317
FXUS65 KPSR 121706
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1005 AM MST Tue Aug 12 2025

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- Areas of major HeatRisk with Extreme Heat Warnings in effect
through Wednesday for portions of the central AZ lower deserts, the
Lower Colorado River Valley, and Imperial Valley.

- Increasing moisture later this week will result in better coverage
of thunderstorm activity across much of the region including the
Arizona lower deserts.

- Temperatures will gradually lower later this week likely reaching
into the normal range by Friday.

&&

.SHORT TERM /Today through Wednesday/...
Northerly dry flow aloft across the bulk of Arizona remains in
place, but some boundary layer moisture is still there due to
nightly weak Gulf moisture surges. PWATs across the area have
dropped to between 0.9-1.1" which for this time of year is quite
dry. The main forecast concern in the short term continues to be the
hot conditions and areas of Major HeatRisk. The subtropical ridge
has briefly made a bit of a comeback to our northwest leading to
slightly higher heights over the Desert Southwest. Daytime highs
yesterday reached as high as 115 degrees across southeast California
and between 109-112 degrees in the Phoenix area. Highs today are
likely to be on par with yesterday`s, keeping the Extreme Heat
conditions in place over much of the lower deserts. The limited
moisture should continue to only allow for some isolated convection
over the eastern Arizona high terrain with PoPs up to 20%.

For tonight into Wednesday, the center of the ridge will shift
eastward reaching near the Four Corners area by Wednesday afternoon.
This shift in the high is expected to turn the winds more out of the
northeast into southern and central Arizona while also advecting in
some slightly better moisture from New Mexico. PWATs by Wednesday
afternoon are forecast to rise closer to 1.1-1.3", but low level
mixing ratios are still expected to fairly low at between 7-9 g/kg.
NBM PoPs for Wednesday are still looking too generous, but chances
will be higher than today with 10-15% chances into eastern portions
of the south-central Arizona lower deserts to 30-40% over the
eastern Arizona high terrain. The chances for gusty outflow winds
will also increase into the lower deserts by Wednesday evening.

The Extreme Heat Warning has been extended through Wednesday evening
as NBM guidance has trended warmer for Wednesday with highs only a
degree cooler than today. Overnight lows Tuesday night/Wednesday
morning will also remain quite warm with lows between 85-90 degrees
within the warned areas.

&&

.LONG TERM /Thursday through Monday/...
The forecast for later this week is still fairly uncertain as the
subtropical ridge center shifts farther to the east into the
Southern Plains while a weak trough moves onshore into California.
The main uncertainty is with how much moisture will advect into
southern and central Arizona between Wednesday and Friday. Both the
GFS and Euro show a period of southerly moist flow into Arizona from
Wednesday night through Thursday night with PWATs rising to 1.3-1.6"
centered over south-central Arizona for Thursday night into Friday.
The positioning of the trough to the northwest should also provide
for a day or two of modest upper level support over the region. This
scenario does provide for the potential for an active monsoon day,
but some negatives are seen, such as a weak southwesterly steering
flow and lower desert convective inhibition.

Shower and thunderstorm chances are expected to increase on Thursday
before peaking on Friday as moisture levels reach their peak. NBM
PoPs still look too high for both days considering the set up, so we
have adjusted lower to 20-30% and 30-40% chances for south-central
Arizona for Thursday and Friday. Both days should present at least a
40-50% chance across the eastern Arizona high terrain. Some very
marginal moisture may seep into southeast California and southwest
Arizona leaving a 10-15% chance of some isolated showers or storms
focused more over any higher terrain features. Both days could
result in a storm or two that may end up being strong or marginally
severe, but overall guidance doesn`t indicate this will support any
organized strong to severe storms. Moisture levels should also be
too low to support a decent heavy rainfall or flood threat, but due
to the weak steering flow we may end up seeing a few storms getting
anchored to higher terrain features that could produce localized
heavy rainfall.

Eventually guidance shows the trough shifting more into our region
later Friday into Saturday pushing drier air in from the west
southwest. This should reduce the rain potential considerably by
Saturday and even more so on Sunday as PoPs lower to only a 10-20%
chance over the eastern Arizona high terrain.

Temperatures will also cool off across the region late this week,
partially due to the falling heights with the introduction of the
trough and also due to the increased moisture and convection. The
biggest drop should happen between Thursday and Friday as NBM
guidance shows highs dropping to between 102-107 degrees across the
lower deserts. Near normal temperatures should hold into Saturday
before beginning to warm again Sunday into early next week.

&&

.AVIATION...Updated at 1705Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Uncertainty regarding outflow winds and periods of reduced slantwise
visibilities will be the primary weather issues through Wednesday
afternoon under a few mid/high cloud decks. Confidence is very good
that west winds will settle over the metro early afternoon with
occasional gusts 15-20kt late afternoon/early evening. Lofted
wildfire smoke may continue to affect slantwise visibility towards
sunset, though there should be no sfc restrictions. While TS/SHRA
will remain well northeast of terminals, there is some model
evidence that outflow winds will attempt to sweep into terminals
creating an earlier than usual easterly wind shift. However, there
is equal probabilities that outflow winds decay when reaching the
metro, so have only hastened the easterly switch slightly.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Wednesday afternoon under
mostly clear skies. Winds will follow a near persistence forecast
with directions varying between SE and SW and gusts around 25kt
common at KBLH.

&&

.FIRE WEATHER...
Above normal temperatures are expected over the next couple days
with moisture levels remaining fairly limited. Isolated afternoon
thunderstorms will remain possible mainly over the eastern Arizona
high terrain with dry lightning a possibility due to less than 10%
chances of wetting rainfall. As moisture increases by Thursday, rain
chances will increase and spread into the Arizona lower deserts.
Minimum afternoon humidity levels will mostly range between 15-20%
with fair to good overnight recoveries. Winds will continue to
follow diurnal trends with afternoon gusts up to 15-20 mph.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Wednesday for AZZ530-532-
     534-537>544-546-548>551-553>555-559.

CA...Extreme Heat Warning until 8 PM PDT Wednesday for CAZ562-563-
     566-567-569-570.

&&

$$

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