570
FXUS65 KPSR 271201
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
501 AM MST Sat Sep 27 2025

.UPDATE...12Z Aviation Discussion.

&&

.KEY MESSAGES...

- Shower and thunderstorm chances will continue this weekend,
  particularly today across southwest Arizona and southeast
  California where a few strong storms and locally heavy rainfall
  may occur.

- A Flood Watch will be in effect from mid morning through the
  afternoon for portions of southeast California and Southwest
  Arizona.

- Below normal temperatures with lower deserts highs in the upper
  eighties to around ninety degrees this weekend will warm back
  to near normal by the middle of the upcoming work week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
The upper level cutoff low which set up South-Central AZ for
scattered instances of severe weather and fairly widespread flash
flood impacts yesterday is currently centered over Imperial
County, CA. At this hour, showers and a few thunderstorms feeding
off elevated instability are wrapping around the center of the
low, affecting only East Riverside County for the most part. With
the proximity of the low and associated forcing, coupled with
above median levels of moisture for the time of year (based on SPC
sounding climatology of PWATs for YUM and PHX) across the eastern
CWA and even higher values towards the west, expect continued
chances for showers and thunderstorms across most of the area
today. Much of the activity across South-Central AZ should remain
focused north and east of Phoenix, though a few showers in the
Metro area cannot be ruled out, and rainfall amounts will
generally remain under 1". The main focus for thunderstorms and
heavier rainfall totals today will be across Southwest AZ and
Southeast CA.

Better quality moisture continues to cyclonically wrap around the
core of the cutoff low, with RAP analyzed PWATs up to 1.2-1.3"
across Southwest AZ and East Riverside County, near to slightly
above the 90th percentile of climatology for the date (based on
YUM soundings). Late this morning, guidance shows modest
instability developing along this core of better moisture,
particularly just east of the Lower Colorado River, with HREF
mean MUCAPE values upwards of 500-750 J/kg and higher values
further south. Though these values represent fairly modest
instability, the excellent moisture profile out west and low CIN
environment near the low will allow for storms to realize almost
all of this instability. Thunderstorms developing within the Watch
area will be quite efficient rain producers, capable of dropping
upwards of 1.0-1.5" with the stronger cells. A few storms may be
capable of producing strong wind gusts and small hail. Across
Southwest AZ, storms may move quick enough that some amount of
training echoes will be required to produce localized instances
of flash flooding, as GFS deterministic 700-500 mb southerly
winds will be 10-15 kts. For Southeast CA, slow storm motion will
mean that individual storms may be capable of localized rainfall
amounts of 1+" and minor flood concerns. As such, the flood
threat today is lower than that of yesterday, but enough evidence
existed for a Flash Flood Watch to be issued for these areas out
west, in effect from 9 AM MST/PDT through the afternoon.

One complicating factor for the flood threat to be realized today
will be cloud cover, which would limit instability and prevent
stronger storms with better rain rates from developing. With this
in mind, the Flood Watch could be cancelled if conditions do not
evolve as anticipated.

Sunday, anticipate drying conditions and much of the area falling
under subsidence as the cutoff low continues to weaken and move
off to the northeast. Lingering rain chances will cling mostly to
the AZ high terrain during the day and fall below 10% statewide by
the evening.

&&

.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 1150Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary aviation weather concerns through Saturday evening
will be two main rounds of SHRA/VCTS. High-res guidance suggests
that there will be a round of SHRA developing this morning, mainly
after 15Z and quickly progressing nwd by this afternoon. Another
round of scattered showers and isolated storms will be possible
this evening around 01Z-02Z. Confidence in any direct impacts to
the terminals is low at this time. Winds will remain E-SE through
much of the day, but there will likely be a transition to westerly
flow later this evening due to outflow from storms west of the
metro. Cigs will range between 5-6 kft this morning before rising
to 8 kft through this afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
The main weather concerns through the forecast period will be
SHRA/TSRA arriving by this afternoon. Due to the presence of
convection in the area and an upper lvl low situated over SE
California, wind directions are expected to vary quite a bit.
However, the primary wind direction should be NE at KIPL and N at
KBLH this morning. Winds should return to the S-SW at KBLH by this
afternoon. By mid/late afternoon, scattered TSRA should begin to
erupt over SE California/SW Arizona though exact coverage and
timing are more uncertain. Probabilities are better at KBLH with
the chance for a prolonged period of TSRA. Gusty winds and lowered
visibilities would be common with any TSRA directly impacting an
aerodrome before activity wanes Saturday evening. Cigs could lower
to around 5 kft as storms progress through the region.

&&

.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 from 9 AM MST this morning through this afternoon
     for AZZ530>533-536.

CA...Flood Watch from 9 AM PDT this morning through this afternoon
     for CAZ560-561-564-565-568>570.

&&

$$

SHORT TERM...Whittock
LONG TERM...Whittock
AVIATION...Salerno/18
FIRE WEATHER...Whittock