759
FXUS65 KPSR 132355
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
455 PM MST Thu Aug 13 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- Isolated showers and thunderstorms will remain possible mainly
during the afternoon hours today and Friday with the best chances
across the Lower Colorado River Valley.

- Near to below normal temperatures are forecast through Friday
before heating back up over the weekend into early next week.

- An Extreme Heat Watch has been issued for Maricopa and Pinal
counties for next Monday through Wednesday.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
The upper level pattern remains mostly unchanged from this morning
with the upper level low over California, and the subtropical far to
the east in eastern Texas. With the low over CA southwesterly flow
has taken hold over the region with decent moisture being advected
into the Lower Colorado River Valley from tropical storms in the
Pacific. Current meso analysis shows PWATs near 1.5-1.6" along the
Lower Colorado, this moisture in conjunction with extra upper level
lift from the low to the west will lead to lingering chances (15-
20%) for isolated storms to develop later this evening. This is
supported within hi-res CAMs, highlighting storms developing along
the Lower Colorado River Valley into Southern Mohave County. For the
rest of the lower deserts chances for showers tonight are far more
limited, with a 10-15% chance of isolated showers possible, mostly
focused in the eastern portions of south central AZ and the higher
terrain areas. By Friday Shower and thunderstorm activity will
decrease further, as drier air will begin to scour out the current
moisture in the atmosphere.

Even though shower and thunderstorm activity will be decreasing
through today and Friday, the good news will be that afternoon high
temperatures will remain 4F-6F below normal through the rest of the
work week, thanks to the low remaining stationary over CA. This
translates to highs across the lower deserts between 96-103, and
widespread Minor HeatRisk. Morning lows will also be quite pleasant
Friday morning, ranging in the upper 70s to lower 80s.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
The weather pattern will shift over the weekend into early next week
as the subtropical ridge once again becomes the dominant weather
feature across the Southwestern U.S. The Pacific trough will
somewhat stick around into Saturday, but it is shown to quickly lift
to the north by Sunday as the ridge moves back in from the east.
Forecast H5 heights rise from 588-590dm on Friday to 591-594dm
Saturday before peaking around 594-596dm during the first half of
next week.

The dry air and increasing subsidence this weekend should keep all
but a few eastern Arizona high terrain showers and storms from
developing. Temperatures will warm up quickly over the weekend with
the expansion of the ridge with NBM forecast highs reaching 103-106
degrees Saturday and 106-109 degrees Sunday. The drop in moisture
will at least push surface dew points well into the 50s this weekend
to as low as the upper 40s early next week. This will help to keep
overnight lows close to normals through the weekend before we heat
up further next week. Ensembles eventually show the ridge center
shifting directly over Arizona by around Monday, likely staying in
place for a few days. The increased subsidence from the ridge with
no meaningful moisture return happening early next week should keep
lower desert PoPs below 10% to at most 10-20% over the far eastern
Arizona high terrain.

As the modestly strong (90-97th percentile of climatology) ridge
settles over Arizona during the first half of next week,
temperatures are likely to heat up enough to result in Major
HeatRisk across portions of the lower deserts. The highest
likelihood for Major HeatRisk looks to impact the Phoenix metro with
daytime highs around 110 degrees and lows around 90 degrees starting
Monday, but the more rural lower desert areas should experience
similar daytime highs as well. Due to the expectation of Major
HeatRisk, we have issued an Extreme Heat Watch for Maricopa County,
to include the Phoenix Metro, and Pinal County, valid from Monday
through Wednesday

&&

.AVIATION...Updated at 2355Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Uncertainty regarding TSRA/SHRA and wind shifts advancing into the
KPHX airspace this evening are the primary forecast challenges this
TAF cycle. Model trends suggest TSRA/SHRA remaining just south of
terminals this evening, and Prob30/VCTS mentions were adjusted to
only include KPHX with 10-20% chances for direct impacts elsewhere.
There is the potential for a gusty southerly outflow boundary
pushing north to affect operations early/mid evening. Otherwise,
occasionally thick mid/high clouds will be common with winds under
12kt outside of thunderstorm outflows.


Southeast California/Southwest Arizona including KIPL and KBLH:
Frequently thick mid/high clouds will be common through Friday
afternoon with only isolated TSRA/SHRA across the region this
evening. Chances for direct impacts on terminals appear to low for
mention in this TAF cycle, though a 10% chance still exists.
Otherwise, winds around 10kt with occasional gusts will oscillate
between SW and SE.

&&

.FIRE WEATHER...
Elevated humidity levels, below normal temperatures, and lingering
chances for showers and a few thunderstorms are expected today
before much drier air filters into the region Friday into the
weekend. Afternoon MinRHs of 30-50% today will drop to 20-30% by
Saturday and into the teens across the lower deserts starting
Sunday. Overnight recoveries will remain good to excellent. Winds
will remain predominately out of the south southwest much of the
period with overnight light easterly downsloping winds over the
eastern districts. Temperatures will warm back to normal by Saturday
and then above normal starting Sunday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Watch from Monday morning through Wednesday evening
     for AZZ534-537>544-546-548>551-553>555-559.

CA...None.

&&

$$

SHORT TERM...Ryan
LONG TERM...Ryan/Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman