861 
FXUS65 KPSR 201016
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
316 AM MST Sat Sep 20 2025

.KEY MESSAGES...

- Near to slightly above normal temperatures will be common 
  across the area through at least the middle of next week.

- Chances for showers and isolated thunderstorms will return on
  Sunday with the potential lasting through at least Monday.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
Upper level ridging and drier air has shifted over the region 
since yesterday providing mostly clear skies early this morning. 
An upper level trough remains situated off the West Coast with 
guidance showing this feature strengthening some over the next 
couple of days, while drifting more toward our region. However, 
the subtropical ridge will remain in charge for the rest of today 
with plenty of sunshine boosting daytime highs to around 100 
degrees this afternoon. 

As the trough to our west begins to shift toward the West Coast
later today into Sunday, it should become cut off from the main
flow and quickly pick up some moisture residing over Baja and 
western Mexico. A stream of mid-level moisture is forecast to 
reach southern California during the morning hours Sunday before 
spreading into Arizona in the afternoon and evening hours. This 
moisture should boost PWATs over much of our area to between 
1.3-1.6" on Sunday with the moisture layer stretching from around 
750-400mb. Over the past few days guidance has continued to trend 
wetter with this system, despite the lack of good instability. 
Modest mid and upper level forcing along with the moisture 
advection should be enough to get showers going mainly across 
southeast California starting Sunday morning before spreading into
central and potentially southern Arizona during the afternoon and
evening hours. This stream of good moisture is likely to persist 
through Sunday night providing even better chances for showers and
maybe a few isolated thunderstorms.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Monday morning is likely to be the peak of the rain chances with 
NBM PoPs of 30-40% fairly widespread across the area. These PoPs 
very well could be underdone as this may end up being a somewhat 
larger area of rainfall resulting in most locations receiving 
light amounts of a few hundredths of an inch to upwards of a 
0.25". Lower forecast confidence is seen through the rest of 
Monday into Tuesday as guidance tries to mostly end rain chances, 
but keeps the cut-off low just off the southern California coast. 
This position may still allow for chances for isolated showers and
thunderstorms, despite the NBM drastically lowering PoPs down to 
around 10%. Even if rain chances do continue into Tuesday, most 
locations may not see much if any rainfall as ensemble mean PWATs 
are forecast to lower to around 1.1-1.3" by later Tuesday. Given 
the higher than normal forecast uncertainty, don't be surprised if
the forecast shifts during this time.

Temperatures early this week are likely to start out near normal
with highs mostly in the upper 90s across the lower deserts, but
that may change going into the middle part of the week. Forecast 
temperature spread has improved enough to provide for fairly high
confidence in warmer temperatures by next Tuesday or Wednesday.
The latest NBM shows highs likely reaching 100 degrees by Tuesday
with some potential for Phoenix to reach 105 degrees on Wednesday. 

We are not likely to get rid of the cut-off low very quickly as
guidance shows the low first drifting a bit to the north across
southern/central California before potentially turning eastward 
at some point around next Thursday or Friday. It is unknown at 
this time if this shift will actually occur and how far it will 
venture to the east as the ensembles try to move it into western 
Arizona by next weekend. If the low does fully move into our 
region later next week it may bring a return of better rain 
chances and cooling temperatures, but that is a big if as cut-off 
lows are very hard for models to forecast. 

&&

.AVIATION...Updated at 0515Z. 

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are anticipated through the forecast period.
Winds will remain generally less than 7 kts and follow typical
diurnal patterns. Light easterly flow will prevail overnight and
gradually shift back to westerly at all terminals by 19Z-20Z
tomorrow. Skies will remain mostly clear with the exception of a 
FEW cumulus developing over the region tomorrow afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: 
No aviation weather concerns are anticipated at the SE California
terminals under mostly clear skies. Winds will remain predominantly
W at KIPL and NW at KBLH overnight before transitioning to NW at 
KIPL and S at KBLH by Saturday afternoon. Speeds should remain aob
7 kts through the period.

&&

.FIRE WEATHER...
Modest drying will occur today with better moisture returning to 
the region Sunday into Monday. Rain chances will also return on 
Sunday with the best chances likely Sunday night into early Monday
with wetting rain chances between 20-30%. Minimum humidity levels
will generally fall into a 25-30% range following good to 
excellent overnight recovery of 50-90%. Winds will remain rather 
light with limited upslope gusts. A slow moving weather system may
impact portions of the region during the rest of next week 
keeping humidities a bit elevated and potentially additional rain 
chances. 

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Salerno
FIRE WEATHER...Kuhlman