517
FXUS65 KPSR 111129
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
429 AM MST Mon Aug 11 2025

.UPDATE...Updated Aviation Discussion...

&&

.KEY MESSAGES...

- Above normal highs and warm overnight lows will continue to
  yield widespread Moderate to localized Major HeatRisk early
  this week.

- Major HeatRisk will be concentrated particularly over the
  central AZ lower deserts, the Lower Colorado River Valley, and
  Imperial Valley where Extreme Heat Warnings remain in effect
  through Tuesday evening.

- Isolated to widely scattered showers and thunderstorms will be
  possible across the higher terrain of southcentral AZ through
  mid-week.

- Increasing moisture late week will result in better coverage of
  thunderstorm activity across much of the region including the
  lower deserts.

&&

.SHORT TERM /Today through Tuesday/...
Current mid-lvl wv imagery and 500 mb streamline analysis reveals
an elongated ridge of high pressure centered over N California as
a broad trough of low pressure is progressing through the upper
Midwest. Our forecast area is located between both of these
features but will remain under the influence of ridging through at
least the first half of this week. Due to the ridge positioning
to our NW, mid-lvl flow will be more N-NE over the next few days
resulting in mostly dry conditions for the lower deserts of
southcentral AZ. As moisture remains limited, expect only isolated
coverage of showers and thunderstorms across the high terrain
areas mainly E and NE of Phoenix through Tuesday. Chances for any
distant outflows reaching the lower deserts will also be low
around 10-30%. Hghts aloft will remain between 592-594 dam today
and Tuesday which will result in lower desert highs ranging
between 108-115 degrees. Temperatures of this magnitude combined
with warm overnight lows will continue to foster widespread
Moderate to locally Major HeatRisk. Therefore an Extreme Heat
Warning remains in effect for the lowest elevations of
southcentral AZ and southeast CA through Tuesday evening.

&&

.LONG TERM /Wednesday through Sunday/...
Beginning on Wednesday, ensemble guidance continues to indicate a
trough of low pressure entering the Pacific Northwest while the
subtropical high centered over the Great Basin begins to weaken and
shifts eastward toward the Four Corners area. This shift in location
of the high will establish NE mid-lvl flow over the forecast area
and potentially bring any storms that form over the Mogollon Rim
into the lower deserts. The main limiting factor will be moisture
availability with PWATs only rising to around 1.2-1.3" by Wednesday
afternoon. Right now NBM PoPs are around 30-40% across the high
terrain and up to 20% for the lower deserts Wednesday afternoon
and evening. As hghts aloft begin to decrease on Wednesday, high
temperatures will cool by a degree or two, however many lower
desert communities including Phoenix, Yuma, and El Centro are
still forecast to reach the 110 degree mark.

Heading through the latter half of this week and into this weekend,
ensemble and deterministic model guidance continue to indicate
the aforementioned trough of low pressure over the Pacific NW will
become more amplified off the coast of CA while the subtropical
high migrates into the Southern Plains. As this occurs, there will
be a better opportunity for deeper moisture to be pulled into
southern AZ. However, it is important to note that there is still
quite a bit of disagreement between the EPS and GEFS regarding the
magnitude of moisture return. The EPS is continuing to indicate
better moisture return with PWATs rising to around 1.5-1.6" on
Thursday and Friday, whereas the GEFS is only showing PWAT values
maxing out around 1.3-1.4". This discrepancy is likely due to the
strength and positing of the trough to our west. Despite these
differences, NBM PoPs have not changed much and are still hovering
around 30-40% across the lower deserts and up to 50-60% across
the high terrain of southcentral AZ both Thursday and Friday. Due
to the presence of the trough and uptick in moisture, temperatures
will decrease to near normal with highs topping out around
100-107 degrees across the lower deserts Thursday and Friday.

By this weekend, drier air associated with troughing to our west
will begin to overspread our region, resulting in much more
limited thunderstorm activity across the state. Although we will
see a drying trend, the troughing pattern over the western U.S.
will help keep 500 mb hghts suppressed and thus we will continue
to see temperatures near seasonal norms through Sunday.

&&

.AVIATION...Updated at 1130Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Little to no aviation impacts expected today as any rain chances
will remain over far eastern Arizona. West winds will dominate
through at least midnight with a period of breeziness with gusts
upwards of 20 kts late afternoon/early evening. Skies will remain
mostly clear the bulk of the period with any clouds at or above
15K feet.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are expected over the next 24 hours
under generally clear skies. Winds at KIPL will generally remain
out of the east-southeast through Monday evening, while KBLH will
continue to see more southerly winds.

&&

.FIRE WEATHER...
Above normal temperatures will continue through the middle of this
week but increasing moisture will result in a cool down to near
normal temperatures by the end of the week. Chances of wetting
rainfall will remain below 10% through Tuesday, resulting in
potential for dry lightning and new fire starts. During the
Wednesday through Friday time period, the CWR will increase to
around 20-30% across the AZ high terrain. Minimum afternoon
humidity levels will mostly range between 15-20% each afternoon with
fair to good overnight recovery anticipated. Winds will continue
to follow normal diurnal patterns (afternoon upslope followed by
downvalley overnight) with afternoon gusts to 15-20 mph common.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Tuesday for AZZ530-532-534-
     537>544-546-548>551-553>555-559.

CA...Extreme Heat Warning until 8 PM PDT Tuesday for CAZ562-563-566-
     567-569-570.

&&

$$

SHORT TERM...Salerno
LONG TERM...Salerno
AVIATION...Kuhlman
FIRE WEATHER...Salerno