073
FXUS65 KPSR 281143
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
443 AM MST Sat Jun 28 2025

.UPDATE...Updated 12z Aviation Discussion...

&&

.KEY MESSAGES...

- Hot and dry conditions are expected into early next week with
  lower desert high temperatures topping out mostly between 110
  and 115 degrees for Sunday through Tuesday

- Extreme Heat Warnings have been issued for the Phoenix metro
  Sunday through Tuesday with the rest of lower deserts in effect
  only for Monday as areas of Major HeatRisk develop

- An increase in moisture by the middle of next week is likely to
  lead to chances for showers and thunderstorms for portions of
  Arizona, favored more across higher terrain areas

&&

.DISCUSSION...
The sub-tropical ridge has begun to recenter itself directly over
the Desert Southwest with H5 heights now around 590-591dm. The
increasing heights aloft since Thursday will continue to help
temperatures to heat up this weekend with readings already
expected to top out around 110 degrees today. The ridge should
strengthen a bit further Sunday into Monday peaking at 591-593dm,
but still below the 90th percentile of climatology. Forecast
temperatures during the peak strength of the ridge have trended
upward over the past few model runs with Sunday now showing
111-114 degrees and Monday at 112-116 degrees. Temperatures are
likely to begin to lower starting Tuesday, but only by a degree or
two as a dry Pacific low approaches the region from the west. Due
to the even hotter trends within the models, the areas of Major
HeatRisk have expanded, particularly on Monday which now show at
least localized Major HeatRisk throughout all of the lower
deserts. As a result, we have decided to expand the Extreme Heat
Warning westward through southwest Arizona and much of southeast
California. Daily record highs are mostly out of reach, but the
115 degree record on Monday for Phoenix is very likely (~80%) to
at least be tied and/or broken (~50%).

The Pacific low that will approach our region early next week is
set to begin taking shape west of southern California already by
tonight into Sunday. Guidance has struggled with this weather
feature, but now seems to agree it will have a greater influence
on our weather by Tuesday and Wednesday. The positioning of the
low just to our west and the high center shifting more to our
northeast over the Four Corners area should allow for a modest
southeasterly moist flow into at least southeast Arizona by
Tuesday. Moisture should increase enough for some isolated showers
or a few thunderstorms across the eastern Arizona higher terrain
as early as Tuesday afternoon, but more likely by Wednesday.
Either or both of those days should only result in rain chances
over the higher terrain, but it may be possible to direct storm
outflows into the south-central Arizona lower deserts. A south
southeast steering flow on Tuesday is somewhat favorable, but at
this moment storm coverage is not likely to be very high. By
Wednesday, storm coverage over southeast and eastern Arizona is
likely to increase, but the steering flow is likely to switch out
of the south southwest which is definitely less favorable for any
activity reaching the lower deserts.

Beyond Wednesday, guidance is even more murkier with each new
model run disagreeing on how much and how far west the moisture
will reach. Forecast confidence for any shower or thunderstorm
chances into the south-central Arizona lower deserts is still
fairly low for late next week as it will largely depend on the
available moisture and the positioning of expected jet forcing
from the trough situated just to our northwest. Any other
forcing from any potential subtle sub-tropical waves or mesoscale
features is still unknown at this time. The south southwesterly
steering flow (non-favorable for the lower deserts) will however
most likely stay in place through the rest of next week. The NBM
PoPs are still pointing at Thursday being the best day for more
widespread chances (30-40%) across south-central Arizona, but
even that is of low forecast confidence. There are several pieces
that will have to come together for our area (south-central
Arizona specifically) to have a active monsoon day later next
week, and right now we are uncertain whether it will turn out that
way. Of higher certainty is the cooler temperatures for the
latter half of next week as the trough should lower heights aloft
while lower level moisture increases. Forecast highs by Wednesday
should be closer to normal, before potentially dropping 3-5
degrees below normal by around Thursday. Ensembles then suggest
the trough will move further inland encompassing all or most of
our region by around next Saturday. If this scenario were to
occur, it would likely dry out much of our area leading a big
downtrend in any monsoon activity.

&&

.AVIATION...Updated at 1140Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
No major aviation weather concerns under mostly clear skies can be
expected throughout the TAF period. Winds will continue to follow
the familiar diurnal tendencies, although confidence is low of a
full easterly shift occurring at KPHX early this morning with wind
directions expected to be more variable. Confidence is high that
an early westerly wind component will take hold by around 15-16z.
Overall wind speeds will range between 8-12 kts with some
occasional afternoon/early evening gusts between 15-20 kts.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns under clear skies can be
expected throughout the TAF period. Wind directions will favor a
S/SE component during the daytime hours followed by a W/SW
component during the evening/overnight hours. Overall wind speeds
will remain aob 10 kts, although some occasional afternoon gusts
near 20 kts can be expected at KBLH. Lofted smoke/haze may at
times lower slantwise visibility during the late afternoon/evening
hours.

&&

.FIRE WEATHER...
Strong high pressure over the region will push lower desert highs
to over 110 degrees by Sunday as overall hot and dry conditions
persist into early next week. Expect little change in humidity
trends through Monday as MinRH values continue to range between
5-15% each day and overnight recoveries stay between 20-35%.
Winds will follow familiar diurnal trends with typical afternoon
breeziness, gusting mainly between 15-20 mph. Eventually, the
weather pattern will become more favorable for increasing
moisture and at least some scattered high terrain showers and
thunderstorms by around next Tuesday and Wednesday. This may
initially result a day or two of dry lightning concerns before
moisture and rainfall chances increases later next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM to 8 PM MST Monday for
     AZZ530>536-538-539-541-545-547-549-552>555-559-560.

     Extreme Heat Warning from 10 AM Sunday to 8 PM MST Tuesday for
     AZZ537-540-542>544-546-548-550-551.

CA...Extreme Heat Warning from 10 AM to 8 PM PDT Monday for CAZ562-
     565>567-569-570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Young/Kuhlman