Phoenix, Arizona Weather Forecast Discussion

680
FXUS65 KPSR 241144
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
444 AM MST Wed Sep 24 2025
.UPDATE...Updated Aviation Discussion.
&&
.KEY MESSAGES...
- Hot temperatures for this time of year will affect the area
  through Thursday with lower desert highs near 105 degrees.
- Shower and thunderstorm chances will increase starting Thursday,
  first affecting areas mainly east of Phoenix.
- Widespread showers and thunderstorms are expected on Friday
  across south-central and eastern Arizona. Some strong to severe
  storms are likely along with localized heavy rainfall and the
  potential for flooding.
&&
.SHORT TERM /TODAY THROUGH THURSDAY/...
The main forecast concern continues to be the potential impacts
for later this week as a cut-off low moves into the region from
the west. However, in the near term rather hot and quiet
conditions are expected for today and a good portion of Thursday.
The cut-off low is currently positioned just west of L.A. with
upper level ridging positioned over Arizona into the Great Basin.
Today will bring drying conditions, especially across Arizona
where surface dew points are forecast to drop below 50 degrees
this afternoon. The drier boundary layer and near climatological
record 500mb heights overhead will help to heat things up today
with lower desert highs likely reaching 105 degrees across
portions of the lower deserts. As a result, the bulk of the area
will be covered by a Moderate HeatRisk with some localized Major
HeatRisk likely seen over south-central Arizona.
Going into Thursday, models remain in very good agreement showing
the cut-off low drifting eastward reaching south-central
California later in the day. As it gets closer to our region, it
will shift the winds in the lower levels out of the southeast
quickly advecting moisture northward into southeast and south-
central Arizona. The upper level ridge will still be in place
during this time with high temperatures essentially mirroring
today`s readings across Arizona.
The moisture advection on Thursday should be enough to boost
surface dew points well into the 50s again by the afternoon while
PWATs improve to around 1.2-1.3" over south-central Arizona. A
strong upper level jet will also move into southern portions of
our region on Thursday beginning to put much of eastern Arizona
into a favorable left exit region of the jet. Hi-res guidance
shows showers and thunderstorms developing by the afternoon from
southeast Arizona northward to the Mogollon Rim likely lasting
well into the evening hours. The steady stream of low level
moisture advection across this area and the increasing forcing
aloft very well could lead to a persistent area of showers and
thunderstorms prompting worries of heavy rainfall and potential
flooding. A Flood Watch will likely be needed for later Thursday
into Friday for at least the eastern Arizona high terrain.
A lower confidence forecast is seen for the south-central Arizona
lower deserts later Thursday into Thursday night. Hi-res guidance
generally shows the convection staying east of the Phoenix area,
but with high potential for outflow winds making their way into
the lower deserts. The outflow winds would at least bring a
blowing dust threat by Thursday evening into Pinal and eastern
Maricopa counties. We also can`t rule out the possibility of
showers and thunderstorms forming along the advancing outflow
potentially affecting the Phoenix metro. Convection is also very
possible during the overnight hours Thursday night anywhere from
Phoenix and areas to the east and southeast of Phoenix.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
Friday still holds fairly high potential for thunderstorm impacts
across south-central and eastern Arizona. Models are in very good
agreement showing the low moving southeastward into southeast
California during the daytime Friday. Even though this low is not
expected to be as strong as other transition type systems that
have brought severe weather outbreaks for our region, it still
could end up being quite the impactful weather system. As the low
enters our region on Friday, south southeasterly low and mid
level flow will increase further. We are likely to see a narrow
corridor of high instability building across our area by Friday
morning with MUCAPEs of 1500-2000 J/kg. The ingredients are likely
to be there for a line or a cluster of strong to severe storms to
develop somewhere across Maricopa, Pinal, and Gila Counties during
the first part of the afternoon as upper level forcing becomes
maximized. Forecast 0-6km bulk shear looks to be the strongest
during the morning hours Friday before gradually weakening during
the afternoon. It`s not impossible for some strong to severe
storms to develop during the morning hours, but it is more likely
to occur during the afternoon hours Friday. Strong to severe wind
gusts, moderately large hail, and heavy rainfall will all be
possible on Friday.
