Phoenix, Arizona Weather Forecast Discussion

711
FXUS65 KPSR 170523
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1023 PM MST Tue Sep 16 2025
.UPDATE...Updated 06Z Aviation Discussion.
&&
.KEY MESSAGES...
- Above normal temperatures with localized Moderate Heat Risk will
  continue through Wednesday across the lower deserts with highs
  peaking around 105 degrees this afternoon.
- Temperatures are will fall below normal by the latter half of
  the week before slowly rising over the weekend into early next
  week.
- Remnant moisture from TC Mario will result in increase rain
  chances over the next few days with the best chances focused
  across southeast California and southwest Arizona on Wednesday
  before expanding across the entire region Thursday and Friday.
- Lingering showers will be possible through this weekend, mainly
  over the high terrain features of southcentral AZ.
&&
.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Latest satellite wv imagery and 500 mb streamline analysis reveals
a very chaotic upper lvl pattern across the western U.S. There is
currently a broad ridge of high pressure situated over N MX while
a cutoff low is progressing through the Intermountain West.
Tropical Storm Mario is currently located about 300 miles off the
coast of the Baja California. The latest update from the NHC shows
this storm continuing to progress N-NW over the next 24-48 hrs
and dissipating due to interaction with cooler waters and increase
wind shear. The positioning of the ridge over N MX and a cutoff
low off the coast of CA will promote moisture advection through
interior MX into our forecast area and promote increasing rain
chances over the next few days.
Moisture advection is already ongoing across southwest AZ with
dewpoints in the mid 60s being reported in Yuma. This increased
moisture should help to spark off some very isolated showers and
thunderstorms this afternoon across southeast California and
southwest Arizona, focused mostly over prominent higher terrain
features. There will also be a secondary focus for storms this
afternoon in S Gila County around Globe/Miami. Elsewhere across
the lower deserts, expect partly cloudy skies with highs reaching
slightly above normal, around 100-105 degrees. Lows tonight will
settle back into the upper 70s to mid 80s.
High pressure will continue to weaken on Wednesday, resulting in
temperatures cooling by a few degrees region-wide, but still
remaining slightly above average in southcentral AZ. Ensemble
members continue to show PWAT values rising to around 1.5-2.0"
across southeast CA and southwest AZ and around 1.2-1.5" in
southcentral AZ on Wednesday which is around 150-200% of normal for
this time of year. This increase in boundary layer moisture will
result in an axis of higher ML CAPE up to 1000-1500 J/kg across
southwest AZ and southeast CA on Wednesday afternoon where scattered
showers and thunderstorms are progged to develop. A few storms could
be strong with gusty winds and blowing dust being the main threats.
Farther east into central AZ, increasing cloud cover will likely
limit instability initially, however a leading shortwave trough
moving nwd out of MX could help destabilize the boundary layer
and steepen lapse rates late Wednesday evening into Wednesday
night. Hi-res models indicate a batch of showers and storms
arriving into the forecast area during this timeframe. The latest
NBM PoPS reflects this with an increase to around 20-30% across
the lower deserts of southcentral AZ Wednesday night.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
As we stated yesterday, model uncertainty was still quite high for
later this week, so it`s not surprising the forecast has shifted
back to better rain chances for Thursday and Friday. Guidance
remains confident in good low and mid level moisture seeping into
the entire area by Thursday as the remnants of Mario inch toward
or reach the southern California coast. The remnants of Mario are
also likely to get incorporated into a larger scale trough off the
coast with a jet streak strengthening across our region Thursday
into Friday. Guidance is now showing even better upper level
forcing for Thursday and Friday, as well as at least some modest
upslope forcing into central Arizona. However, one negative factor
is guidance shows a good amount of dry air aloft surging into our
region from the southwest later on Thursday into Friday. This
drier air aloft should inhibit heavy rainfall to a degree.
The latest forecast calls for scattered showers and isolated
thunderstorms likely focused across southeast California during
the first part of Thursday before spreading into southern and
central Arizona by Thursday evening through the overnight hours
Thursday. NBM PoPs of 40-60% are seen across much of the area
Thursday and Thursday night. Rain chances for Friday are a bit
more uncertain, but with the drier air likely moving in from the
southwest chances are likely to be focused more across the Arizona
higher terrain. Forecast QPF amounts for the entire event show the
highest amounts of 0.5-0.75" across the western half of Maricopa
County through northern Yuma and much of La Paz Counties. Higher
elevations across southeast California could also see upwards of
0.5-0.75". Guidance also shows roughly a 5-15% probability of
seeing an inch or more of rainfall from this event with the
highest chances focused across western Arizona.
Temperatures later this week are certain to drop with the increase
in moisture, clouds, and decent rain chances. The latest NBM
guidance shows highs more on the lower end of guidance with
readings mostly in the mid 90s for Thursday and Friday. As ridging
gradually builds back over our region into the weekend and
conditions gradually dry out temperatures are sure to rebound.
Forecast highs are seen creeping back to around 100 degrees by
Sunday and potentially even toward 105 degrees by the middle of
next week.
&&
.AVIATION...Updated at 0523Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation concerns through the TAF period. Winds will
continue to favor typical diurnal patterns, shifting out of the
east around midnight tonight through the overnight period. Wind
speeds will generally aob 10kts. FEW- SCT cumulus clouds will
continue, and build throughout tomorrow to SCT-BKN by the
afternoon. Cloud bases will be aoa 10kft.
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds at both terminals are expecting more S`rly flow, teetering
between SSW and SSE through most of the overnight period before
W`rly flow is established tomorrow afternoon. Wind speeds are
expected to mostly be aob 10 kt, however outflows tomorrow
afternoon may produce occasional gusts between 20-25kts.
Additionally, there is a slight chance (~20%) for VCSH starting as
early as tomorrow morning, but mostly in the afternoon, primarily
at KIPL. FEW-BKN cumulus are expected through the day, with bases
around 10K ft AGL.
&&
.FIRE WEATHER...
Slightly above average temperatures will continue today and
Wednesday. Increasing moisture and cloud cover will resulting in
cooler temperatures for the latter half of this week. Isolated
showers and storms will be possible on Wednesday, with the best
chances for widespread wetting rains occurring Thursday and
Friday. MinRHs this afternoon will fall to around 20% before
steadily increasing to around 40% late this week. Outside of any
thunderstorms, will remain light over the next few days with
directions mostly following diurnal trends.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...Salerno
LONG TERM...Kuhlman
AVIATION...Ryan
FIRE WEATHER...Salerno

NWS PSR Office Area Forecast Discussion