451
FXUS65 KPSR 210518
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1018 PM MST Thu Aug 20 2026

.UPDATE...Updated 06z Aviation Discussion...

&&

.KEY MESSAGES...

- After a brief reprieve from the extreme heat today over south-
  central and eastern Arizona, highs will return to around 110
  degrees by Friday, lasting into early next week.

- Extreme Heat Warnings are in effect through Sunday evening due to
  continued areas of high-end moderate to major HeatRisk.

- Isolated thunderstorms are expected across the AZ high terrain
  this afternoon and evening with less than 10% chances for the
  lower deserts. Chances will likely remain confined to the high
  terrain through at least Saturday.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...
After the biggest monsoon event of the season so far in the
Phoenix Metro area, we are not anticipating much if any activity
in the lower deserts today due to an overturned atmosphere. Latest
visible satellite and composite radar imagery reveals a remnant
MCV left over from last night`s storm complex which is now
progressing through the Yuma area. This MCV is expected to
continue bringing an area of light to moderate showers with a few
embedded lightning strikes to Yuma and Imperial Counties over the
next few hours before finally dissipating. Farther east, skies
have cleared out across southcentral AZ allowing temperatures to
begin rising, however highs in the Phoenix area will likely top
out right around normal due to residual moisture from previous
rainfall. Therefore, NBM high temperatures were adjusted down by
several degrees this afternoon and overnight lows tonight as well.
Latest RAP 13 mesoanalysis across southcentral AZ shows CAPE
values are still around 1000-1200 J/kg, but there is a much
stronger mid-lvl inversion today with ML CIN on the order -120
to -150 J/kg. Therefore storm coverage will be much more isolated
this afternoon, and without a strong outflow, little to no storms
are expected across the lower deserts this afternoon and evening.

Deterministic models and ensemble members suggest the subtropical
high will shift over Colorado on Friday and then migrate into
eastern NM on Saturday. This shift in the upper-lvl pattern will
cause winds to turn more out of the south, ushering drier air into
our beginning on Friday. Both the GEFS and ECS show PWATs falling
to 1.3" or lower and mixing ratios as low as 7-8 g/kg. As such,
NBM PoPs for both Friday and Saturday fall below 10% for the lower
deserts to 10-20% over portions of the high terrain. Despite
storm coverage decreasing substantially, there will still be a
chance of a distant outflow from storms along the International
Border reaching Maricopa or Pinal Counties, but additional storm
development is unlikely. Although the ridge axis will shift ewd
into this weekend, overall 500 mb hght fields will remain largely
unchanged from previous days. Therefore, we should see a return of
above normal temperatures and extreme heat conditions by Friday
and persisting into this weekend and the Extreme Heat Warning will
remain in effect through Sunday.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Model uncertainty remains quite high for the first half of next
week as the position of the high is likely to set up somewhere
over eastern New Mexico and western Texas by Monday with little to
no movement into the middle of next week. This position can cause
higher uncertainty in moisture levels for our area with the
latest guidance trying to advect some moisture into our area by
Sunday or Monday, but NBM forecast PoPs are at most 10-15% for the
lower deserts. At this point, we could continue to see mostly
slight chances favoring the high terrain into early next week, but
if moisture does eventually improve enough storm chances are
likely to be higher than what the NBM is depicting. Another
wildcard will be the potential influence of an upper level trough
that may attempt to move into western portions of our region
Sunday into Monday. If this occurs, it may be enough to improve
convective potential across southeast California and western
Arizona for Sunday and/or Monday.

Temperatures are expected to continue to be more influenced by the
strong subtropical high as H5 heights hover between 593-596dm
across the Desert Southwest through early next week. Daytime highs
are not expected to change much day to day from Sunday through
early next, barring any significant change with the convective
chances. The Extreme Heat Warning is currently in effect through
Sunday, but it seems quite likely it will need to be extended
again at some point.

&&

.AVIATION...Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected throughout the TAF
period under FEW-SCT mid/high cloud decks. The overall wind
pattern will follow the typical diurnal tendencies with overall
speeds remaining aob 10 kts. Wind directions do become a bit more
uncertain Friday evening as there are some indications from the
hi-res guidance that storm activity across southeast AZ may send
a decaying outflow boundary into the area, with a potential wind
shift out of the south-southwest to south. However, at this time,
no significant gusts are anticipated if the outflow comes to
fruition.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected throughout the TAF
period under FEW-SCT mid/high cloud decks. Winds will generally
fluctuate out of the southeast to southwest direction with speeds
under 12 kts. Periods of light variability will be common during
the early morning hours.

&&

.FIRE WEATHER...
Elevated moisture levels will persist today with a temporary
reprieve from the extreme heat across much of the area. Expect
mainly isolated showers and thunderstorms this afternoon and
early evening over the AZ high terrain, with a less than 10%
chance of storms in the lower deserts. Drier air will filter into
the region Friday and Saturday with even lower chances for rain
while temperatures heat back up to extreme levels. MinRHs of
20-30% today will lower to 15-25% beginning Friday. Winds should
overall follow the typical diurnal tendencies with some modest
afternoon upslope gustiness.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530>544-546-
     548>551-553>555-559-560.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ562-565>567-
     569-570.

&&

$$

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