492
FXUS65 KPSR 271116
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
Issued by National Weather Service Tucson AZ
416 AM MST Sun Sep 27 2026

.KEY MESSAGES...

- A band of light rain will impact portions of the region later
  today and into Monday before more scattered showers and
  thunderstorms become possible starting Monday afternoon.

- A Flood Watch has been issued for Monday night and much of
  Tuesday for higher terrain areas of central and eastern Arizona.
  Moderate to heavy rainfall may also impact portions of the
  Arizona lower deserts, but we are expecting it to be much more
  localized.

- Near to below normal temperatures are expected through the
  middle part of the week before warming to slightly above normal
  by next weekend.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
The main forecast concern continues to be the potential for
widespread rainfall, particularly from late Monday through Tuesday
afternoon. Unfortunately, model guidance is still showing a good
deal of uncertainty with the timing and track of the incoming
Pacific low and how it will interact with the influx of moisture
through Monday. Current satellite imagery shows high level clouds
streaming into our region from the fast decaying TC Odalys well to
our southwest, while a much better organized TC Polo is slowly
drifting northward toward southern Baja. Even the forecast for
later today is a bit tricky as the higher level moisture from
Odalys will begin to interact with the incoming Pacific trough
which is approaching northern California.

We anticipate a continuous feed of higher level moisture from the
southwest for the rest of today and likely lasting into early
Monday morning. As this occurs, the moisture will gradually shift
more into the mid-levels due to top-down saturating of the layers.
There is also model evidence of some weak to moderate ascent
within the saturated layer prompting showers to begin to develop
later this morning. CAMs generally agree on increasing light
shower coverage later this morning, but most of this will not
reach the surface as the sub-cloud layer is starting out very dry.
This band of showers should eventually moisten the lower levels
enough by later this afternoon into this evening to allow for some
off and on light rain somewhere from southeast California through
southwest Arizona into around the Phoenix area. This rain is not
likely to amount to much, but most locations within this swath
should at least measure a few hundredths to maybe a tenth of an
inch. Some guidance shows a very narrow (25-50 miles maybe) of
amounts upward of a quarter inch from this evening through
tonight, which seems reasonable if it stays over the same area for
6-12 hours. We also can`t rule amounts upwards of 0.50" closer to
the mountains in northwest Maricopa County. The atmosphere should
remain quite stable through Monday morning, so we are at most
expecting a few rumbles of thunder.

Model trends over the past 24 hours has shown a little faster
progression of the Pacific low as it moves through our region
later Monday through Tuesday, as well as slightly less available
moisture. This still does not mean heavy rainfall will not happen,
it just means it will most likely be more confined to higher
terrain areas north and east of Phoenix and a more localized. The
center of the low is forecast to move into southern California by
Monday evening with increasing forced ascent during the latter
half of Monday and continuing through the first half of Tuesday.
The strongest forcing is expected just out ahead of the low
center, focused over the western deserts Monday afternoon/evening
and then progressing through southern and central Arizona Monday
night through Tuesday afternoon.

After the initial swath of light rain tapers off at some time
Monday afternoon, we are expecting scattered showers and
thunderstorms to develop somewhere along the Lower CO River Valley
late afternoon before slowly tracking eastward through southwest
Arizona in the evening/early overnight hours. A few of these
storms may end up being strong with potential for an isolated
severe storm too. Additional scattered showers with embedded
weaker storms are likely to impact higher terrain areas in Arizona
later on Monday before becoming more widespread at some point
Monday night and/or Tuesday morning. The timing is still a bit
uncertain, but the peak time frame for rainfall for central and
eastern Arizona looks to be between 3 AM Tuesday through Tuesday
afternoon. A Flood Watch has been issued for the foothills areas
of northern Maricopa County, northern and eastern portions of the
Phoenix metro and for the higher terrain northeast and east of
Phoenix. The Watch will be in effect from midnight Monday night
through the first part of Tuesday evening. Guidance generally
agrees the low will begin to exit the area to the east Tuesday
night with any shower activity winding down from west to east
during the evening/early overnight hours.

