666
FXUS65 KPSR 132022
AFDPSR

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

.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 1735Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main aviation concern will be the potential for isolated
thunderstorms this afternoon into the early evening. Have upgraded
VCSH to VCTS in the valley TAFs as the risk for thunder is around
for a short time, generally just in the 22z-01z time frame.
Outside of local gusty winds near showers/storms, winds are
expected to follow normal diurnal trends. For cloud cover,
mid/high level clouds will be common.

Southeast California/Southwest Arizona including KIPL and KBLH:
The main concern is the risk for storms up the Co River valley and
into Blythe later this afternoon and into the early evening. VCTS
has been added at KBLH from 22z-01z for this increased chance.
Otherwise, aviation concerns will be minimal. Winds will
generally follow diurnal trends. Mid/High clouds will be common
through the period.

&&

.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...Frieders
FIRE WEATHER...Kuhlman