674
FXUS65 KPSR 122010
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
110 PM MST Sat Sep 12 2026

.KEY MESSAGES...

- Abundant moisture will remain situated across the eastern half of
Arizona providing enhanced chances for showers and thunderstorms
over mountain locations.

- Shower and thunderstorm chances will periodically extend into
lower desert communities of south-central Arizona.

- Near to slightly above normal temperatures are likely through next
week.

&&

.SHORT TERM /Today through Monday/...
Subtropical ridging has been dampened and displaced into northern
Mexico over the past 48 hours as enhanced westerly flow and
troughing in the northern jet stream descend into southern Utah.
Over the next 60 hours, the anti-cyclone center will become
reestablished over the SE Conus while quasi-stationary positively
tilted troughing settles over the Pacific NW and Great Basin. With
the ridge axis becoming oriented zonally across far southern
Arizona, weak S/SW flow will result over the forecast area yielding
periodic variations between modest subsidence and ascent. This flow
pattern will not be sufficient to scour away any moisture with
convectively favorable 12-13 g/kg low level mixing ratios being
maintained across the CWA.

Convective potential may be somewhat restricted this afternoon and
evening as synoptic scale subsidence spreads into the region behind a
shortwave shearing towards the four corners in the northern stream
westerly flow. However, given the ample boundary layer moisture,
isolated storms formed via moist, southwest flow over terrain
escarpments seems a reasonable outcome. While forecast CinH does not
appear overwhelming (less than 25 J/kg) and would seemingly support
additional storms along resulting outflows, HREF members advertise
minimal outflow boundaries and little to no additional
showers/storms. Regardless, a few evening thunderstorms and
lingering overnight elevated showers would not be out of the
question given the underlying moisture profiles.

While high resolution modeling indicates nearly identical convective
conditions Sunday with minimal impacts to lower elevations,
subsidence mechanisms appear largely absent while MLCape exceeds
1500 J/kg with almost no CinH. Admittedly, large scale ascent will
also be lacking, but any stronger outflow boundary, and/or colliding
boundaries would be supportive towards deep convective elements.
Thus, it wouldn`t be surprising if thunderstorm chances/coverage is
more expansive than the mandated NBM output or majority of HREF
forecasts during the late afternoon and evening. A similar argument
can be made regarding storm chances Monday where the NBM has been
loading higher POPs into the morning hours versus the more likely
evening time frame. While its conceivable elevated storms affect
parts of the CWA during the morning and a minority of modeling shows
light QPF in the 12-18Z time frame, this outcome is historically not
as common or likely; and the current forecast is initiated based on
frequently misleading NBM/WPC output with forecaster adjustments
made where human intervention is allowable. Of better confidence is
the temperature forecast over the next few days where readings
should fall within a few degrees of the daily normals.

&&

.LONG TERM /Tuesday through Friday/...
Rain chances will continue across the eastern half of Arizona during
the middle of the week as Pacific troughing lingers just to our
north and northwest, and ridging stays centered over the southeast
Conus. This will continue place Arizona in southwest flow providing
periods of moisture advection out of northern Mexico. The biggest
question that remains is what day, or days, will represent the best
chances for more than just scattered showers and isolated storms.
Models agree plentiful moisture will remain over eastern and central
Arizona through at least the middle of next week with PWATs running
150-180% of normal and low level mixing ratios anywhere from 11-14
g/kg. However, there are uncertainties with the amount of
instability due to forecast cloud cover and lack of any obvious
trigger mechanisms. Last night`s model runs were more optimistic
with upper level support, and this will likely be a piece of the
puzzle needed for an active weather day given the questionable
instability and inhibition.

The NBM is still honing in on early Tuesday as the best potential
for showers and thunderstorms across eastern and central Arizona,
but confidence in this is still fairly low. It would not be
surprising to have any day Tuesday through Thursday to be a good
storm day, but it is still too early to pinpoint which day or days.
With the upper level support leaning toward being less of an
influence, we may just have to rely on differential heating and/or
wherever the western edge of the moisture axis sets up. Forecast
instability does look to be enough to support some strong storms and
with the moisture levels expected, heavy rainfall leading to
localized flooding could also become an issue. Overall, rain chances
for next week look quite conditional and PoPs are likely to change.
Forecast temperatures for next week have also been trending upward
over the past few days with decreasing chances of having lower
desert highs dipping below 100 degrees on any day. The latest NBM
shows highs hovering right around normal to a few degrees above.

&&

.AVIATION...Updated at 1710Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns under FEW-SCT mid and high cloud
decks can be expected throughout the TAF period. The overall wind
pattern will generally favor diurnal tendencies with periods of
light variability likely at times, especially during diurnal
transitions. Overall wind speeds will generally be aob 10 kts.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns under FEW high cirrus cloud decks
can be expected throughout the TAF period. Winds will generally be
out of the southeast at KIPL and out of the south at KBLH. Winds
speeds will generally range between 8-14 kts with afternoon gusts in
the 20-25 kt range at KBLH.

&&

.FIRE WEATHER...
Slight chances for showers and thunderstorms can be expected through
the weekend with the best chances over the Arizona high terrain.
Chances are expected to increase across the eastern districts early
next week. MinRHs through early next week will generally be hover
close to 15-25% for the far western districts, while higher values
closer to 25-35% will be seen elsewhere. Winds will somewhat follow
typical diurnal patterns, but with more of a south southwesterly
predominant wind across the western districts. Daily afternoon gusts
of 20-25 mph will be common across the Lower CO River Valley this
weekend before becoming more widespread early next week.

&&

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

&&

$$

SHORT TERM...18
LONG TERM...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Kuhlman