862
FXUS65 KPSR 280000
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
500 PM MST Fri Jun 27 2025

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Temperatures will heat up through the weekend with widespread
  Moderate HeatRisk developing across all areas by Sunday and
  lower desert high temperatures topping out between 110 and 115
  degrees for Sunday through Tuesday

- An Extreme Heat Warning has been issued for the Phoenix metro
  Sunday through Tuesday with the rest of Maricopa and Pinal
  Counties issued only for Monday as areas of Major HeatRisk
  develop.

- Dry conditions will prevail through at least the weekend, but a
  gradual increase in moisture next week is likely to lead to
  increasing chances for showers and thunderstorms for portions of
  Arizona as early as the middle part of next week

&&

.DISCUSSION...
Persistence forecast continues for today, as dry southwesterly
flow continues with daily shower and storm activity in far
southeastern Arizona. The enhanced moisture axis east of the
region will degrade going into and through the weekend as drier
air filters in as persistent troughing deepens once again offshore
of the California coast that`ll enhance dry southwesterly flow
aloft in concert with subtropical ridging building in from the
east into the region. This combination will keep dry conditions
into early next week, with temperatures rising back above normal
this weekend.

Widespread Moderate HeatRisk will develop across the region by
Sunday, with areas of Major HeatRisk peaking on Monday. Extreme
Heat Warnings are in effect Sunday-Tuesday for the Phoenix metro
and other areas of northwestern Pinal and Maricopa Counties for
Monday only. Highs in central Phoenix may reach record territory
on Monday as the hottest day of this three day period is currently
forecasted at 115 degrees, which would tie the record high for
that date back in 1979 and 2013 (~75% chance of tying, ~40% of
breaking). Warmer overnight temperatures are also contributing to
the Warnings lasting through Tuesday as the rise into the mid to
upper 80s late this weekend/early next week (30-50% chance
overnight lows remain 90 degrees or above for central Phoenix
Monday night). These elevated lows are in part due to increasing
moisture levels due to an expected pattern change beginning on
Monday.

The aforementioned troughing feature will meander eastward early
next week, pushing the subtropical high center east of the region.
This eastward movement will cause temperatures to cool starting
Tuesday, but more importantly begin the influx of moisture as the
high sets up somewhere around the Four Corners region by the
middle of the week. Ensembles spread continues to hamper honing in
on better timing and outlook heading into the middle of next week,
as the GEFS continues to remain bullish on higher PWAT anomalies
building into eastern to central Arizona quicker than the ECMWF
starting on Monday, whereas the ECMWF remains more delayed into
Tuesday. These differences would dictate which day the onset of
more robust convection may begin to develop starting in
easter/southeastern Arizona, and eventually into the region, even
for the lower deserts later in the week. Despite these
differences, with this transition will pose a day or two of dry
lightning threats, along with outflows propagating from more
robust convection in the higher terrain areas and southeastern
Arizona that could lead to gusty outflow winds and a blowing dust
threat for lower desert areas of south-central Arizona.

Once the better moisture builds to around 100-150% of PWAT normals
by the middle of next week, higher terrain showers/storms seems
more likely to maintain convection to the lower deserts, even into
Phoenix, most realistically starting Thursday (at the earliest).
The ECMWF has higher wet PWAT anomalies for Wednesday and Thursday
than previous runs across Arizona, so this change would bode well
for lower desert convection chances late next week if this trend
continues. Bottom line is model guidance needs to come into better
agreement before we can start nailing down the daily shower/storm
chances with more certainty. At the very least, it is certain
that the pattern will transition into a brief period of a
monsoonal pattern, with the trough offshore of the West Coast
limiting the robustness of the moisture and how long this moisture
will linger into late next week due to the dry southwesterly flow
aloft. As mentioned previously, it doesn`t look like the tropical
system tracking northwestward from the subtropics will provide
any assistance to the moisture levels late next week, thus how the
subtropical high sets up will dictate the shower/thunderstorm
potential next week. With that said, NBM PoP`s continue to run
high due to biases related to coming out of a dry period, thus
some changes were made to accommodate that.

&&

.PREVIOUS DISCUSSION...
Beyond next Friday (July 4th), both the GEFS and EPS generally
favor a return of dry southwesterly flow through all of the Desert
Southwest, mostly due to that near persistent trough
restrengthening just to our west.

&&

.AVIATION...Updated at 0000Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Winds will continue to follow diurnal trends through Saturday,
with prevailing clear skies. Wind speeds up to 8-12 kts are
expected to continue through the next couple hours and return
again tomorrow afternoon and evening, with gusts up to 15-20 kts.
Speeds will subside late this evening and remain light through
tomorrow morning. Diurnal easterly winds will develop by 8-12Z
tomorrow morning and turn back westerly by 16-17Z tomorrow.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will come around to the west by 00-01Z at KIPL this evening,
with speeds increasing up to 10-14 kts for a few hours. Wind
directions then return to a southeasterly component by 14-15Z
tomorrow morning. Winds will maintain a southerly component at
KBLH for most of the TAF period, with gusts to around 20 kts this
evening and again tomorrow afternoon and evening. Lofted
smoke/haze may at times lower slantwise visibility during the
late afternoon/evening hours.

&&

.FIRE WEATHER...
High pressure will gradually strengthen across the region through
the weekend leading to a strong warming trend and continued dry
conditions. Temperatures will warm to several degrees above
normal starting Saturday before peaking early next week. Expect
little change in humidity trends as MinRH values continue to range
between 5-15% each day and overnight recoveries stay between
20-35%. Winds will follow familiar diurnal trends with typical
afternoon breeziness, gusting mainly between 15-20 mph.
Eventually, the weather pattern should become more favorable for
increasing moisture and at least some scattered high terrain
showers and thunderstorms by around next Tuesday. This may
initially result a day or two of dry lightning concerns before
moisture and rainfall chances increases later next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning from 10 AM Sunday to 8 PM MST Tuesday for
     AZZ537-540-542>544-546-548-550-551.

     Extreme Heat Warning from 10 AM to 8 PM MST Monday for AZZ534-
     538-539-541-545-547-549-552>555-559-560.

CA...None.
&&

$$

DISCUSSION...Young
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Benedict
FIRE WEATHER...Young/Kuhlman