Flash Flood Warning 28, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
500 PM MST Sun Aug 9 2026

.UPDATE...00Z Aviation Discussion

&&

.KEY MESSAGES...

- Extreme Heat Warnings remain in effect for much of the region
  through this evening and portions of the Lower Colorado River
  valley and Imperial Valley on Monday due to widespread moderate
  to locally Major HeatRisk.

- Shower and thunderstorm activity will once again develop across
  the higher terrain of southcentral and southeast Arizona later
  this afternoon, which will bring strong outflows into the lower
  deserts and potentially result in additional storms this evening.

- Deeper moisture will provide a better opportunity for more widespread
  shower and thunderstorm activity during the first half of this
  week, along with noticeably cooler temperatures.

&&

.SHORT TERM /Today through Monday/...
Latest GOES mid-lvl visible satellite imagery reveals mostly clear
skies over southcentral AZ with pockets of cu beginning to percolate
over the higher terrain areas including the White Mountains,
Mogollon Rim, and mountains of southeast AZ. Large anti-cyclonic
flow is apparent over the 4-Corner region where high pressure is
currently situated. Similar to the past several days, storms are
expected to develop over the high terrain this afternoon and attempt
to descend into the lower deserts this evening. Atmospheric
conditions for additional storm development are still not optimal
as indicated by a large area of ML CIN (-80 to -100 J/kg) over
Maricopa County. However, there is also much higher DCAPE present
(up to 1900 J/kg noted on the 12Z KPHX RAOB). This could promote a
stronger and longer lived outflow boundary this evening which is
likely to sweep across Maricopa and Pinal County and could produce
isolated to widely scattered convection in its wake. The main
concerns with any thunderstorm related outflow will be gusty
winds up to 30-40 mph along with areas of blowing dust, especially
in the most dust prone areas of northern Pinal and western
Maricopa County. Due to the higher DCAPE values, any storm that
develops across the lower deserts could also produce marginally
severe wind gusts up to 60 mph. Storm activity should wane by
midnight with much calmer conditions anticipated overnight.

Environmental conditions for thunderstorm activity on Monday will
drastically improve across our forecast area. The subtropical high
will remain positioned near the Four Corners Region, with the
addition of increasing mid-lvl flow around 30 kts. Moisture
advection will also improve with PWAT values increasing to 1.5-1.8"
along with low-level mixing ratios exceeding 11 g/kg. This will
allow for higher instability and weaker convective inhibition across
the lower deserts. Short-term models also indicate an increase in
upper-level divergence as a weak easterly wave moves into northern
Mexico, which will likely aid in higher thunderstorm coverage,
especially across southeastern AZ. High-res guidance does show
multiple outflow converging somewhere in Maricopa County by Monday
evening/Monday night which would result in additional storm
development. Strong downburst wind gusts, locally heavy rainfall, as
well as areas of blowing dust in the typical dust prone areas will
all be likely. NBM PoPS are still hovering around 40-50% across much
of southcentral AZ on Monday night (mainly after 00Z) which are some
of the better chances we have seen for the monsoon season thus far.

The unseasonably strong subtropical ridge over the 4-corners will
continue to promote above normal temperatures through Monday, with
afternoon highs peaking around 108-112 degrees this afternoon,
resulting in areas of Major HeatRisk. Thus, an Extreme Heat Warning
remains in effect for a majority of the forecast area through this
evening. Heading into Monday, lowering heights/thickness will allow
further cooling, although afternoon highs will still remain a few
degrees above the daily normal. Overall, HeatRisk will fall to the
Moderate category on Monday afternoon, however heat index values
will still be very high (up to 115-118 degrees) across portions of
southeast CA and the Lower Colorado River Valley. Therefore, a
continuation of the Extreme Heat Warning was made for some areas
along and west of the Colorado River including Yuma, the Imperial
Valley, and Salton sea through Monday evening.

