737
FXUS65 KPSR 231149
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
449 AM MST Sat Aug 23 2025

.UPDATE...Updated 12z Aviation Discussion.

&&

.KEY MESSAGES...

- Well above normal temperatures persist through the weekend,
  resulting in widespread areas of Major HeatRisk.

- Extreme Heat Warnings continue across the majority of the region
  through the weekend.

- Slight chances for showers and storms, mainly east of the Lower
  Colorado River Valley and west of Phoenix, exist through the
  weekend, with better rain chances moving into the region during
  the first half of next week.

- Temperatures cool to below normal during the middle of next week.

&&

.SHORT TERM /Today through Sunday/...
The overall synoptic pattern remains largely unchanged and is
expected to remain that way through the weekend. RAP 500mb
analysis shows the subtropical ridge centered over southern Utah
with heights around 592 dm early this morning. Models continue to
show heights fluctuating between 592-594 dm through the weekend.
This will cause temperatures to hold fairly steady today and
tomorrow. Afternoon high temperatures are forecasted to be in the
105-113 degree range, with morning low temperatures forecasted to
continue to range from the mid 80s to low 90s across the lower
deserts. The combination of these temperatures will result in
widespread Major HeatRisk across the lower deserts. Due to this
the Extreme Heat Warning will remain in effect across the lower
deserts through the weekend. So, everyone should continue to
practice smart heat safety to avoid any heat related health
issues. If you have outdoor plans this weekend, consider altering
them to avoid the heat of the day and make sure to drink plenty of
water and take frequent breaks, in the shade if possible.

Best chances (15-35%) for shower and storms in our CWA through the
weekend will be across western portions of the CWA, particularly
in SW AZ. Showers and storms today are expected to develop in the
higher terrain north of Phoenix and in western Sonora, Mexico and
southern AZ. Steering flow today will be out of the east, so it
won`t be as favorable to push storms into the lower deserts. However,
the environment across SW AZ will be favorable to support storms.
Higher PWATs (1.4-1.6"), MUCAPE values around 1000-2000 J/kg, and
DCAPE values around 1000-1500 J/kg. So if a deep outflow or
multiple colliding outflows move through the environment would
support storm development. HREF probabilities are less than 50%
for seeing winds in excess of 35 mph today, with the highest
probabilities across SW AZ. As for eastern portions of the CWA,
mid-level water vapor imagery reveals a slot of dry air, from the
Plains, has moved into southeastern and central portions of AZ,
including the Phoenix Metro. In order for any showers or storms to
form in these areas they will have to overcome this mid- level
dry air, which will likely take multiple outflow boundaries.
Models and the SPC mesoanalysis for PWATs show that the higher
PWATs (1.4-1.6") will be across SW AZ and SE CA through the
weekend, which is where there are better storm chances. Similar
MUCAPE and DCAPE values are expected across SW AZ tomorrow. Models
indicate that the steering flow will shift slightly to be more
SE`rly, which would better support storms, from Mexico and/or
southern AZ moving into the lower deserts of SW AZ. HREF
probabilities for higher wind speeds increase tomorrow. They
currently show a 50-70% chance of winds greater than 35 mph and a
10% chance of winds greater than 58 mph, with the highest
probabilities once again across SW AZ.

&&

.LONG TERM /Monday through Friday/...
For the first half of next week the overall synoptic pattern will
shift, with the subtropical high weakening and shifting to the south
and east. Ensembles continue to be in good agreement that by the
beginning of next week the overall synoptic pattern will shift, with
the subtropical high weakening and shifting to the south and east.
This shift will occur due to two troughs, one digging into the
east/north east portion of the US and another trough digging off the
Pacific coast. This will do a couple things for our region. One it
will shift the steering flow to be out of the south/southeast, which
will promote better moisture into our region and thus an increase in
shower and storm activity. And two, the weakening of the high will
lead to cooling temperatures.

