615
FXUS65 KPSR 220551
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1051 PM MST Mon Sep 21 2026

.UPDATE...Updated 06Z Aviation Discussion.

&&

.KEY MESSAGES...

- Dry and tranquil conditions, along with near normal
  temperatures will continue through at least the middle of the
  week.

- Rain chances will return to portions of Arizona over the next
  few days, although focused primarily over foothill and high
  terrain areas.

- Lower desert rainfall chances will be heightened somewhat
  during the latter half of the week.

&&

.SHORT TERM /Today through Wednesday/...
A seasonally strong trough was moving onshore in southern
California early this afternoon with a jet streak translating
downstream of the cold core forcing deamplification and lifting of
the cyclonic circulation towards the Great Basin. However, jet
forced ascent has combined with a narrow band of midlevel moisture
to produce a small area of elevated convection along the lower
Colorado River valley earlier today. This feature will continue to
exit the forecast area by this evening although residual,
elongated troughing will linger across southern California/Nevada.
This will create a deeply meridional flow pattern over the next
72 hours capable of importing sheared vorticity centers from the
south, as well as periodically better low level moisture profiles.
H5 heights will remain nearly steady state in a 580-584dm range
ensuring a continuation of near normal temperatures the next
several days.

Both global and HREF modeling suggests a low amplitude vorticity
center (likely convectively enhanced over northern Mexico)
streaming into eastern Arizona Tuesday afternoon. Along with a
small jet segment feeding into the right rear quadrant of the
northern stream, ascent structure tapping marginally better
moisture in SE Arizona will become very favorable for deep
convective development over higher terrain locations. While lower
elevations in the CWA will not initially have sufficient moisture
for thunderstorm sustenance, gusty southeast outflow winds seem
more likely, fostered by DCape values near 1500 J/kg allowing
better boundary layer moisture to surge northwest through the
forecast area. As a result, instability parameters will reach much
higher levels Wednesday (i.e. MLCape 1000- 1500 J/kg), though
stronger CinH and lack of a triggering mechanism may preclude more
than isolated mountain storms as the region may fall under
shortwave ridging and subsidence behind the Tuesday vorticity
center exiting the region.

&&

.LONG TERM /Thursday through Sunday/...
By the latter half of the week, the influence of the weakening
southwestern low will all but disappear. The focus will shift
toward the interplay between large scale troughing over the
eastern Pacific/West Coast and the subtropical high over the
Southern Plains and Northern Mexico. Global ensembles favor
retrogression toward the Desert Southwest approaching the weekend.
This evolution would not completely scour residual moisture
immediately, so rain chances will likely linger into Thursday.
Current PoPs show 30-50% chances for foothill and mountain areas
and 10-30% probabilities for the South- Central Arizona deserts.
Beyond that, persistent southwesterly flow would eventually dry us
out enough to limit rain chances heading into the weekend.
Another influx of moisture by the end of the seven day period may
bring rain chances back once again, but max chances at this time
only range between 20-30%.

Even with the competing airmasses, regional temperatures will
only fluctuate within a few degrees through the weekend. While the
ridge keeps another shortwave from progressing toward the region,
as mentioned previously, in return, the large scale troughing to
our west will keep the high from becoming too amplified,
preventing any further discussion of abnormal heat, at least
during this forecast period. Temperatures for the lower deserts
Thursday through Sunday will range generally between 94-106
degrees, while overnight lows hover near 70-82 degrees.

&&

.AVIATION...Updated at 0551Z.

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

Primary aviation impact will be the potential for VCSH/VCTS
Tuesday evening and gusty outflow winds. W`rly winds are expected
to continue for the next few hours, then shift back E`rly or
become VRB by 10-11Z. Winds will favor a S/SE direction through
the entire day with perhaps a brief period of W/SW winds in the
evening, but confidence in a W/SW shift is low. Wind speeds
will mostly stay below 10 kts. SHRA/TSRA activity is expected to
develop Tuesday afternoon and evening, but should mostly stay
south and east of the metro with a low chance (10%) to spread
into the metro. Outflow winds should move into the metro from the
S/SE with gusts up to 20-25 kts most likely and a low chance
(5-10%) for 30+ kts. FEW to SCT clouds will be common through the
TAF period with lowest bases around 8-10K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation impacts are anticipated through the next 24
hours with mostly clear skies. Winds will favor W/NW at both KIPL
and KBLH, with wind speeds mostly staying below 10 kts and periods
of light VRB.

&&

.FIRE WEATHER...
Near to slightly above normal temperatures will prevail over the
next several days, with minimal day-to-day fluctuations. Dry
conditions with no chances for rain continue through today ahead
returning high terrain rain chances for foothill and high terrain
areas starting Tuesday. MinRHs between 15-30% will be common across
the region, with even higher readings (35-50%) for the far eastern
districts. MaxRHs will range from fair to good over the western and
central districts, to good and excellent for the eastern districts
into the weekend. Outside of some marginal breeziness caused by an
approaching weather system, winds will follow familiar diurnal
trends with typical terrain induced afternoon gusts around 15-25
mph.

&&

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

$$

SHORT TERM...18
LONG TERM...RW
AVIATION...Benedict
FIRE WEATHER...RW