434
FXUS65 KPSR 200552
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1052 PM MST Tue Aug 19 2025

.UPDATE...Updated 6Z Aviation Discussion.

&&

.KEY MESSAGES...

- High pressure will strengthen over the region this week, causing
temperatures to climb to near record levels during the latter half
of the workweek, which will result in the return of widespread major
HeatRisk.

- Extreme Heat Warnings are in effect across the majority of the
region Wednesday through Friday.

- Monsoon thunderstorm activity will remain primarily confined to
  the high terrain of E and SE Arizona through the next day or so
  before rain chances expand to the lower deserts by the end of
  the week and into the beginning of next week.

&&

.SHORT TERM /Today/...
Early afternoon RAP analysis showed the subtropical ridge of high
pressure now centered near the Four Corners with 500 mb heights now
rising to around 594-596 dm across the area. This will lead to a
slight bump in our highs today with temperatures expected to top out
around 106-111 degrees across the lower deserts through the rest of
the afternoon. These warmer temperatures today is promoting
widespread Moderate HeatRisk, so everyone, particularly those
sensitive to the heat, should exercise the proper precautions to
avoid heat-related health issues.

The relocation of the subtropical high near the Four Corners is
promoting E/SE mid level flow and is helping to advect better
moisture into the area. The latest SPC mesoanalysis shows PWATs
across south-central Arizona have climb to around 1.1-1.3", while
MUCAPE has increased to around 500-1000 J/kg across southern Gila
County. The increase in moisture and instability has already led
to a few afternoon showers and thunderstorms across southern Gila
County with chances persisting into this evening. Given a dry
subcloud layer and DCAPEs climbing up to around 1000 J/kg, strong
erratic outflow winds will be possible with any stronger
thunderstorms that develop across southern Gila County through the
rest of this afternoon into the evening. The latest HREF
indicates about a 30-50% chance for seeing outflow wind gusts in
excess of 35 mph. Any outflows and thunderstorm activity will
diminish as they progress westward toward the lower deserts.

&&

.LONG TERM /Wednesday through Tuesday/...
Heading into the latter half of the workweek and into the weekend,
the overall synoptic pattern will not change much. The subtropical
ridge will remain in place over the Four Corners region, but will
strengthen to around 596-598 dm, peaking during the Wednesday-
Thursday time period. With the strengthening ridge, afternoon high
temperatures, Wednesday-Friday, will warm into the 108-116 degree
range across the lower deserts and into the 98-108 degree range
across some of the higher terrain areas. Forecasted high
temperatures on Thursday and Friday are even within a few degrees of
the current daily records for our three climate sites (Phoenix,
Yuma, and El Centro). There will also be little to no overnight
relief as morning low temperatures are forecasted to be in the upper
80s to low 90s. Lows of this magnitude are also near record warm
readings for our three climate sites. The combination of these high
and low temperatures will result in widespread Major to locally
Extreme HeatRisk across much of the area. The Extreme Heat Warning
remains in effect for much of the region for Wednesday through
Friday.

Ensemble guidance continues to show the ridge weakening slightly
(around 594 dm) this weekend. This weakening will result in
temperatures slightly cooling off. Afternoon high temperatures
are forecasted to be in the 106-112 degree range across the lower
deserts this weekend. Morning lows are also forecasted to remain
on the warmer side, with morning lows currently forecasted to
range from the mid 80s to near 90 degrees this weekend. These
temperatures don`t cool off enough to get rid of all of the Major
HeatRisk, as a good chunk of the lower deserts remain in the
Major category this weekend. So, the Extreme Heat Warning may need
to be extended through this weekend. However, with some
uncertainty still surrounding the increase in moisture expected
this weekend and thunderstorm activity, the decision to extend the
Extreme Heat Warning will need to be made later this week when
there is more confidence in this weekend`s forecast.

