821
FXUS65 KPSR 022018
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
115 PM MST Tue Sep 2 2025

.KEY MESSAGES...

- Temperatures will gradually cool over the course over the next
several days with widespread below normal readings by the end of the
week

- Increasing moisture will promote daily shower and thunderstorm
chances for much of the region into the weekend

- Gusty winds, localized blowing dust, and isolated instances of
heavy rainfall will be common with any thunderstorms throughout the
week

&&

.SHORT TERM /Today through Wednesday/...
Expansive and high amplitude, but not particularly strong ridging
continues to remain parked over the western Conus with the H5 anti-
cyclone center migrating north into central Utah allowing more
pronounced E/SE flow to sweep into the CWA. A quasi-stationary
vorticity center has edged into northern Baja early this afternoon
with spokes of ascent rotating around the circulation center, and
responsible for the morning convection pivoting towards the
California coast. This synoptic pattern will remain quite favorable
for large scale ascent over the next 24 hours given broad jet level
divergence over much of Arizona juxtaposed with seasonally cooler
thermal profiles aloft and steeper midlevel lapse rates. Rich
moisture profiles exist across the western forecast area with a
plume of 11-13 g/kg mixing ratios surging north ahead of the
aforementioned vorticity center, while somewhat more marginal
moisture content (8-9 g/kg) exists in the eastern CWA with some
contribution of dry continental air in the heightened easterly flow.

Expansive cloud cover across SE California will likely hamper
instability while maintaining notable inhibition, and lesser
convective activity may also be common in the far eastern CWA with
less then optimal thermodynamic profiles. One area primed for deep
convective development will be along the international border, and
extending through western Pima, southern Maricopa, and Yuma counties
where 1000+J/kg MLCape will exist with minimal CinH. Storms have
already initiated on the eastern edge of the cloud shield and
associated with an outflow boundary in Yuma County, and HREF
membership is resolute in erupting strong storms over western Pima
County later this afternoon. Gusty outflow winds and areas of
blowing dust appear likely along the I-8 corridor in advance of the
storms with impacts transitioning towards localized flash flooding
this evening as activity congeals over SW Arizona.

Forecast confidence deteriorates rather substantially Wednesday with
todays convective outcome, an evolving synoptic pattern, and
developing tropical disturbance influence potential instability and
ascent structure. Outflows and moisture distribution from convective
complexes this evening should improve thermodynamic profiles across
the forecast area with forecast BUFR soundings suggesting deep sfc-
H7 mixing ratios 10+ g/kg. With less cloud cover, insolation should
allow ample instability with forecast soundings indicating a very
favorable, nearly uncapped thermodynamic profile reaching a typical
"sweet spot" of 1200 J/kg MLCape and DCape. However, HREF members
are not particularly enthusiastic about storm development within the
forecast area, but rather initiating activity across northern
Sonora/far southern Arizona. This may be the case where the CWA
aligns between more favorable lifting mechanisms of the vorticity
center lifting into southern NV and the approaching tropical
disturbance off the Baja coast. Depending on how the ascent
structure advances ahead of the tropical circulation near the Baja,
outflows from convective complexes could result in numerous
overnight showers/storms setting the stage for potentially more
storms Thursday.

&&

.LONG TERM /Thursday Through Monday/...
Southeasterly flow will remain in place heading into the latter
portion of the week keeping rain chances in the forecast through
Saturday for parts of the region, especially for those high terrain
areas of eastern AZ. For the Phoenix metro, the Thursday-Friday
timeframe looks to be the best for rainfall as a reinforcing push of
moisture enters the region making conditions more conducive for
widespread lower desert activity. However, there are some factors
that are making it difficult to pinpoint the exact day of activity.
Thursday activity maybe limited across parts of the state due to
cloud cover being sheared off from what could soon become Tropical
Storm Lorena. Friday may be the better day for activity due to
slightly better moisture availability and less cloud cover, a setup
more conducive for widespread convective activity. One thing that
appears more certain though is decreasing temperatures through the
week. Weakening high pressure along with increased moisture and
cloud cover will help bring temperatures to below normal levels by
the latter half of the week with some lower desert locations even
struggling to reach the triple digits by as early as Wednesday.

By the end of the weekend and the start of next week, signs point to
dry southwesterly flow making its return across the region likely
shutting down rain chances for a while. Drier conditions are likely
to result in a rebound in regional temperatures with most areas
outside of lower elevation communities seeing the return of triple
digits.

&&

.AVIATION...Updated at 1735Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty winds and potential for reduced visibilities will be the main
aviation concern this TAF period. Theses gusty winds will generally
be between 20-25 kts and will continue through the afternoon, but
look to subside by this evening. Convective activity will mainly be
focused to the south and west of the terminals this afternoon and
currently do not look to propagate into the Phoenix Metro area, but
could produce outflows from the SW that could result in a few hours
of blowing dust. Winds will have a late switch out of the west by 00-
01Z before weakening for the overnight period, where VRB conditions
will be common. SCT-BKN mid to high lvl clouds will prevail over the
region with bases aoa 10 kft.


Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation concerns this TAF period will be the potential for
VCSH/VCTS and gusty winds at both terminals. A line of storms have
developed generally west of the terminals, but redeveloping showers
and storms are anticipated over the next several hours, primarily at
KIPL but KBLH could be affected as well at this time. KIPL will keep
a NNW`rly component through the afternoon, followed by VRB
conditions for the overnight period. Another round of showers and
storms will be possible at KBLH late this afternoon with winds
predominately out of the W-NW. Cloud bases are expected to be aoa 10
kft, however could briefly lower to around 7-9 kft with any passing
shower/storm.

&&

.FIRE WEATHER...
Increasing moisture levels across the Desert Southwest will result
in a gradual enhancement of daily shower and thunderstorm chances
over the next several days. Due to this increased moisture flux,
MinRH values will remain around 15-25% through the middle of the
week, likely rising even higher later this week due an additional
moisture push and cooling temps. MaxRHs will follow a similar trend,
with good to excellent overnight recoveries expected into the
weekend. Near to slightly above normal temperatures will be common
across the region today before widespread below normal readings are
observed through the latter part of the week and into the weekend.

&&

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

&&

$$

SHORT TERM...18
LONG TERM...RW
AVIATION...Ryan
FIRE WEATHER...RW