181
FXUS65 KPSR 052334
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
434 PM MST Tue Aug 5 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 over the next few days.

- Moisture increases closer to seasonal averages by the end of
  the week, allowing for better daily chances for showers and
  storms, though still mostly focused over Eastern Arizona high
  terrain and Southeastern Arizona.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...
It is apparent in visible satellite imagery that some amount of
moisture has returned to the state, with cumulus fields developing
and streaming eastward off the Rim, the White Mtns, and prominent
terrain features of Southeastern AZ early this afternoon. Some
isolated weak storms or showers may be able to form with this
development, but these should remain outside the forecast area
today. Moisture is not expected to improve through Thursday, with
PWATS generally remaining below 80% of normal for the time of year
according to ensemble means, and so convective activity will
remain quite limited across the state and the CWA will stay almost
completely dry. The main story through the middle of the workweek
will be extreme heat conditions.

Current 500 mb RAP analysis places a high pressure center near El
Paso, with expansive 596+ dam heights encompassing the
southeastern 2/3 of AZ, most of NM, Western TX, and much of
Chihuahua and Sonora. Ensembles have consistently advertised this
high pressure strengthening through Wednesday, with H5 heights
peaking around 600 dam. NAEFS/EPS are in excellent agreement that
the abnormally strong high pressure will result in 850 mb
temperatures in excess of the 99th percentile of climatology. This
translates to surface temperatures capable of challenging daily
records for the time of year, particularly Wednesday and Thursday
(see Climate section). Latest NBM guidance shows fairly similar
temperatures Wednesday and Thursday, though they will likely peak
Thursday as thermal profiles take time to adjust, with lower
desert highs in a 112-117F range. Overnight lows will also not
offer much relief, with many locations only cooling into the 80s
and urban areas like central Phoenix in the lower 90s, challenging
some record warm lows. These hot temperatures mean that almost
the entire area will be under Major (level 3) HeatRisk and locally
Extreme (level 4), representing a risk to all individuals if
proper precautions are not taken. Extreme Heat Warnings expand to
cover the entire CWA by Wednesday and are in effect through the
end of the work week.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Guidance has remained in good agreement that a rather potent
trough will propagate through the northern Rockies late this week,
helping to flatten/tamp down midlevel heights associated with the
high pressure over NM, even dislodging the anticyclone further
east. Thankfully, this will bring temperatures down, with latest
NBM forecast highs falling by around 5 degrees from Thursday to
Friday. Despite this, highs remain above normal into the weekend,
and widespread Moderate to locally Major HeatRisk persist.

The positioning of the ridge will temporarily be favorable for
some southerly moist advection Friday into the weekend, however,
ensemble guidance only shows PWAT values climbing to around
90-100% of normal with values peaking around 1.3-1.4" by Saturday.
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. Day to day variations in
upstream convective activity over Sonora or Southeastern AZ could
push better low level moisture into the area to help with the
potential for lower desert storms. There are some hints in latest
GFS deterministic guidance showing a window where we could achieve
11-12 g/kg low level mixing ratios, though it remains to be seen
if we can realize the instability during these windows of better
quality moisture. As of now, Lower desert storm chances across
South-Central AZ remain very low, generally below 15%.

&&

.AVIATION...Updated at 2332Z.

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 Wednesday evening
under periods of passing high cirrus decks. Trends in winds will
be very similar to the past 24 hours with modest, occasional gusts
around 20kt during the late afternoon/early evening, and extended
periods of variability around sunrise at all terminals.

&&

.FIRE WEATHER...
Unusually hot and dry conditions will continue with temperatures trending
hotter through the middle of the week. A return of marginal
moisture over the state means that some isolated weak storms could
form over the far eastern district, presenting a threat for dry
lightning mainly on Wednesday and Thursday. 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
(outside of any distant thunderstorm outflows). Temperatures will
reach a 112-117 degree range Wednesday and Thursday for the lower
deserts, approximately 10 degrees above normal for early August,
then cool by around 5 degrees Friday but still remain above
normal through the weekend.

&&

.CLIMATE...

Record high temperatures this week:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
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>563.

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

&&

$$

SHORT TERM...Whittock
LONG TERM...Whittock
AVIATION...18/Benedict
FIRE WEATHER...Whittock/Ryan
CLIMATE...18