
metro. The bulk of the activity that is spread across the metro
currently looks to linger until ~01-03Z this evening, where winds
can be erratic in their direction. Exact location of storms is
uncertain at this time so only VCTS is reflected in the TAFs.
Outside of any convection, winds will favor an E'rly component
through much of the evening before a later than usual shift to the
W tonight once the aforementioned storms have cleared. Lowest
cloud bases will be around 5-6k ft, with CIGs in conjunction with
any rainfall down near 7-8k ft.

Southeast California/Southwest Arizona including KIPL and KBLH:
Main concern during the TAF period will be potential SHRA/TSRA
activity through this evening. Best timing for convection in the
vicinity looks to be between 00-04Z. Typical impacts can be
expected with gusty and erratic winds and reduced VIS at times.
Otherwise, winds at IPL will switch to the W for most the
overnight period around 03Z when storm activity is beginning to
clear the area. At KBLH a similar W'rly shift will occur once
storms have cleared but will settle back out of the SSE by
tomorrow morning. However, both terminals can expect periods of
VRB during the overnight period as well. Lowest cloud based are
expected around 6-7k ft during this evening's activity.

&&

.FIRE WEATHER...
As a low pressure system meanders over Southern California, chances
for wetting rainfall and isolated to scattered thunderstorms
remain today, mainly focused over the high terrain of the eastern
districts (20-50% CWR) and fairly widespread across the western
districts (30-60% CWR). Rain chances will end across the area by
Sunday evening, with only lingering chances over the AZ high
terrain Sunday during the day. MinRHs will continue in the 30-45%
range and temperatures in a 5-8 degrees below normal range
areawide today and Sunday, with humidity gradually decreasing and
temperatures gradually warming early next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch until 6 PM MST this evening for AZZ530>533-536.

CA...Flood Watch until 6 PM PDT this evening for CAZ560-561-564-565-
     568>570.

&&

SHORT TERM...Lojero
LONG TERM...Whittock
AVIATION...Ryan
FIRE WEATHER...Whittock

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