850
FXUS65 KPSR 210021
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
521 PM MST Mon Jul 20 2026

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Shower and thunderstorm chances will increase today and Tuesday,
  especially over the Arizona high terrain. Isolated storms can
  also be expected into the south-central Arizona lower deserts.

- Drier conditions during the latter half of the week will greatly
  curtail monsoon storm chances with at most slight chances by
  Thursday.

- Temperatures will remain near normal early this week before
  heating up during the latter half of the week.

- Areas of Major Heat Risk are expected beginning Thursday with a
  high likelihood of fairly widespread Major to Extreme Heat Risk
  by the weekend.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
Mid-lvl WV imagery and RAP-40 500mb analysis show the subtropical
ridge expanding across most of the Desert SW and into the south-
central Plains. Easterly to southeasterly winds aloft are still
advecting decent moisture into the region, with PWATs from this
morning`s 12Z sounding 1.8". Current mesoscale analysis does show
some drying has occurred over the Metro this afternoon, however
PWATs are still hovering between 1.4-1.9" across the entire
region. Heading into this afternoon/evening ensembles are in good
agreement for storm development in the eastern high terrain with
MUCAPEs forecasted between 500-1000 J/kg and mixing ratios
remaining between 11-13 g/kg. Where the agreement falls apart in
the models is whether any additional storms will be able to
develop into the lower deserts as outflows push through. The
latest HRRR is more optimistic for lower desert redevelopment,
while other HREF members show very limited potential. Even with
this uncertainty PoPs for the Phoenix Metro will remain between
20-30% while the eastern higher terrain will be between 50-70%.
Otherwise, gusty winds up to around 35 mph and localized heavy
rainfall will be the main weather concerns for the AZ higher
terrain tonight. While gusty winds and patchy blowing dust will be
the main concerns over the lower deserts with HREF members
showing a 30-50% (mostly near 30%) chance of wind speeds above 35
mph this evening, however similar to PoPs, the HRRR is very
optimistic of an outflow from the higher terrain moving through
with speeds near 35-40 mph.

Similarly to the past few mornings lingering showers and a few
storms will remain possible across south-central and eastern
Arizona into Tuesday morning as the inverted trough moves into
western New Mexico. Tuesday afternoon/evening is expected to be
similar to today with HREF members again in great agreement of
thunderstorm development in the eastern high terrain. This will
bring localized heavy rainfall, with WPC putting a more expansive
slight risk for excessive rainfall over eastern Arizona, with
localized areas in Gila County may receive upwards of 1-2 inches
of rainfall an hour. Due to this a Flash Flood Watch has been
issued starting Tuesday afternoon through Tuesday evening for
Eastern Gila County, when the peak rainfall is expected to occur.
Otherwise, southerly drying flow into the lower deserts is likely
to further inhibit chances in the Phoenix area, with even the
HRRR showing limited chances of storm development.

Heat impacts early this week should be fairly limited with Minor
to Moderate HeatRisk through Tuesday. Forecast highs are still
below normal across central and eastern Arizona, but for southwest
Arizona and southeast California highs will begin to push to above
normal as early as Tuesday. Overnight temperatures are expected
to fall within the normal range with lows in the low to mid 80s
across the lower deserts.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Model guidance is now trending toward a noticeably less active
monsoon period during the latter half of the week, largely in part
due to the subtropical high strengthening and setting up over
west Texas through our region. The main forecast concern will
quickly shift from monsoon storms to extreme heat by Thursday.
Ensembles show the high shifting southward starting Wednesday and
then expanding into our region Thursday into Friday as H5 heights
over our region quickly rise from 591-593dm Wednesday to
596-598dm by Friday. Southerly dry flow will pick up across our
area on Wednesday, decreasing rain chances further before chances
likely drop below 10-15% starting Thursday as strong subsidence
spreads over the region.

Temperatures should quickly respond to the increasing heights and
the decreasing monsoon activity later this week. NBM forecast
highs show readings topping 110 degrees as early as Wednesday
across southeast California and as early as Thursday across the
Arizona lower deserts. Areas of Major HeatRisk are expected by
Thursday, likely expanding in coverage Friday into the weekend as
the heat reaches its peak. Overnight lows will also become an
issue as surface moisture remains elevated enough to cause lows to
only dip into the upper 80s to lower 90s by Thursday. Daytime
highs of 113-116 degrees across the western deserts to 110-113
degrees in the Phoenix area are shown for this weekend, while heat
indices of 115 degrees are likely to appear as early as Thursday
for the western deserts. Due to this an Extreme Heat Watch has
been issued for Southeast California Starting Wednesday and then
expanding eastwards to include south central Arizona and the
Phoenix Metro starting Thursday.

&&

.AVIATION...Updated at 0020Z.

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

There is high confidence one or more outflow boundaries, will move
through the terminals this evening, with the most favorable
direction being from the NE after 02-03Z. There is notably lower
confidence in storms surviving into the metro area with the
outflow, given the late afternoon environment was not conducive.
At least VCSH/-SHRA from decaying activity or debris showers may
still develop/progress into the metro this evening. W/SW winds
around 10 kts will prevail ahead of NE/E outflow winds. Outflow
winds may briefly gust to 25-30 kt to as high as 35-40 kt (10-20%
chance). Following the outflow, winds are expected to remain
easterly through Tuesday morning, but any rain activity in the
metro may create erratic winds. W/SW winds will develop again
Tuesday afternoon at all terminals with speeds around 5-10 kt. FEW
to BKN clouds, with lowest bases down to 8-10K ft AGL will be
common.

Southeast California/Southwest Arizona including KIPL and KBLH:

No significant aviation weather concerns are expected through the
next 24 hours. Winds at KIPL will favor a W component this
evening through tonight, with a period of gusts as high as 20-25
kts late this evening. At KBLH, winds will predominantly favor a
S to SW component through the period. Expect elevated wind speeds
this afternoon/evening around 8-12 kts and a few gusts to around
20 kts. Can`t rule out isolated VCSH at the terminals Tuesday
morning through the afternoon, however, chances of this occurring
are 10% or less. FEW to SCT clouds aoa 10 kft will be common
throughout the period.

&&

.FIRE WEATHER...
Ample moisture will be available for additional rounds of showers
and storms through at least Tuesday for the Arizona higher
terrain. Much more limited chances are expected over the Arizona
lower deserts. Humidities will remain elevated with MinRHs mostly
ranging from 20-25% across the western districts to 25-40% across
the eastern districts, while overnight recoveries remain good.
Outside any influences from showers and thunderstorms, winds early
this week will tend to favor the southwest with only short
periods of downslope easterlies late at night for the eastern
districts. Hotter temperatures with some slight drying is
expected during the latter half of the week as a stronger high
pressure system sets up over the region. Rain chances will be
greatly diminished by Thursday, likely lasting through the
upcoming weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Watch from Wednesday morning through Monday evening
     for AZZ530-532.

     Flood Watch from Tuesday morning through Tuesday evening for
     AZZ556-560-562-563.

     Extreme Heat Watch from Thursday morning through Monday evening
     for AZZ531-533>555-559.

CA...Extreme Heat Watch from Wednesday morning through Monday evening
     for CAZ562>570.

     Extreme Heat Watch from Thursday morning through Monday evening
     for CAZ560-561.

&&

$$

SHORT TERM...Ryan/Kuhlman
LONG TERM...Ryan/Kuhlman
AVIATION...Benedict/Smith
FIRE WEATHER...Kuhlman