352
FXUS65 KPSR 291735
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1035 AM MST Sun Jun 29 2025

.UPDATE...18Z Aviation Discussion.

.KEY MESSAGES...

- Hot and dry conditions will persist through the first half of
  the week as lower desert high temperatures top out between 110
  and 115 degrees through Tuesday.

- Extreme Heat Warnings are in effect for the Phoenix metro
  starting today through Tuesday with the warning in effect for
  the rest of the lower deserts Monday and Tuesday as areas of
  Major HeatRisk develop.

- An increase in moisture will lead to increased chances of
  showers and thunderstorms during the middle and latter half of
  the week across portions of AZ, with the best chances for
  activity confined across the higher terrain areas.

&&

.DISCUSSION...
The main forecast concern through the first half of the week will
be the extreme heat conditions expected to materialize as a
strengthening subtropical ridge will set up near the AZ/NM border
through Monday and near the Four Corners Region by Tuesday with
500 mb height fields increasing to 591-594dm. The strengthening
ridge of high pressure is aided in part by an upper-level low
situated off the west coast of southern CA. Afternoon high
temperatures today across the lower deserts will range between
111-114 degrees with readings slightly hotter on Monday as values
are expected to peak between 112-116 degrees. As a result of these
temperatures, areas of Major HeatRisk are expected to materialize
with the greatest concentration of Major HeatRisk expected for
mainly the Phoenix area today and then expanding across the rest
of the lower deserts as well as some of the higher terrain zones
of eastern Maricopa and southern Gila Counties on Monday. As a
result, Extreme Heat Warnings are in effect. For the Phoenix area,
there is a decent shot (>60%) of the daily record high of 115
degrees being tied/broken on Monday. Temperatures on Tuesday are
expected to slightly decrease, however, still high enough for
widespread areas of Major HeatRisk to continue and thus the
Extreme Heat Warnings have been extended for all of the lower
desert locations.

As the subtropical ridge settles across the Four Corners Region
and the aforementioned upper-level low settles near the southern
CA coast Tuesday through early Wednesday, a south to southeasterly
flow will settle across most of Arizona, helping to advect modest
moisture northward. Therefore, an increase in shower and
thunderstorm activity is likely starting on Tuesday across the
eastern Arizona higher terrain areas with better coverage on
Wednesday. Activity across the higher terrain areas could direct
some outflows into the lower deserts both days, especially during
the evening hours, with gusty winds and blowing dust across the
dust prone areas.

The main challenge with this forecast and one that is still of
low confidence is the potential for thunderstorm activity to
materialize across the lower deserts of south-central AZ as
moisture levels are expected to be marginal at best with the
latest EPS and GEFS now showing PWATs only peaking at around
1.2-1.3" for the Phoenix area. This downward trend in moisture is
due to the latest trend in the model guidance showing the upper-
level low tracking further south and slightly faster, decreasing
the residence time of the deeper moisture advection into the
region. Nevertheless, there is the potential for some thunderstorm
activity to materialize, especially late Wednesday night through
Thursday as the upper-level forcing from the jet associated with
the upper-level low approaches from the west, which may compensate
for the marginal moisture in place. It is during this time frame
of Wednesday night through Thursday when NBM PoPs are at its
highest across the lower deserts of south-central AZ, ranging
between 20-40%. As the trough continues to move further inland
through much of the Desert Southwest, the westerly flow aloft is
likely to scour out most of the moisture, leading to a downward
trend in monsoonal thunderstorm activity starting on Friday and
lasting into next weekend.

With the decreasing heights aloft from the incoming trough,
temperatures during the middle to latter half of the week are
expected to take a noticeable downward trend. Forecast highs by
Wednesday are expected to be near normal, before dropping a couple
of degrees below normal Thursday and Friday. Thereafter, as the
trough lifts away and upper-level height fields start to increase
once again by next weekend, temperatures will be on slight upward
trend. The good news is that temperatures should remain near
normal with no extreme heat conditions expected through the 4th of
July Holiday Weekend.

&&

.AVIATION...Updated at 1735Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Westerly winds are forecast at all TAF sites this afternoon with
afternoon gusts up to 20 kts at times. Skies will remain mostly
clear with FEW clouds around 12-15 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
Westerly winds are likely for KIPL through the period with KBLH
seeing light and variable winds with a generally southerly
direction during the afternoon/evening hours returning to a
westerly direction around 00Z. Skies will remain mostly clear.
Lofted smoke/haze may at times lower slantwise visibility during
the late afternoon/evening hours, mainly at KIPL.

&&

.FIRE WEATHER...
Very hot and dry conditions will persist during the next couple of
days as lower desert highs exceed 110 degrees. MinRH values
through Monday will range between 5-15% with poor overnight
recoveries. The overall wind pattern will continue to follow the
familiar diurnal trends with the typical afternoon upslope
breeziness. Starting on Tuesday, increasing moisture will lead to
higher relative humidities as well as increasing chances for
shower and thunderstorm activity across the higher terrain areas.
There will be some initial concerns for dry lightning activity
before a further increase in moisture levels leads to a better
potential for wetting rains later in the week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM Monday to 8 PM MST Tuesday for
     AZZ530>536-538-539-553-554-559.

     Extreme Heat Warning until 8 PM MST Tuesday for AZZ537-540-
     542>544-546-548-550-551.

     Extreme Heat Warning from 10 AM to 8 PM MST Monday for AZZ541-
     545-547-549-552-555-556-560>562.

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

&&

$$

DISCUSSION...Lojero
AVIATION...Kuhlman/95
FIRE WEATHER...Lojero