284
FXUS65 KPSR 042300
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
400 PM MST Mon Aug 4 2025
.UPDATE...Updated Aviation Discussion
&&
.KEY MESSAGES...
- A widespread extreme heat episode is expected mid to late week
with lower desert highs likely to approach or exceed 115
degrees, around 10 degrees above normal for early August.
- Dry conditions will prevail across the forecast area, but rain
chances will gradually be introduced to the Eastern Arizona high
terrain and far southeastern Arizona during the middle of the
week.
&&
.SHORT TERM /Today through Tuesday/...
Mid-level wv imagery shows a trough that has pushed into the
Intermountain West, enhancing southwesterly flow over the Great
Basin and Northern AZ. As this trough pushed further inland, the
center of the subtropical high that was over Southern AZ has
shifted eastward into NM. With this shift, some amount of S/SE`rly
flow has been reintroduced to Southeastern AZ, and so enough
moisture has crept in to allow some cumulus buildups over
prominent terrain features of Santa Cruz and western Cochise
Counties. However, much of the state remains cloud-free today.
Under stable midlevel heights this afternoon, highs will peak
within a degree or two of what was observed yesterday, near or
just above 110F.
Ensembles show that the center of the midlevel anticyclone will
remain over NM through the middle of the workweek, however, the
high will expand to encompass the entire Desert Southwest and
build upwards of 597 dam by end of day Tuesday. As the high
expands and strengthens, temperatures will start to heat up
Tuesday, with latest NBM forecasting highs perhaps a couple
degrees warmer compared to this afternoon. As a result, anticipate
Major HeatRisk to become more widespread across South-Central AZ.
Meanwhile, moisture (mostly above 700 mb based on GFS bufr
soundings) will gradually increase into the middle of the week,
but ensemble mean PWATs generally remain below 80% of normal for
the time of year. Thus, chances for afternoon/evening t-storm
activity become reintroduced to the state but should remain
limited to far Southeastern AZ and the Eastern AZ high terrain
such as the Rim and White Mtns.
&&
.LONG TERM /Wednesday through Monday/...
Global ensembles show the center of the subtropical ridge of high
pressure migrating eastward into NM and strengthening during the
first part of the week. Ensemble and deterministic guidance continue
to show 500 mb heights climbing upwards of 598-600 dm by the middle
part of the week, which is in record territory for the
climatological period. With 500mb heights in that range, it will
drive temperature to further increase compared to the previous days.
This is expected to lead to high temperatures upwards of 113-118 by
Thursday across the lower deserts. These temperatures will challenge
multiple record highs, with Thursday expected to surpass the record
of 112, in Phoenix, by several degrees. Little overnight relief is
expected with warm low temperatures in the lower 90s in Phoenix. In
addition to daily record highs likely being challenged or broken,
Phoenix may very well tie or break the all-time hottest temperature
recorded during the month of August. The hottest Phoenix has ever
recorded in the month of August was 117 degrees which has happened 4
times (2011, 2015, 2020, and 2023). Guidance then show the very
strong ridge weakening for the end of the week as a trough
propagates through the northern Rockies. This will lead to
temperatures lowering, though still remaining above normal.
With significant heat in the forecast, widespread Major to Extreme
HeatRisk will increase across much of the forecast area by Wednesday
with Thursday expected to be the hottest day. Extreme Heat Warnings
are in effect for much of south-central Arizona through Friday. The
warning will expand to include the higher terrain east of Phoenix
Tuesday through Friday and the remainder of the CWA by Wednesday.
Everyone should take this heat seriously and take the proper heat
safety actions to avoid heat-related health issues.
The positioning of the ridge will allow for some southerly moist
advection in the later part of the week, however, ensemble guidance
only show PWAT values to climbing to around 70-80% of normal with
PWATs around an inch. The lack of better moisture will limit chances
for monsoon activity with the best chances for convection remaining
across the Rim and down into southeastern Arizona.
&&
.AVIATION...Updated at 2300Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Tuesday evening under
only a few passing cirrus decks. Trends in wind speeds and
directional shifts will be very similar to the past 24 hours
including a few gusts around 20kt through the remainder of the
afternoon/early evening and extended periods of variability around
sunrise and during the typical transitional timeframes.
&&
.FIRE WEATHER...
Unusually hot and dry conditions will continue for the start of the
week with temperatures gradually trending hotter through the middle
part of the week. MinRHs will fall into the 5-15% range through the
next couple of days, while MaxRHs range between 25-40% for most
areas. Winds will generally follow diurnal tendencies with typical
afternoon upslope gustiness. Temperatures will remain above normal
with lower desert highs mostly between 108-114 degrees through the
first half of the week, before increasing into the 113-118 degree
range during the middle portion of the week. Overall dry and hot
conditions will continue for the upcoming week with any rain chances
remaining mostly confined to the higher terrain east of Phoenix.
&&
.CLIMATE...
Record high temperatures this week:
Date Phoenix Yuma El Centro
---- ------- ---- ---------
Aug 4 116 in 2024 117 in 2021 119 in 2021
Aug 5 116 in 2023 116 in 2019 116 in 2019
Aug 6 114 in 2023 115 in 1995 114 in 2018
Aug 7 112 in 2012 114 in 1962 117 in 1970
Aug 8 116 in 2012 115 in 1940 115 in 2012
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Friday for
AZZ530>533-535-536.
Extreme Heat Warning until 8 PM MST Friday for AZZ534-537>544-
546-548>555-559.
Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Friday for
AZZ545-547-556>558-560>563.
CA...Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Friday for
CAZ560>570.
&&
$$
SHORT TERM...Whittock
LONG TERM...Ryan/Smith
AVIATION...18/RW
FIRE WEATHER...Ryan/Lojero
CLIMATE...18