814
FXUS65 KPSR 211145
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
445 AM MST Mon Sep 21 2026

.UPDATE...Updated 12Z Aviation Discussion.

&&

.KEY MESSAGES...

- Dry and tranquil conditions, along with near to slightly above
  normal temperatures, will continue for most of the region
  through at least the middle portion of the week.

- Low pressure and associated moisture will reintroduce rain
  chances for portions of Arizona over the next few days, but any
  rainfall activity for our forecast area will be focused
  primarily over foothill and high terrain areas through
  Wednesday.

- Isolated lower desert rainfall chances get introduced to the
  forecast during the latter portion of the week.

&&

.SHORT TERM /Today through Wednesday/...
Current objective analysis reveals shortwave troughing over the
Northern Plains, while a more potent upper-level low spins over
California. The latter of these systems will be the main weather
regime over the Desert Southwest during the front half of this week
as it pushed intermediate low-amplitude ridging further eastward.
However, the expectation is that the Pacific wave will weaken as it
moves further inland, so no significant day-to-day conditions
changes are in the forecast as dry and tranquil conditions will
continue for the vast majority of the region. Even with modest
height falls, temperatures will continue to run near to slightly
above normal for this time of year, which translates to lower
elevation highs hovering between 93-102 degrees.

The one exception to the dry and tranquil statement above during the
front half of the week will be portions of Northern and Eastern
Arizona thanks to increased moisture advection from the previously-
mentioned Pacific low. Not only will decent moisture be in place
over these areas with PWATs approaching 150-200% of normal, upper-
level ascent from anti-cyclonic flow and an upper-level jet streak
will provide and added layer of support for the development of
shower and thunderstorm activity. With that being said, coverage
over our forecast area will be minimal at best as atmospheric
thermodynamic profiles will not be quite enough to provide lower
desert rainfall. Rather, most, if not all, potential rainfall within
our forecast boundaries will be confined to higher terrain areas.

&&

.LONG TERM /Thursday through Sunday/...
By the latter half of the work week, the influence of the weakening
southwestern low will all but disappear. The focus will then shift
toward the interplay between large scale troughing over the eastern
Pacific/West Coast, and the sub-tropical high over the Southern
Plains and Northern Mexico. Global ensembles favor the retrograding
back toward the Desert Southwest as we approach the weekend, likely
staving off any advance, at least temporarily, of more anti-cyclonic
waves. This progression 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, thankfully,
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 1145Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation concerns are expected through the TAF period.
Winds will tend to follow their typical diurnal tendencies, but
with a slow turn to westerly by late this afternoon/early this
evening. So an extended period of southerly (crosswinds for KPHX
and KDVT) are expected this afternoon. Some occasional gusts into
the mid to upper teens are also possible this afternoon. Extended
period of light and variable winds are also anticipated, mainly
around the diurnal transitions, and especially overnight. SCT-
BKN mid and high clouds will continue through the period.


Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather impacts are anticipated through the next 24
hrs. Current light and variable winds at KIPL will go westerly
around 22Z with speeds generally aob 10 kt. However, a brief
period of occasional gusts up around 20 kt are possible this
evening (sundowner winds), therefor a TEMPO group has been
introduced for these gusts with this TAF package. Current light
and variable winds at KBLH will go southerly late this morning
and then southwesterly this evening. Winds will generally be aob
10 kt with some occasional gusts in the mid to upper teens
possible this afternoon. A TEMPO has also been added with this TAF
package for these wind gusts. SCT-BKN mid and high clouds will
gradually clear through the day with mostly clear skies expected
by this evening.

&&

.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...RW
LONG TERM...RW
AVIATION...Berislavich
FIRE WEATHER...RW