QPF amounts have gone down some from previous forecasts with
rainfall amounts averaging from around 0.1" in the Lower CO River
Valley to 0.35-0.75" for the lower deserts of south-central
Arizona. Higher amounts are expected within the Watch area,
averaging between 1.0-1.25", but localized amounts of 2-3" will
be possible. Keep in mind, there is still a good amount of spread
among the models for anticipated rainfall amounts and these
average expected amounts could still easily go up or down some.

As far as the strong to severe storm threat, the faster timing of
the system is leading to less of a severe storm threat. Forecast
instability remains the main issue with CAPE not likely getting
much above 500 J/kg. However, even with roughly 500 or maybe 750
J/kg, this may be enough to allow for a few stronger and maybe
even an isolated severe storm on Tuesday as the low center moves
eastward through central Arizona. As of right now, this limited
risk of severe storms is likely to stay across far southern into
southeast Arizona from late Tuesday morning through Tuesday
afternoon.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Upper level ridging is forecast to quickly surge in from the west
on Wednesday leaving clearing skies and lowering surface moisture
through Thursday. Temperatures for the coming week will stay
somewhat stable across the western lower deserts, but still on
average slightly below normal today through Tuesday. Much cooler
temperatures are expected for most of Arizona with highs only in
the 80s for the Phoenix area Monday-Wednesday. Once the ridging
moves in from the west later this week, temperatures will creep
upward again with highs topping 100 degrees across the western
deserts by Thursday or Friday and potentially for the Phoenix area
by next weekend.

&&

.AVIATION...Updated at 1000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

The primary aviation weather concerns during the TAF period will be
increasing chances for SHRA conditions and lower than usual
confidence on winds due to the potential showers and in the
vicinity. Winds will overall follow diurnal trends, however, current
guidance indicates a tendency for a more NW/N wind direction this
evening and through the overnight hours, and the typical
southeasterly nocturnal wind shift may not occur. Gusts into a 15-
25 kt range cannot be ruled out this evening as a result of nearby
shower activity. Better chances for SHRA arrive Monday morning,
leading to the introduction of the prevailing line at KPHX starting
around 12Z. Before Monday morning, rain will be fairly light and
isolated in coverage, with mostly virga showers initially. BKN-OVC
cloud decks with bases above 10K ft AGL will be common through
tonight, with FEW-SCT lower decks becoming introduced Monday
morning.

Southeast California/Southwest Arizona including KIPL and KBLH:

The possibility of VCSH/SHRA will be the main aviation concern in
the upcoming TAF period. Winds will fluctuate between SE and SW at
both terminals through the period, with speeds generally AOB 10 kts.
VCSH/SHRA will start to move into KIPL`s area later this
morning. Confidence in SHRA is low (less than 30%) so that has been
left out of the TAF for now. In fact, most rain may fall at virga.
At KBLH, any rain in the morning and afternoon is expected to remain
to the south and east of the terminal with better chances for
VCSH/SHRA at the terminal arriving after 00Z. BKN/OVC high clouds
will continue with FEW-SCT mid level clouds moving in later
this morning.

&&

.FIRE WEATHER...
Moisture will increase across the area today and Monday with
light rain developing this evening followed by locally moderate
to heavy rainfall with thunderstorm chances later Monday into
Tuesday. The bulk of the expected rainfall will favor the eastern
districts. MinRHs today will dip to 20-30% this afternoon before
improving to 40-60% over much of the area for Monday and Tuesday.
Winds through Monday will generally follow the typical diurnal
tendencies, but with a tendency to favor the south. A front moving
through the area on Tuesday will turn winds out of the west
northwest with gusty winds of 20-30 mph possible across the
western districts. Drier conditions and near to slightly above
normal temperatures are forecast for later this week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from late Monday night through Tuesday evening for
     AZZ534-537-541-542-545-547-549-552-555>558-560>563.

CA...None.

&&

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Whittock
FIRE WEATHER...Kuhlman