Moisture levels on Friday are not expected to be excessively high
with PWATs as high as 1.1-1.3" in a narrow corridor, but low
level mixing ratios will be quite good at 10-11 g/kg. The heavy
rainfall and flood threat will mostly come from persistent showers
and thunderstorms training over the same area over a period of
several hours. Average forecast rainfall amounts from late
Thursday through Friday are currently between 0.25-0.75" over the
Phoenix area to 1-2" across the high terrain east of Phoenix. At
this point in time, it seems quite plausible a few locations will
see localized higher rainfall amounts of 2-3". However, any
drastic change in the cut-off low`s strength and eventual track
may cut back on our forecast rainfall amounts.
Higher uncertainty is seen for Friday night and Saturday as the
cut-off low will likely begin to weaken and the position of the
low center is a bit uncertain. We are likely to still see decent
(30-40%) rain chances across a good portion of the area during
this time, potentially extending through southwest Arizona into
southeast California as the flow should temporarily shift out of
the east advecting better moisture westward. We are likely to lose
a good amount of our upper level jet forcing by Friday night, but
some residual forcing may still be in place across eastern
Arizona. Overall, any additional rainfall amounts beginning Friday
night should be on the lighter side with the flood threat likely
ending. We may even see rain chances extend into Sunday depending
on how long it takes for the low to eventually exit the region to
the north.
Temperatures will take a dive starting Friday with daytime highs
at most in the low to mid 90s. Some lower desert locations across
south-central Arizona may even fail to reach 90 degrees on Friday
depending on how early the convection starts. The lower heights
from the cut-off low will persist through the weekend with highs
likely only topping out in the upper 80s to around 90 degrees on
Saturday and Sunday, or 5-8 degrees below normal. Beyond Sunday,
forecast uncertainty remains somewhat high as a large Pacific
trough is likely to gradually shift southward along the northern
part of the West Coast. This should help to initially raise
heights over our region early next week, but it may eventually get
close enough to lower heights again. For now the NBM temperature
forecast shows highs remaining below normal through at least
Monday before inching back to near normal during the middle part
of next week.
&&
.AVIATION...Updated at 1145Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through the TAF period under
mostly clear skies. Winds will generally favor an easterly
component, though periods of variability or nearly calm winds will
be common for the next few hours and once again this afternoon.
Expect a surge of E/NE winds shortly after sunrise, with speeds to
around 5-10 kts and low to moderate confidence in some gusts up to
15-20 kts for a few hours. Confidence is moderate in a briefer
than usual wind shift to W/NW late this afternoon into the
evening, though speeds will be light (AOB 6 kts).
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are anticipated through the next 24
hours under clear skies. Very light winds (AOB 6 kts) will prevail
at both terminals with prolonged periods of VRB, except starting
around 01-03Z this evening at KIPL, winds will increase and shift
W/NW. This evening at KIPL, anticipate W/NW winds to around 10
kts with the potential for gusts up to 15-20 kts.
&&
.FIRE WEATHER...
Hot and dry conditions will continue today with moisture and rain
chances beginning to increase on Thursday. Expect isolated to
scattered thunderstorms over the eastern districts by Thursday
evening with chances increasing into Friday. MinRH values will
hover around 20% today before increasing Thursday into Friday with
values upwards of 50% over the eastern districts on Friday. Winds
will follow familiar diurnal trends today and most of Thursday
with some breeziness likely on Thursday. The slow-moving low
pressure system impacting the region late this week should lead to
widespread wetting rains across the eastern districts on Friday
and possibly Saturday. Below normal temperatures and elevated
humidities are expected for Friday and through the weekend.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Whittock
FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion