431
FXUS65 KPSR 182320
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
420 PM MST Sun Oct 18 2026

.UPDATE...00Z Aviation Discussion

&&

.KEY MESSAGES...

- Chances for light rain will persist over Arizona higher terrain
locations east of Phoenix the next couple days with minimal
accumulation.

- Temperatures will gradually warm closer to the seasonal normal
through the middle of the week before abruptly cooling later this
week.

- A Pacific low pressure system moving into the Southwest later
this week will result in much better rainfall chances with the
possibility of a few embedded thunderstorms.

&&

.SHORT TERM /Today through Tuesday/...
Early afternoon WV imagery and objective analysis depicts an upper
level trough becoming elongated across the SW Conus with one
vorticity center ejecting through the four corners, while a
secondary circulation slowly moves into SW Arizona. A plume of
higher, anomalous PWATs around 1" continues to hover over southern
Arizona within the southwest flow on the leading edge of the trough
axis, though the majority of this moisture was relegated to the H7
layer and above. Ascent will continue to be maximized ahead of the
SW Arizona vorticity center through this evening, with some measure
of subsidence and drier midtropospheric air moving into the CWA in
its wake. However, enough moisture will remain in the midlevels
coincident with favorable cyclonic flow, sheared vorticity, and
another subtropical jet streak to support bands of light showers
through Monday afternoon. Orographic areas will be primarily favored
for accumulating light rain, but even a few isolated showers could
affect lower desert locations in south-central Arizona. With the
trough finally absorbed into the mean flow by Tuesday, precipitation
chances dwindle while modest height/thermal increases briefly spread
into the forecast area. As a result, forecast confidence is
excellent that temperatures will rebound near, or even a couple
degrees above the daily normals.

&&

.LONG TERM /Wednesday through Saturday/...
By Wednesday, deep troughing and strong negative height anomalies
will be established off the central/southern California coast, and
poised to move inland the remainder of the week. Ensemble and
deterministic modeling have come into much better agreement over
the past 24 hours with EPS members largely abandoning the idea of
a deeper, slower troughing driving eastward through the CWA.
Instead, the preponderance of ensemble output now support previous
GEFS solutions showing shortwave energy and the main cold core
lifting from southern California into southern Utah in response
to anomalous high amplitude, strong ridging stationed over the
central/southern plains. However, ECMWF forecasts continue to
highlight more robust moisture advection via deep, meridional flow
ahead of the trough passage into Arizona, though differences
among ensemble members are now becoming much smaller.

Regardless, Wednesday and Thursday continue to have the best window
for rainfall potential with the synoptic pattern strongly favoring
persistent moist upslope and orographically focused moderate
rainfall north and east of Phoenix. Occasional bands of showers will
undoubtedly extend into lower desert communities of south-central
Arizona with much of SE California/SW Arizona remaining dry. The
adjusted northerly track lifting away from the CWA also decreases
the potential for strong thunderstorm development, though a few
embedded storms would still be likely before rapid drying behind a
frontal passage sweeps through the region Friday. With better
ensemble agreement, the full suite of the NBM temperature spread
has narrowed slightly during this time frame with the expectation
of additional forecast confidence in future iterations showing a
rapid descent towards readings around 10F below normal by the end
of the week.

&&

.AVIATION...Updated at 2320Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation concerns are expected during the TAF period.
There will be a break from persistent E`rly flow this evening as
diurnal trends try to gain the advantage once again, but a
familiar full W`rly shift is not likely to emerge. Winds will once
again contain an E`rly component overnight, but speeds should be
noticeably lower than the past few days. There is a signal that
isolated SHRA may move within the vicinity of the terminals
tonight into Monday morning, but chances of that occurring
currently stand at 10% or less as most rainfall should remain over
the eastern portion of the airspace. After some brief clearing,
SCT low and mid-level cloud decks will be common with the lowest
bases around 6-8 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected over the next 24 hours under
mostly clear skies. Outside of some light W`rly and and
oscillations between NE and NW at KIPL and KBLH respectively,
winds will be generally light and variable.

&&

.FIRE WEATHER...
Wind speeds over the next few days will be much weaker than this
past weekend with minimal gustiness, however speeds and gust
frequency will increase again towards the middle of the week ahead
of an incoming weather disturbance. Occasional light showers may
continue to impact eastern districts, though wetting rainfall
potential is under 20%. Much better rainfall chances will arrive
during the middle of the week with amounts greater than 0.50" likely
east of Phoenix. Minimum humidity levels in a 30-50% range will be
common throughout the week with even higher readings likely across
eastern districts. Overnight recovery should be good to excellent
resulting in little to no fire weather concerns for at least the
next week.

&&

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

$$

SHORT TERM...18
LONG TERM...18/Ryan
AVIATION...RW
FIRE WEATHER...18

NWS Phoenix (PSR) Office