269 
FXUS65 KPSR 221204
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
504 AM MST Fri Aug 22 2025

.UPDATE...Updated 12z Aviation Discussion.

&&

.KEY MESSAGES...

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

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

- Strong to severe thunderstorms are possible across south-central
  Arizona, southwest Arizona, and the Lower Colorado River 
  Valley, with the main threat being strong outflow winds.

- Better rain chances move into the region during the first half
  of next week.

&&

.SHORT TERM /Today through Sunday/... 
The overall synoptic pattern has started to finally shift as of 
early this morning. The subtropical high pressure has weakened 
slightly (594 dm) and has shifted westward across southern Utah. 
The high pressure is expected to remain in this general region 
through the weekend with the strength of it largely fluctuating 
around 593-595 dm. With the slight weakening of the high, 
afternoon high temperatures will also slightly decrease. 
Forecasted high temperatures will be in the 106-113 degree range 
through the weekend across the lower deserts. Across the higher 
terrain areas, highs will be in the 98-106 degree range today and 
cool to 95-103 degrees this weekend due to the high shifting 
westward. Morning low temperatures will remain in the mid 80s to 
low 90s through the weekend across the lower deserts as well. 
Morning lows may also end up being warmer than currently 
forecasted depending on any residual cloud cover from thunderstorm
activity from the previous day. With the combination of these 
temperatures, Major HeatRisk, with areas of localized Extreme 
HeatRisk, will remain widespread across much of the region today 
and through the weekend. Although this weekend the HeatRisk 
decreases to moderate across the higher terrain. Due to this the 
Extreme Heat Warning remains in effect through this weekend for 
portions of the region. Today's Extreme Warning includes the lower
deserts and higher terrain areas, tomorrow's Extreme Heat Warning
is just across the lower deserts, and Sunday's Extreme Heat 
Warning is just the greater Phoenix Metro. However, Sunday's may 
need to be expanded across the rest of the lower deserts. Everyone
should continue to follow the proper heat safety precautions, 
including limiting time outdoors and staying hydrated, to avoid 
heat- related issues. 

Even with the westward shift of the high pressure system, it remain 
a favorable pattern for monsoon activity across our area. It 
actually increases monsoonal across the western deserts. Favorable 
easterly steering flow, of 15-20 kt. remains in place. Hi-res models 
consistently show scattered showers and storms firing up this 
afternoon in the higher terrain, both north and south of Phoenix, 
and pushing into the lower deserts this evening. The models do 
differ on the exact placement and coverage of these storms. 
However, the environment is favorable for isolated to scattered 
showers and storms to survive into the lower deserts. However, 
there are some areas, particularly around the Phoenix Metro, that 
are worked over from last nights storms. So these areas may not 
see much, if any activity, tonight. Paintball plots support this 
by showing activity skipping around the Phoenix Metro and 
congealing in the deserts of southwestern AZ. The environment 
will once again support strong to severe storms tonight, and the 
SPC has placed south-central AZ, southwestern AZ, and the Lower 
Colorado River Valley in a marginal risk for severe storms today, 
with the main threat being severe winds (>58 mph). PWATs early 
this morning are around 1.3-1.5" and are expected to increase to 
around 1.5-1.7" later today. Forecast soundings also show MUCAPE 
values greater than 1000 J/kg and DCAPE values around 1500-2000 
J/kg, which further support the potential for severe storms. The 
HREF shows a 30-50% chance of winds greater than 35 mph across 
south- central Arizona, southwest Arizona, and the Lower Colorado 
River Valley. The HREF also shows a bullseye in the lower deserts 
of southwestern Arizona, where there is a 10% chance of winds 
greater than 58 mph. These strong winds will be capable of 
generating areas of blowing dust, and a Blowing Dust Advisory may
need to be issued later this morning. 

With the overall synoptic pattern largely remaining unchanged 
through the weekend, and easterly steering flow in place, it will 
promote the continuation of daily thunderstorm chances across the 
region. CAMs show similar patterns for shower and storm activity 
over the next two days as is expected tonight (storms developing 
in the higher terrain of Arizona and moving into the lower 
deserts). However, each day's activity will rely heavily on how 
the previous day turns out. Either way, the main threats will be 
strong gusty winds (main threat), excessive lightning and 
localized heavy downpours (leading to localized flooding 
concerns). The HREF does show a 30-50% chance of winds greater 
than 35 mph for tomorrow.

&&

.LONG TERM /Monday through Thursday/... 
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 two, the weakening of the high will lead to cooling 
temperatures. 

As for the changing steering flow and increase in moisture, that 
will bring better chances for showers and storms across much of the 
area for the first half of the workweek. So, we may see more 
scattered to potentially widespread activity. The ensembles do still 
disagree on the amount of moisture that will move into our region. 
The GEFS keeps PWATs in the 1.5-1.6" range, whereas the ECMWF 
ensemble increases PWATs to the 1.7-1.9" range. Due to this, the 
ECMWF does have better PoPs across our region than the GEFS. 
Either way should be ample moisture to at least produce isolated 
to scattered activity across portions of the CWA. The NBM was 
running hot still, so did lower those slightly. Stay tuned for 
updates as we get closer to next week. 

