251
FXUS65 KPSR 220018
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
518 PM MST Mon Jul 21 2025

.UPDATE...Updated 00z Aviation Discussion.

&&

.KEY MESSAGES...

- Below normal temperatures early this week will gradually warm
  closer to the seasonal average by the end of the week resulting
  in widespread minor HeatRisk increasing to a moderate level.

- Chances for showers and thunderstorms will linger through the
  first half of the week with the better chances focused over the
  Arizona high terrain before drier air sweeps into the region
  midweek.


&&

.SHORT TERM /Today through Tuesday/...
Morning showers and mid-level clouds have mostly cleared out early
this afternoon. Widely scattered storms developed quickly today
across northern Sonora and southeast AZ, but drops off quickly
into South-Central AZ. Mesoanalysis at 1 PM MST shows MUCAPE in
excess of 500 J/kg across much of southeastern AZ that drops off
to <100 J/kg in Phoenix. This lack of instability is not favorable
for additional rain chances this afternoon. Plus, BL moisture is
still sub-optimal, with surface dew points in mid-40s to low-50s
and mean mixing ratios around 8-9 g/kg. It is not impossible for a
convective shower or storm to move up from the south and tease
into parts of Phoenix this afternoon and evening, especially with
any moist outflow boundary, but nearly all activity today should
stay south of Phoenix. Areas from Gila Bend through northwest
Pinal county and into southern Gila county, will stand the best
odds (>20%) for showers and storms this afternoon. Biggest impacts
this afternoon will be some brief heavy downpours and strong
gusty outflow winds, which may kick up localized dust in the I-8 &
I-10 corridors. There remains a sharp drop off in moisture west
of Maricopa County and this delineation will persist through
tomorrow. So, rain chances are zero for nearly all areas west of
this line.

Heading into Tuesday there is still a lot of uncertainty around
timing, location, and intensity of any shower and storm activity.
However, the environment will become much more favorable for rain
across South-Central AZ. A notable increase in moisture is
expected from the south and southeast tonight, likely emanating
from the widely scattered activity to the southeast this
afternoon. Global and hi-res models show PWATs increase up to
1.6-1.8" and surface dew points climb into the low to mid 60s
along with low level mixing ratios increasing up to around 12
g/kg. With this BL moistening, instability will also go up, to
better support more robust updrafts. Synoptic forcing will also
become a little better with increasing jet energy ahead of the
deepening trough in the northwest CONUS.

The question is how will this uptrend in conditions translate to
actual wetting rain on the ground, amongst other potential
impacts. Models are still indicating a few different scenarios for
tomorrow including a perhaps a similar outcome to today with best
rain chances in the Phoenix area during the morning and then
storms focus south to east of Phoenix in the afternoon. Latest NBM
supports this outcome with 20-40% PoPs in the Phoenix area in the
morning and then 20-40% PoPs in the afternoon south, east, and
north of Phoenix. A less active morning, with mainly just
extensive cloud cover again that clears heading into the
afternoon, could bode well for better storm chances in the
afternoon. If MLCAPE values up to 1000 J/kg can be realized
tomorrow afternoon through surface heating, more robust and
impactful storms will be capable of developing with potential for
strong gusty winds and at least locally minor flooding impacts.
For what it is worth, the majority of global ensemble members have
measurable rain in Phoenix tomorrow morning and a few hi-res
models also mostly support morning convection. To piggyback on the
rain chances tomorrow, high temperatures may not reach 100
degrees in Phoenix. Anytime this is the case in Phoenix in July it
is a sign that there may be rain impacts during the day or at
least thick clouds that inhibit heating.

&&

.LONG TERM /Wednesday through Sunday/...
Ensemble membership remains in excellent agreement advertising an
expansive subtropical anti-cyclone sprawling across the SE Conus
while deep negative height anomalies become established along the
California coast with strong SW flow impinging into the forecast
area. With H5 heights barely eclipsing 590dm, temperatures will
continue to hover below the daily normals during the middle of the
week with only modest warming towards the end of the week as
subtropical ridging slowly begins to retrograde incurring minor
height rises by the weekend. The aforementioned SW flow will
continue to strengthen helping rapidly erode moisture across the
region during the latter half of the week. Latest GFS BUFR soundings
suggest mixing ratios falling below 5 g/kg and total column PWATs
near 0.50" by Wednesday afternoon essentially precluding
thunderstorm development outside of mountain locations. Widespread
dry weather seems an almost certainty during the end of the week,
and it will take the reestablishment of strengthening high pressure
over the four corners early next week to resume deep SE flow and
start the whole monsoon flow process and convective progression
over.

&&

.AVIATION...Updated at 0020Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Winds continue to be erratic in directions and speeds late this
afternoon, resulting in the biggest aviation challenge in the
short term. Showers to the south of all terminals warrant VCSH
conditions through this evening, although no real threat is
anticipated to approach into the 10 mile range. An outflow from
the south looks to reinforce southerly gusty winds with some
reductions in visibilities possible over the next couple of
hours, hence a TEMPO for westerly winds at KPHX through this
evening. BKN to OVC skies will persist into tonight, with another
round of VCSH conditions during the overnight hours and into
tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the next
24 hours under mostly clear skies. Winds will otherwise continue
to predominantly favor the E-SE at KIPL with a shift to the
southwest for a period this afternoon and evening. KBLH, general
southerly winds with some afternoon and early evening gusts to
around 20 kts.

&&

.FIRE WEATHER...
A warming and drying trend will predominate the region this week as
temperatures several degrees below the daily normals return closer
to the seasonal average by the end of the week. The chance for
showers over eastern districts the next couple days will retreat
into higher terrain areas midweek, then eventually outside of the
forecast area by the latter half of the week. Even with a few
showers the next couple days, wetting rainfall chances are quite
low. Otherwise, minimum afternoon humidity values in a 15-30%
range will fall into a 5-10% range during the second half of the
week. Similarly, fair to good overnight recovery of 30-70% will
decrease into a poor to fair range of 20-40% late in the week.
Winds should be fairly typical through the week with only the
typical afternoon upslope gustiness.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

SHORT TERM...Benedict
LONG TERM...18
AVIATION...Young/Frieders
FIRE WEATHER...18