San Luis, Arizona 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

621
FXUS65 KPSR 290511
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1011 PM MST Sat Jun 28 2025

.UPDATE...Updated 06Z 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...
Increasing heights aloft 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. 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 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 it is 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 to a big downtrend in any
monsoon activity.

&&

.AVIATION...Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Westerly winds will continue into the overnight hours with speeds
aob 8 kt. Winds at KIWA will do their typical shift to SE`rly
around 10Z before going back westerly late tomorrow morning. At
the other TAF sites, winds may not go fully easterly overnight and
may just be light and variable. Westerly winds will redevelop at
all TAF sites by late tomorrow morning/early tomorrow afternoon.
Gusts up near 20 kt are anticipated again tomorrow afternoon and
early evening. Skies will remain mostly clear with FEW clouds aoa
10 kft tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
Westerly winds at KIPL will go light and variable tomorrow morning
and then become westerly again tomorrow night. At KBLH, winds will
favor a SW component before going southerly tomorrow afternoon
before going southwesterly again tomorrow evening. Wind speeds at
both terminals will be aob 10 kt. 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...
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 increase
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>555-559-560-562.

     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/95
AVIATION...Berislavich
FIRE WEATHER...Kuhlman/95