770
FXUS65 KPSR 302335
AFDPSR

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

.UPDATE...00z 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/...
A hot and dry Labor Day weekend is in store as dry westerly flow
aloft persists over the region. The drier atmospheric conditions has
allowed for a lull in monsoonal activity along with plenty of
sunshine to help boost temperatures several degrees above normal.
Afternoon highs for this holiday weekend will warm up from around
103-108 degrees across the lower deserts today to around 105-110
degrees tomorrow. Given the warming temperatures for the weekend,
widespread Moderate to locally Major HeatRisk will expand across
the area. If you have outdoor plans this weekend, be sure to stay
cool and hydrated to avoid heat-related issues.

Dry conditions through the weekend will act to keep PWAT values
under an inch across our area and thus keep rain chances closer to
zero for much of the time. By Sunday afternoon, the center of the
subtropical ridge of high pressure will gradually shift northward
across Arizona and promote more moist easterly flow into eastern and
southeastern portions of the state. Chances for monsoonal showers
and thunderstorms will increase in these areas as a result with
slight chances (~20%) extending into portions of southern Gila
County.

&&

.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 2340Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are anticipated through the forecast period.
Winds will remain westerly with intermittent gusts into the teens
through sunset. Expect the typical diurnal easterly shift to
return late tonight by 06Z-07Z at KIWA and KPHX. Skies will remain
mostly clear aside from a few passing high clouds.

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 KIPL and
N-NW at KBLH through Sunday morning. Wind speeds should remain aob
6 kts, with periods of calm and vrb possible at both terminals.

&&

.FIRE WEATHER...
Mostly dry conditions continue through the weekend with near 0%
chance of wetting rains. MinRHs will mostly range between 10-20%
Sunday before climbing to around 15-25% Monday. 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...Smith
LONG TERM...Berislavich
AVIATION...Salerno
FIRE WEATHER...Smith/Berislavich