844
FXUS65 KPSR 090612
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1112 PM MST Sat Aug 8 2026

.UPDATE...Updated 06Z Aviation Discussion.

&&

.KEY MESSAGES...

- Extreme Heat Warnings remain in effect through Sunday evening
  with highs and lows several degrees above normal and higher
  than normal humidity, resulting in areas of Major HeatRisk.

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

- Deeper moisture will provide a better opportunity for more
  widespread shower and thunderstorm activity by early next week,
  including in the lower deserts, along with cooler temperatures.

&&

.SHORT TERM /Today through Sunday/...
Current GOES mid-lvl wv imagery and 500 mb streamline analysis
reveals an unseasonably strong subtropical high centered near the
4-Corners region with height fields approaching 596-598 dam.
Heights of this magnitude are above the 98th percentile of
climatology for early August. Due to the overall strength of this
ridge, and responding low-lvl thermal provide, temperatures will
once again top out well above normal (5-8 degrees) this afternoon.
Most lower desert communities will see highs in the 110-115
degree range, resulting in a widespread Major HeatRisk. The
Extreme Heat Warning remains in effect today across the lower
deserts of AZ and southeast CA, thus it is important to continue
practicing smart heat safety. The center of the subtropical high
will begin to slowly shift ewd on Sunday which will allow 500 mb
height fields to lower ever so slightly across the Desert
Southwest. This will cause temperatures to tick down a couple of
degrees, but still remaining in a well above normal range Sunday
afternoon with lower desert highs reaching 108-112 degrees. Given
the afternoon highs exceeding 110 degrees along with early morning
lows bottoming out in the middle 80s to lower 90s, the Extreme
Heat Warnings will remain in effect across all of the lower
deserts through Sunday evening.

Similar to the last several days, thunderstorm activity is
expected to develop across the higher terrain areas to the north
and east of Phoenix this afternoon and migrate westward but likely
weakening as the activity approaches the lower deserts during the
early evening hours. Forecast soundings for the lower deserts
indicate a strong inversion in the 700-600 mb layer. Latest RAP
analysis also shows MLCIN values approaching -90 to -110 J/kg
across Maricopa County which will likely limit storm activity
across the lower deserts. What is more likely will be an outflow
boundary associated with a decaying complex of storms over the
foothills NE of Phoenix which could bring strong, gusty winds into
portions of Maricopa County. Winds could gust between 25-35 mph
for a couple hours as the outflow sweeps through. Patchy blowing
dust will also be possible, especially for areas south and west of
the Phoenix Metro. Very similar conditions are anticipated on
Sunday in terms of areal coverage of thunderstorms with NBM PoPs
ranging from 10-25% across the lower deserts of southcentral AZ.
Again the main impacts from any storms will be gusty outflow winds
in excess of 30 mph.

&&

.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 0612Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Strong outflow winds, blowing dust, and VCTS/TS at the terminals
will be the primary forecast challenge and potential impact for
Sunday. There is good confidence that one or multiple outflow
boundaries will move through the terminals Sunday evening, with
wind gusts up to 20-30 kts anticipated and around 50% chance for
peak gusts >30 kts. The outflow winds will be capable of bringing
a wall of dust through the metro. There will also be slight
chances (20%) for VCTS/TS. Timing of activity Sunday is favored
between 02-05Z.

Preceding Sunday evening, there is a lot of uncertainty in wind
directions, especially through the morning. Confidence on whether
winds will turn E at KPHX is low. FEW to SCT clouds will be
common through the period, with lowest bases staying at or above
10K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH:
An outflow boundary looks poised to move through KBLH from the E
around midnight tonight, which may bring a brief period of
easterly wind gusts up to 20-25 kts and some lofted dust.
Potential for VCSH/VCTS with this boundary is low. Through the
rest of the TAF period there are no major aviation weather
concerns expected. Both terminals will mostly favor a SW-SE wind
direction with light winds in the morning and overnight hours and
8-12 kts with gusts to 20-25 kts in the afternoon and evening at
KBLH. FEW to SCT mid and high clouds will be present through much
of tonight and Sunday morning.

&&

.FIRE WEATHER...
Above normal temperatures will prevail through this 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. Low-level moisture
will continue to rise through early next which will promote much
better overnight recovery. Shower and thunderstorms 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 arriving by
early next week. Chances of wetting rainfall will also increase
significantly early next week. Outside of gusty and erratic winds
due to thunderstorms, 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...Salerno
LONG TERM...Lojero
AVIATION...Benedict
FIRE WEATHER...Lojero/Salerno