993
FXUS65 KPSR 301135
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
435 AM MST Sat Aug 30 2025

.UPDATE...Updated 12z Aviation Discussion.

&&

.KEY MESSAGES...

- Temperatures for the Labor Day weekend will rise slightly above
normal, leading to increasing widespread Moderate HeatRisk.

- Overall dry conditions will prevail through the weekend before
rain  chances gradually increase through the upcoming workweek.

&&

.SHORT TERM /Today through Sunday/...
Dry conditions and westerly flow is in place, as seen by the 500 mb
RAP analysis and water vapor satellite imagery, early this morning.
With high pressure overhead and mostly clear skies this weekend, we
will see temperatures warming to near normal today and above normal
tomorrow. Forecasted high temperatures are in the 102-108 degree
range across the lower deserts (and in the 96-103 degree range
across the higher terrain) today and in the 105-110 degree range
across the lower deserts (and in the 98-105 degree range across the
higher terrain) tomorrow. These increasing temperatures will lead to
widespread Moderate HeatRisk this holiday weekend. If you have
outdoor plans this weekend make sure to stay cool and hydrated.
Considering altering your plans to limit your time outdoors during
the heat of the day, especially those sensitive to the heat.

Overall dry conditions will continue through the weekend across the
CWA. High pressure will start to build over the region by Sunday
into Monday. This will result in a return of easterly flow and some
limited moisture, which will lead to a slight chance (10-20%) of
showers and thunderstorms across the southern Gila County high
terrain.

&&

.LONG TERM /Monday through Friday/...
As we turn our attention to next week the subtropical ridge will
strengthen over western CONUS through the first half of the week,
with the peak of the ridge actually stretching up to the US-Canada
boarder. Ensembles show the strength of the ridge being between 591-
594 dm during the first half of next week. This will lead to
temperatures remaining largely unchanged and slightly above normal
for the first half of the workweek. This will result in widespread
Moderate HeatRisk continuing across the lower deserts. So those
especially sensitive to the heat will need to take extra precautions
to protect themselves from heat related injuries. If you have
outdoor plans for Labor Day on Monday, you may also need to alter
you plans to minimize your time outdoors, especially during the
hottest times of the day.

With the ridge strengthening over the region, the overall synoptic
pattern will return to a more favorable pattern for monsoonal
activity as flow overhead becomes easterly across eastern AZ, and
southerly/southeasterly over SE CA and SW AZ. Daily thunderstorm
chances will continue across the AZ higher terrain (20-40%).
Thunderstorm chances will be increasing daily across the lower
deserts, however will generally say around 10-40% during the first
half of the workweek. In order to support better monsoonal activity
we will need better moisture across the region. Ensembles continue
to show PWATs dropping below an inch (in the 0.8-1.0" range) this
weekend. Ensembles also show PWATs slowly building back into the
region next week with the easterly/southerly flow across the region.
Ensembles show PWATs increasing to 1.1-1.4" across south-central AZ
and 1.3-1.6" across SE CA and SW AZ (the ECMWF ensemble is running
about 0.2" higher than the GEFS). The higher PWATS across western
portions of the CWA are because of the southerly/southeasterly flow,
which is more favorable for more moisture return. This increased
moisture out west shows up in the PoPs as PoPs are about 10% higher
across SE CA and SW AZ vs over the south-central AZ lower deserts.
The first half of the week may end up being more of outflow days for
the lower deserts of south-central AZ, including the Phoenix Metro,
which will also help to improve our moisture. Some showers and
storms could still pop-up, especially if we get multiple colliding
outflow boundaries.

As we head towards the end of the workweek, ensembles are in fairly
good agreement the ridge will weaken some as a trough moves into the
Pacific NW. Ensembles show H5 heights falling to around 588-590 dm.
As the high weakens it will also move slightly eastward, which will
allow for flow to become southeasterly across the region. This will
lead to increasing PWATs across the CWA. Ensembles currently show
PWATs maxing out during the Thursday-Friday timeframe around 1.4-
1.8" across the CWA (the ECMWF ensemble continues to be around
0.2" higher than the GEFS). Regardless the Thursday/Friday
timeframe currently looks to be the best day for monsoonal
activity. With the ridge weakening some and increased cloud cover
from any monsoonal activity, temperatures are also forecasted to
cool off some. Afternoon high temperatures are currently
forecasted to fall below normal and be in the mid to upper 90s
across the lower deserts (and in the upper 80s to low 90s in the
higher terrain) on Thursday and Friday. While models are in fairly
decent agreement regarding the overall pattern a lot can still
change, especially as each day`s activity will depend on how the
previous day plays out. However, if we get enough moisture to
move back into the region, it could shape up to be a pretty active
week.

&&

.AVIATION...Updated at 1130Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are anticipated through the forecast period.
Generally light and variable or easterly winds this morning will
return out of the WSW by 18Z-19Z through this evening. Skies
should remain mostly clear aside from a few passing high clouds
through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected through the forecast period
under mostly clear skies. Winds will be primarily W-NW at both
terminals into the morning hours, becoming more N-NE at KBLH
Saturday morning. Speeds should remain aob 5 kts, rendering
periods of light and variable conditions at both terminals
throughout the period under clear skies.

&&

.FIRE WEATHER...
Mostly dry conditions continue through the weekend with near 0%
chance of wetting rains. MinRHs will mostly range between 15-20%
this weekend. Winds will remain fairly light, with typical
afternoon breeziness, through the period while mostly following
typical diurnal trends. Temperatures this weekend will rise
slightly above normal with highs approaching 110 degrees for some
lower desert areas by Sunday. Chances for monsoonal activity will
gradually increase through next week, with activity starting as
early as Sunday across the higher terrain in eastern Arizona.

&&

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

$$

SHORT TERM...Berislavich
LONG TERM...Berislavich
AVIATION...Young/Salerno
FIRE WEATHER...Smith/Berislavich