With the subtropical high remaining virtually stationary over the
Four Corners region for the latter half of the workweek and into the
weekend, this will provide the region with a much better set up for
an increase in monsoonal activity. The flow overhead will become
deep and persistent E`rly/SE`rly, which will lead to increasing
moisture across the region, which in turn will lead to increasing
shower and thunderstorm chances, including over the lower
deserts. Ensemble members remain in good agreement that mixing
ratios will increase to around 10 g/kg with PWATs rising into the
1.4-1.7" range. This will support daily thunderstorm chances
(30-50%) across the higher terrain, with rain chances increasing
to around 15-40% across the lower deserts. Ensembles continue to
show a slight shift W-SW of the subtropical high Friday and
Saturday. This slight shift will concentrate PoPs (20-50%) over SW
AZ and SE CA on Friday and Saturday, leaving a hole of lower PoPs
(10-30%) over the greater Phoenix Metro area. Due to the hit-or-
miss nature of shower and thunderstorm activity, it is difficult
to discern where the highest rainfall totals will occur and this
will hopefully become more clear over the next few days.

By the end of the weekend and heading into early next week, the
subtropical high will weaken even more and shift S/SE. This will
allow for temperatures to cool off, with forecasted highs returning
to near to slightly above normal by Monday and falling slightly
below normal on Tuesday. This shift in the subtropical high will
cause the flow overhead to become more S/SE. And will shift better
PoPs into the south-central AZ lower deserts, including the Phoenix
Metro. Current NBM PoPs show 20-40% across the south-central AZ
lower deserts for the beginning of next week. However, with this 5-7
days out there remains an ample amount of uncertainty and each day`s
thunderstorm chances will heavily rely on how thunderstorms the
previous day shakes out.

&&

.AVIATION...Updated at 0552Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Primary aviation impacts over the next 24-30 hours will be strong
outflow(s) from the E-NE Wednesday afternoon and evening, with
slight chances (10-20%)for VCSH/VCTS, potential slantwise
visibility impacts Wednesday evening from wildfire smoke, and
isolated weak virga showers tomorrow morning. Winds will still
tend to follow typical diurnal patterns through Wednesday
afternoon, but confidence in a sustained westerly shift is low.
Variability may persist up until the passage of an outflow from
the E-NE between 23-04Z. Hi-res models support 50% odds of peak
outflow winds exceeding 30 kts tomorrow. FEW to SCT mid and high
clouds will be common through the TAF period, with BKN coverage in
the evening and overnight hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather issues will exist through the forecast period
under periods of FEW to SCT mid to high clouds. Winds will follow
typical diurnal patterns with a predominant S to SW wind at KBLH
and E to SE winds at KIPL, with a period of W from late evening
through early morning. Periods of light and vrb winds are expected
at both terminals in the morning hours as well.

&&

.FIRE WEATHER...
Above normal temperatures and mostly dry conditions will continue
today. Much hotter temperatures are anticipated mid to late week
as highs approach record levels. Winds will continue to follow
diurnal upslope/downvalley patterns with afternoon gusts in the
15-20 mph range. Relative humidity will bottom out around 15-25%
through the week, with poor overnight recovery across the western
districts and fair overnight recovery in the eastern districts.
Thunderstorm activity will likely remain confined to the higher
terrain of E and SE AZ today and tomorrow before expanding to the
lower deserts by the end of the week. The chances for wetting
rainfall will also increase across the foothills and higher
terrain of southcentral AZ later this week.

&&

.CLIMATE...

Record highs later this week:

Date       Phoenix          Yuma          El Centro
----       -------          ----          ---------
8/20     113 in 2019     114 in 1982     114 in 1969
8/21     114 in 2019     115 in 1969     117 in 1969
8/22     113 in 2011     115 in 1969     117 in 1969

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Friday for
     AZZ530>556-559-560-562.

CA...Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Friday for
     CAZ560>570.

&&

$$

SHORT TERM...Smith
LONG TERM...Berislavich
AVIATION...Benedict
FIRE WEATHER...Berislavich
CLIMATE...18