Global ensembles continue to disagree on the amount of moisture,
with a difference of about 0.2" between the GEFS and ECMWF ensemble.
Both show PWATs peaking on Tuesday. The GEFS shows PWATs peaking
around 1.4-1.7", whereas the ECMWF ensemble shows PWATs peaking
around 1.6-1.9". Either way, the first half of next week looks to be
rather active. Monday may end up being more of a transition day,
with better chances on Tuesday and Wednesday, with Tuesday currently
looking the best. With the combination of lowering heights aloft and
increased cloud cover, from the increased PoPs, temperatures are
expected to cool through the middle of next week. Afternoon high
temperatures are forecasted to cool to near to slightly above normal
on Monday (104-108 degrees across the lower deserts) and fall below
normal Tuesday and Wednesday (forecasted highs of 98-103 degrees
across the lower deserts). Morning lows will also be cooling next
week, with morning lows forecasted to fall into the mid 70s to mid
80s across the lower deserts by the middle of next week. Depending
on the exact timing and coverage of showers and storms next week,
temperatures could be even cooler than currently forecasted.

By the end of the workweek, flow overhead will become more
SW`rly/W`rly, which will in turn cause us to see drying conditions.
Overall, ensembles show PWATs generally in the 1.2-1.4" range by
Thursday and in the 0.8-1.1" range on Friday. With the drying
conditions and no forcing, our shower and storm chances will be
coming to an end across the CWA. While, heights aloft won`t change
too much to end the week, with the decreasing shower and storm
chances we will see a return of mostly clear skies. This will result
in temperatures warming a few degrees. Current forecasted afternoon
high temperatures are in the 98-104 degree range across the lower
deserts for Thursday and Friday, which are still a few degrees shy
of the daily normals for this time of year.

&&

.AVIATION...Updated at 1150Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation concerns through tonight. Distant outflows from
shower/storm activity cannot be ruled out for this evening, but
probabilities are too low of anything impactful worth advertising
in this package. Generally elevated winds relative to the norm
early this morning across all terminals have some differences in
wind directions as some weak outflows have moved through the metro
over the last couple of hours. Anticipating these generally
southerly to southwesterly component winds to persist over the
next few hours before weaker and more variable winds settle
through most of the morning. Westerly to northwesterly component
winds will then be the dominant direction for the afternoon and
evening hours, sans an outflow from a different direction. FEW-SCT
skies will prevail for the most part with cloud decks aoa 10 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns expected through tonight. Wind trends
will be similar to the past 24 hours with directions generally
varying between SE and SW at both terminals with wind speeds
generally AOB 10kts, but periods of higher speeds is still
possible. Some isolated showers and storms may develop in the
vicinity of at least KBLH later this afternoon and evening, but
probabilities are too low to include any change groups or
PROB30`s/TEMPO`s for this TAF package.

&&

.FIRE WEATHER...
Temperatures will remain around 4-7 degrees above normal through
the weekend. Daily thunderstorm chances will continue through the
weekend with monsoonal activity expected to expand to include the
western districts. Best chances for storms this weekend will be
across the western districts. Lightning, locally heavy rainfall,
and gusty erratic outflow winds will be the primary threats with
thunderstorms. Chances for seeing outflows in excess of 35 mph
for tonight are less than 50%, with the highest probabilities
across SW AZ. Probabilities increase tomorrow, with the HREF
showing a 50-70% chance of winds in excess of 35 mph and a 10%
chance of winds in excess of 58 mph, with the highest
probabilities once again across SW AZ. MinRHs will be around
15-25% through the weekend, while Max RHs will be around 40-50%
for most areas. Shower and storm chances increase even more during
the first half of next week. MinRHs improve to 20-40% during the
first part of next week, with overnight recoveries improving to
50-70% for the first half of next week. By the end of next week we
will start drying out again, seeing storm chances come to an end
along with RHs decreasing (minRHs: 15-35% and maxRHs: 30-60% for
Thursday and Friday, with the highest RHs across the eastern
districts).

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530>555-559.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ560>570.

&&

$$

SHORT TERM...Berislavich
LONG TERM...Berislavich
AVIATION...Young
FIRE WEATHER...Berislavich