698
FXUS65 KPSR 080529
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1029 PM MST Sun Sep 7 2025
.UPDATE...06Z Aviation Discussion.
&&
.KEY MESSAGES...
- Drying conditions over the next several days will end rain
chances across the forecast area by Monday.
- Temperatures warm back into the normal range today through
around Tuesday then cool below normal during the latter half of
the week.
- Localized Moderate Heat Risk is expected mainly across the
south-central Arizona lower deserts during the first half of
this week with highs as warm as 105 degrees.
&&
.SHORT TERM /Today through Tuesday/...
Ridging aloft continues to build in response to a longwave trough
off the West Coast. RAP analyzed H5 heights have already
increased to 592 dam over the forecast area, and ensembles
advertise H5 heights hovering around 592-594 dam through Monday.
As a result, anticipate warming temperatures into the early part
of the upcoming workweek, with NBM highs in the upper 90s to lower
100s this afternoon warming another few degrees by Monday to
100-105F across the lower deserts. Meanwhile, very dry air aloft
evident in midlevel wv imagery will begin to mix down into the
boundary layer this afternoon, though residual low level moisture
(widespread GFS and RAP analyzed near-surface mixing ratios in
excess of 12 g/kg) will support another round of isolated showers
and weak storms this afternoon over prominent terrain features of
Southwest and South-Central AZ. This includes the Kofa Mtns,
Harcuvar Mtns, Table Top Wilderness, and Pinal Mtns to name a few
of the most likely areas for development - in fact, shortly after
noon local time, weak showers had already initiated in each of
these areas except Table Top. Cumulus had begun to develop over
these peaks within a few hours after sunrise.
Drying conditions within the boundary layer are much more evident
in guidance Monday onward, with dewpoints likely to drop below
60F for much of the lower deserts and mixing ratios gradually
decreasing to below 10 g/kg, drying from west to east. Coverage
of showers will become even more isolated over higher terrain
areas Monday and essentially nonexistent across the forecast area
Tuesday in response to this drying trend. The drying trend can be
attributed to the sustained west/southwest flow aloft, which will
be enhanced as the longwave trough off the West Coast moves
onshore Tuesday. Another impact of this trough moving onshore
will be cooling temps during the middle of the week, most
noticeably across the Western Deserts on Tuesday, and the onset
of fairly widespread breezy conditions.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
The Pacific trough will become the main driver of our weather
starting Wednesday as the low center moves into northern
California and the base of the trough moves over central and
southern California. This should push daytime highs well into the
90s across southeast California, but highs across south-central
Arizona are still likely to top 100 degrees on Wednesday. Breezy
conditions areawide are also expected Wednesday (and possibly
Thursday) with afternoon gusts to around 25 mph. Guidance is also
indicating some very modest moisture across eastern Arizona for
Wednesday and Thursday, but it is expected to be quite shallow and
should at most bring 10-20% PoP chances across the high terrain.
Ensembles are now in better agreement showing the Pacific trough
stalling out over the Western U.S. as it continues to weaken
before finally lifting the northeast next weekend. The lower
heights from the trough should keep highs in the 90s across most
of the lower deserts late this week to as high as around 100
degrees in the Phoenix area. Overnight lows should also continue
to improve later this week with lows dipping into the 60s across
the western deserts to the low to mid 70s in the Phoenix area.
Eventually by late next weekend and into the following week,
heights are favored to trend upward again after we lose influence
from the trough. This should lead to some slight warming and
highs back to just over 100 degrees.
&&
.AVIATION...Updated at 2325Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns are anticipated through the forecast
period. Winds will follow typical diurnal patterns, becoming
easterly at KIWA overnight and a for a few hours around sunrise at
KPHX before returning to the WSW late Monday morning. Skies will
remain mostly clear with the exception of a FEW CU with bases
around 7-8 kft developing again Monday afternoon.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are expected over the next 24 hours
under mostly clear skies. Winds will remain predominantly westerly
at KIPL and southerly at KBLH with speeds aob 10 kts through the
forecast period.
&&
.FIRE WEATHER...
Drying conditions and near normal temperatures are expected over
the next several days as high pressure influences our region. Over
prominent terrain features of Southwest and South-Central AZ, CWR
is at most around 10% in some isolated spots this afternoon, and
some showers and weak thunderstorms have already developed. By
Monday, CWR drops to near zero areawide. MinRHs today will stay
elevated at 25-35% before gradually lowering to between 15-25% by
Tuesday. Winds will continue to be light and favor diurnal
patterns through Monday before a uptick in winds is likely during
the middle part of the week. By Wednesday into Thursday, an
incoming low pressure system mainly to our northwest may allow for
some isolated shower and thunderstorm chances largely over the
eastern Arizona high terrain. Temperatures will also cool back to
slightly below normal later this week with humidities staying
stable through Thursday before drying out even more Friday into
next weekend.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
SHORT TERM...Whittock
LONG TERM...Kuhlman
AVIATION...Salerno
FIRE WEATHER...Whittock/Kuhlman
NWS Phoenix Office
Tucson, AZ 
