191
FXUS65 KPSR 081007
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
307 AM MST Sat Aug 8 2026

.KEY MESSAGES...

- Extreme Heat Warnings remain in effect through the weekend as afternoon
  highs will hover several degrees above normal while humidity
  values remain higher than normal, resulting in areas of Major
  HeatRisk.

- Shower and thunderstorm activity throughout the weekend will remain
  confined to the higher terrain areas with gusty outflow winds
  and areas of blowing dust the most likely impacts for the lower
  deserts.

- Deeper moisture will increase the chances for more widespread shower
  and thunderstorm activity heading into early next week along
  with cooling temperatures.

&&

.SHORT TERM /Today through Sunday/...
Latest objective analysis early this morning indicates the
subtropical high centered over Utah with 500 mb heights ranging
between 596-598dm across the region. These upper-level heights are
above the 99th percentile for this time of the year, indicating a
very warm airmass is in place throughout most of the atmospheric
column. As a result, afternoon high temperatures today will
generally range between 110-115 degrees across most of the lower
desert communities, which is a good 4-8 degrees above normal. The
subtropical high will weaken slightly on Sunday, resulting in
slightly cooler afternoon highs but still exceeding 110 degrees
across most of the lower desert communities. Given the afternoon
highs exceeding 110 degrees along with early morning lows
bottoming out in the middle 80s to lower 90s, high-end moderate
to areas of Major HeatRisk can be expected throughout the weekend
and thus the Extreme Heat Warnings remain in effect across all of
the lower deserts through Sunday evening.

The strong subtropical high sitting just to the north will continue
to result in strong subsidence and thus a good deal of convective
inhibition across the lower deserts today as well as into Sunday. As
a result, similar to the last several days, thunderstorm activity is
expected to develop across the higher terrain areas to the north and
east of Phoenix as well as across southeast AZ during the afternoon
hours, and migrate westward but likely weakening as the activity
approaches the lower deserts during the early evening hours. This
scenario is indicated by most of the hi-res guidance. However,
outflow winds from these storm complexes that do develop will
more likely affect the lower deserts with some gusty winds and
perhaps areas of blowing dust if the outflows that materialize
move through the dust prone areas. It will have to take a strong
outflow or collision of multiple outflows to overcome the
convective inhibition and result in the development of activity
in the lower deserts. Although this scenario is of low
probability, it cannot be totally ruled out.

&&

.LONG TERM /Monday through Friday/...
The overall pattern heading into the first half of next week is
likely to become more favorable for more widespread convective
activity across the region, including for the lower deserts. The
subtropical high is projected to weaken even further and migrate
more towards the Four Corners Region, resulting in the overall
flow to shift more out of the southeast. This will cause moisture
values to increase with the latest EPS and GEFS indicating PWATs
settling around 1.5-1.8" and low-level mixing ratios exceeding
11-12 g/kg. This increase in moisture will result in better
instability and weaker convective inhibition, making the
environment more favorable for storms that do develop across the
typical higher terrain areas to survive into the lower deserts.
This more favorable environmental setup is depicted in the latest
forecast from the NBM, which shows PoPs above 40% across the
south-central AZ lower deserts starting on Monday with elevated
chances continuing through the middle of the week. Which day early
next week could be the most active is difficult to pinpoint at
this time as it will be dictated by mesoscale processes that are
difficult to predict this far out.

Heading towards the latter half of the week, latest guidance
indicates the subtropical high migrating further eastward towards
Texas while an upper-level low sets up off the California coast.
This overall setup is likely to shift the flow more out of the
southwest, bringing in some drier air as PWATs drop under 1.5".
As a result, an overall downtrend in storm activity is likely by
the end of the week.

With the weakening of the subtropical high and in increase in
convective activity and cloud cover, temperatures next week are
expected to gradually cool with afternoon highs expected to fall to
near seasonal levels by Tuesday with afternoon highs of 102-108
degrees across the lower deserts. The NBM is even showing
temperatures potentially cooling even further through the end of the
week as it shows afternoon highs of 100-106 degrees, which if it
materializes, would be slightly below normal for the middle of
August.

&&

.AVIATION...Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main aviation concern will continue to be gusty outflow winds
during the afternoon and evening hours. Current TAFs reflect a
"best guess" given current guidance, but a number of adjustments
are certainly likely in subsequent forecasts given the very low
confidence of timing, strength, and orientation of potential
boundaries. It is not out of the question that no outflow moves
through metro terminals at all given the expectation that
convective activity across Arizona will be more muted compared to
days prior. In the meantime however, winds are expected to follow
diurnal trends into the afternoon hours, though the switch to the
west may take longer than usual as several hours of southerly flow
is being suggested. Outside of brief window of mostly clear skies
late this morning, SCT to BKN cloud decks will be common over the
region during the forecast window.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns are expected during the next 24 hours.
Familiar diurnal trends will prevail at each terminal, with SE`rly
winds switch out of the W at KIPL, and S/SW`rly flow being common
at KBLH. There is a low end chance (~10%) of an outflow from
distant convection moving through KBLH later in the period, but
confidence is too low to warrant mention in the TAF at this time.
FEW high clouds will be present through much of the forecast
window before mid-level decks move in early tonight.

&&

.FIRE WEATHER...
Above normal temperatures will prevail throughout the weekend
before gradually cooling to more seasonal levels by early next
week. Afternoon MinRHs will bottom out between 15-25% today and
increase slightly on Sunday closer to 20-25% areawide. Increasing
moisture next week will lead to MinRH values bottoming out above
20% along with good overnight recoveries. Shower and thunderstorm
activity will be mainly confined to the higher terrain areas to
the north and east of Phoenix as well as southeastern Arizona
throughout the weekend with more widespread activity, including
the lower deserts, more likely by early next week. Outside of
thunderstorm outflows, winds will follow the familiar diurnal
trends, with typical afternoon upslope breeziness around 20 mph.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530>544-546-
     548>551-553>555-559.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ560>570.

&&

$$

SHORT TERM...Lojero
LONG TERM...Lojero
AVIATION...RW
FIRE WEATHER...Lojero