As for the cooling temperatures, the weakening of the ridge and 
lowering heights (588-592 dm) aloft within of itself will lead to
cooling temperatures. But showers and storms, and their 
associated cloud cover, will also help to dampen temperatures. 
Afternoon high temperatures are forecasted to cool to near to 
slightly above normal on Monday, with temperatures falling below 
normal for the middle of the workweek (Tuesday-Thursday). 
Forecasted high temperatures range from 104-109 degrees on Monday 
and 94-102 degrees Tuesday-Thursday across the lower deserts. 
Morning lows are also expected to fall back to near normal and are
forecasted to range from the upper 70s to mid 80s. With the 
cooling temperatures we will also see HeatRisk decreasing, 
becoming widespread moderate on Monday and widespread minor 
Tuesday-Thursday. While models are in good agreement on the 
overall pattern for the beginning of the week, they start to 
differ, quite a bit, by the middle of the week. This discrepancy 
is mainly driven by the aforementioned trough off the Pacific 
coast and how far south it will dig and how far inland it might 
push. This discrepancy can be seen in the IQR temperature scores. 
The maxT IQR scores are 6 for Tuesday, 10 for Wednesday, and 12 
for Thursday. Either way, increasing storm chances and cooling 
temperatures are expected for the first half of next week. 

&&

.AVIATION...Updated at 1200Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: 
Shower and thunderstorm chances, with gusty winds and blowing dust
potential, anticipated to be mainly this evening is the most
prominent aviation impact for the forecast period. A number of
outflows moving across the metro area early this morning is
causing some erratic and inconsistent wind directions, thus
lowering forecast confidence in the predominant wind direction,
but as of recent winds are mainly southerly. Sans another outflow
emanating out of a different direction, anticipating winds to
remain southerly (generally 150v220) into the morning hours prior
to a more predominant southwesterly to westerly component
developing by the afternoon. While VFR conditions will prevail
through this afternoon, there may be some lingering slantwise
visibility restrictions this morning due to lingering dust from
last nights activity. SCT-BKN skies should slowly clear through 
the morning hours, prior to higher terrain convective activity 
increasing the cloud coverage again late this afternoon and into 
the evening, with SCT-BKN skies again into the overnight hours.

Heading into this evening, while likely that at least one outflow
with gusty winds (30-50% chance of gusts exceeding 30 knots) will
impact the terminals, confidence is low on what direction, which 
has implications on flight configurations (any easterly
direction) and blowing dust potential (southerly to southeasterly
direction). Currently have moved up the timing of outflow 
potential, anticipated between 00-02z, with PROB30 -SHRA following
between 03-06z as chances still remain generally low of any 
terminal seeing SH/TS conditions. General wind evolution post- 
outflow and showers/storms remain low confidence through the rest 
of the period.

Southeast California/Southwest Arizona including KIPL and KBLH: 
No major weather issues will exist through tonight under passing 
mid/high cloud decks. Wind trends will be similar to the past 24 
hours with directions generally varying between SE and SW. Periods
of variability or nearly calm conditions will be common during 
the morning hours.

&&

.FIRE WEATHER...
Temperatures will remain around 4-7 degrees above normal through
the weekend, cool to near normal on Monday, and cool below normal
for the middle of next week. The overall pattern for storms
through the weekend will be relatively similar, with scattered
showers developing across the higher terrain during the afternoon
and pushing into the lower deserts during the evening. Each day's
activity will depend on how the previous day shakes out. The main
threats with these storms will be strong, gusty winds (main
threat), excessive lightning, and localized heavy downpours. HREF
probabilities, for today, show a 30-50% chance of winds exceeding
35 mph across south-central AZ, SW AZ, and the Lower CO River 
Valley and a 10% chance of winds exceeding 58 mph over SW AZ.
Shower and storm chances increase even more during the first half
of next week. MinRHs will be around 15-20% through the weekend,
improving to 20-30% on Monday, and 25-40% Tuesday-Thursday.
Overnight recoveries will be fair through the weekend and good
during the first half of next week.

&&

.CLIMATE...

Record highs later this week:

Date       Phoenix          Yuma          El Centro
----       -------          ----          --------- 
8/22     113 in 2011     115 in 1969     117 in 1969

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Saturday for AZZ530>536-538-
     539-541-545-547-549-552>555-559.

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

     Extreme Heat Warning until 8 PM MST this evening for AZZ556-560-
     562.

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

&&

$$

SHORT TERM...Berislavich
LONG TERM...Berislavich 
AVIATION...Young/Benedict
FIRE WEATHER...Berislavich
CLIMATE...18