South West Weather

952
FXUS65 KPSR 132016
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
116 PM MST Sat Sep 13 2025

.KEY MESSAGES...

- Near to slightly below-average temperatures this weekend before
  gradually warming through early next week.

- No showers or storms expected this weekend through early next
  week, with mostly sunny skies and light winds.

- Potential for an increase in rain chances late next week with a
  push of moisture, but this forecast is still highly uncertain.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
Water vapor satellite imagery and the SPC mesoanalysis early this
afternoon show the base of the trough centered over central AZ,
with westerly flow aloft. This trough has brought in an abundance
of dry air, that can also be seen with water vapor satellite
imagery. The abundance of dry air is also present when looking at
the SPC mesoanalysis PWATs, which shows less than 0.8" PWATs over
our entire CWA and most of AZ. The only part of AZ that has PWATs
greater than 1" is in the far SE corner of the state. This is
where some storms have developed early this afternoon and is also
the only area where storms are expected in the state through the
evening. The aforementioned trough will continue to push eastward
through the weekend, which will also push the drier air further
east, allowing PWATs to fall below 1" state wide. As a result, dry
conditions are not only expected across our entire CWA, but the
whole state of AZ for tomorrow.

In addition to the dry conditions, the trough overhead is leading to
lower heights aloft which in turn results in cooler temperatures.
Temperatures (both low and high) are forecasted to be a few degrees
below normal through the weekend. Low temperatures this morning
were much more comfortable and pleasant and ranged from the mid
60s to mid 70s across the lower deserts and from the upper 50s to
low 60s across the higher terrain. Similar low temperatures are
forecasted tomorrow morning. Current temperatures early this
afternoon are also rather pleasant for this time of year and are
in the 90s across the lower deserts and 70s across the higher
terrain. High temperatures, this afternoon, are forecasted to top
out in the mid-to-upper 90s across the lower deserts and in the
80s across the higher terrain areas. As the trough pushes further
east tomorrow heights aloft will rise slightly, which will lead
to temperatures being a few degrees warmer tomorrow. Even with
temperatures in the 90s, it is still a good idea to practice smart
heat safety. Long exposure to 90 degree heat in full sun can have
negative effects without proper heat safety.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Heading into the beginning of next week, following the passage of
the trough this weekend, the synoptic pattern across the Desert
Southwest will enter a relatively weak westerly to southwesterly
flow regime, with high pressure ridging nudging back into the
area and H5 heights gradually rising. Global ensembles support H5
heights going from 582-582dam today to 588-590dam by Tuesday,
which is slightly above normal for this time of year. As a result,
this trend will allow temperatures to remain near seasonal levels
through at least Monday and then temperatures are forecast to
rise to or slightly above daily averages on Tuesday and Wednesday,
with lower desert highs forecast to reach the lower 100s.

This weaker flow pattern through early next week will allow for
at least a slow return of PBL moisture from the southeast, with
PWATs forecast to climb back to normal to slightly above normal
during the first half of next week. However, afternoon shower and
storm chances during the first half of next week will mostly
favor Southeast AZ, with NBM PoPs across South-Central AZ to
Southeast CA at or below 10% through Wednesday.

There still remains a high degree of variability in the forecast
for late next week, largely due to uncertainties in the magnitude
of moisture advection and potential showers and storms. There is
at least good confidence that tropical moisture will move up the
western coast of Mexico, along and west of Baja, with highest PWAT
anomalies favoring SoCal and just offshore by Thursday. While the
ensemble mean PWAT forecasts for the 3 primary global models are
pretty similar in magnitudes, each model still has large spreads,
with interquartile ranges up to 0.5 inches. The 25th percentiles
though, do have well above normal PWATs spreading across the
region, which is a good sign for shower and storm chances. There
is also the question of forcing for shower and storm development.
Given the overall weak synoptic pattern heading into late next
weak forcing may be very limited, unless shortwaves not yet
resolved in modeling can move through or troughing further up the
west coast can play a role. Latest NBM forecast has rain chances
going up starting Thursday in the western deserts and then
widespread 30% PoPs on Friday. Ultimately, it is still too early
to know what to expect. On the high end of the spectrum there
could be flooding rains while the other end may just be thick
clouds and little or no rain at all.

&&

.AVIATION...Updated at 1715Z.

South Central Arizona and Southeast CA including KPHX, KIWA,
KSDL, KDVT, KBLH and KIPL. No aviation concerns are expected
through Sunday morning under mostly clear skies. Winds will follow
familiar diurnal trends, with extended periods of variability,
especially for the western terminals. Speeds will remain generally
less 10 kts, with perhaps a few afternoon gusts in the mid-teens
for the Phoenix metro sites.

&&

.FIRE WEATHER...
Near to slightly below normal temperatures will be common across
the region through this weekend thanks to an area of low pressure
passing to the north. Outside of some breezy conditions this
afternoon in the eastern districts, with peak gusts up to 20-25
mph, winds will be light over the next several days and directions
will favor familiar diurnal trends. Dry conditions are expected
through the first half of next week with no chances for wetting
rains. MinRHs this weekend through early next week will mostly
range from 15-25% across all districts with fair overnight
recoveries at 30-50%. The forecast for the second half of next
week and into the weekend is still highly uncertain. However, a
push of moisture is expected to move into the region, which could
lead to better shower and storm chances.

&&

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

$$

SHORT TERM...Berislavich
LONG TERM...Benedict
AVIATION...RW/Frieders
FIRE WEATHER...Benedict/Berislavich