&&

.LONG TERM /Tuesday through Saturday/...
Conditions will remain favorable through the middle of the week
for additional monsoonal activity. Depending on how active Monday
turns out, Tuesday could actually be more of a down day given a
worked over atmosphere and thus even though there is still
potential for storm activity, especially across the higher terrain
areas, NBM PoPs for Tuesday are lower, mostly ranging between
30-50%. Another more active period appears to be in the cards for
late Wednesday into the first half of Thursday. The flow by
Wednesday is forecast to shift out of the south as the subtropical
high shifts into Texas and a upper-level low moves off the coast
of California. This southerly flow is likely to bring additional
moisture northward from Mexico, with projected PWATs increasing to
1.7-2.0" and low-level mixing ratios increasing to 12-13 g/kg. In
addition, there will likely more favorable upper-level forcing as
both the GFS and ECMWF do indicate an upper-level wave moving
into the region from Mexico, which will likely enhance the
convective activity with flash flooding becoming more of a threat
given the deeper moisture profiles that will be in place. The
latest NBM PoPs for late Wednesday through the first part of
Thursday currently range between 50-60% across much of south-
central and southeast AZ.

Heading towards the end of the week and next weekend, the guidance
is in good agreement in showing the subtropical high shifting
towards the Gulf Coast Region while the aforementioned upper-
level low remains situated off the west coast. This pattern
configuration will cause the flow to shift more out of the
southwest, bringing in drier air as PWATs drop under 1.2-1.3". As
a result, an overall downtrend in storm activity is likely.

With the lowering heights aloft and as well as an increase in
convective activity and cloud cover, temperatures throughout the
upcoming work week are expected to gradually cool with afternoon
highs expected to fall to near seasonal levels by Tuesday and
potentially a few degrees below normal by the latter half of the
week. Temperatures do eventually trend slightly back up again by
next weekend, but to near seasonal levels with no extreme heat in
sight.

&&

.AVIATION...Updated at 0000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary aviation concerns this evening will be strong outflow
winds, blowing dust, and isolated thunderstorm activity.
Confidence is moderate that at least one outflow boundary will
move through the Phoenix metro from the south, with the most likely
arrival time favored between the 01-02Z timeframe. This boundary
will be capable of producing sudden wind shifts with gusts up to
20-30kts, and a 50% chance for peak gust to exceed 30-35kts. These
strong winds will likely generate blowing dust, which could
result in localized visibility reductions at the terminals. While
thunderstorms may accompany or trail the outflow, confidence in
direct impacts at the terminals remains low (around 20% chance),
so PROB30 groups continue to cover this threat. Cloud bases with
any convection are expected to be around 10 kft, with SCT-BKN mid
to high level clouds otherwise persisting. Prior to the arrival of
outflows, winds will remain generally light (aob 10 kts) favoring
a westerly component. In the wake of the evening outflows, wind
directions will carry a high degree of uncertainty but are
expected to eventually settle out of the south to southeast late
this evening and into the overnight hours. A typical diurnal shift
back to the west is anticipated Monday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the next
24 hours under periods of FEW-SCT mid to high cloud decks and
otherwise mostly clear skies. At KIPL, winds will primarily stay
southeasterly. At KBLH, winds will generally fluctuate between SE
and SSW. Overall, wind speeds should generally remain AOB 12 kts.
A distant thunderstorm outflow reaching KBLH this evening cannot
be ruled out, which would result in an abrupt wind shift and
potentially some VIS restrictions due to lofted/blowing dust.

&&

.FIRE WEATHER...
Above normal temperatures with afternoon highs reaching 108-112
degrees can be expected across the lower deserts today, before
gradual cooling to more seasonal levels takes place during the
upcoming week. Elevated moisture will maintain afternoon MinRHs
above 20% each afternoon along with good to excellent overnight
recoveries. Shower and thunderstorm activity will again remain
isolated today and tonight, but coverage is expected to become more
widespread in through the first half of the week. The chances of
wetting rainfall will also increase significantly, especially across
the eastern districts. Outside of gusty and erratic winds due to
thunderstorms, winds will follow the familiar diurnal trends, with
typical afternoon upslope breeziness around 20 mph.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Monday for AZZ530-532.

     Extreme Heat Warning until 8 PM MST this evening for AZZ531-
     533>544-546-548>551-553>555-559.

CA...Extreme Heat Warning until 8 PM PDT Monday for CAZ563-566-567-
     569-570.

     Extreme Heat Warning until 8 PM PDT this evening for CAZ560>562-
     564-565-568.

&&

SHORT TERM...Salerno
LONG TERM...Lojero
AVIATION...95/Ryan
FIRE WEATHER...Lojero/Salerno

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