922
FXUS65 KPSR 280530
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1030 PM MST Thu Jun 27 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Above normal temperatures will persist through at least early next
week, with many lower desert communities experiencing high
temperatures that approach or exceed 110 degrees each afternoon.
Sunday is shaping up to be the hottest of the next 7 days, and an
Excessive Heat Watch has been issued for portions of Southeastern
California on Sunday and Monday. Drier conditions are anticipated
through Saturday across the region, with near zero rain chances on
Friday. Moisture and subsequent rain chances begin to increase again
by Sunday, likely lasting through the middle of next week.

 &&

.DISCUSSION...
Ridging still predominates over the Desert Southwest, however, the
center of the subtropical high is centered further to the south and
west than yesterday, now approximately over northern Sonora. The
feature that is bringing enhanced westerly flow aloft and our drying
trend through late tomorrow is a trough currently over the Pacific
Northwest, which will traverse the northern Rockies over the course
of the next 24 hours or so. Mid-level water vapor imagery reveals a
strong gradient in moisture across Arizona from west northwest to
the east southeast, with drier air along the base of the
aforementioned trough continuing to push into the region. Thanks to
the drier air filtering in at the mid levels, only minimal
thunderstorm/rain chances will exist for the South-Central AZ high
terrain through Saturday. Heights aloft will be somewhat suppressed
through Saturday from the influence of the trough (ensemble mean 500
mb heights maintaining values around ~589-591 dam overhead), leading
to relatively stable high temperatures ranging from around 107-112
degrees and widespread Moderate HeatRisk across the lower deserts
each day through Saturday.

Ridging will begin to build again from the east Saturday, and with
this, a return of southeasterly flow and an increase in moisture can
be expected over portions of Southern Arizona. Ensemble mean PWATs
increase from their lowest values late Friday (~1.3" over Phoenix)
back up to 1.5-1.8" over South-Central Arizona by late Sunday/early
Monday. This moisture is expected to linger through the middle of
next week, bringing daily chances for thunderstorms primarily over
the South-Central AZ high terrain (30-60%) and potentially over the
surrounding lower deserts (10-30%) Sunday through Wednesday. Global
model guidance has been fairly consistent in bringing an inverted
trough through SE AZ as early as Sunday morning. Nocturnal elevated
convection forced by this feature cannot be ruled out over portions
of SE AZ Saturday night before widespread surface- based convection
develops during the day on Sunday. DCAPE values in modeled soundings
upwards of 1500 J/kg and the mean southeasterly steering flow would
indicate an excellent environment for strong outflows to push
northwestward from the Tucson area into Pinal and Maricopa Counties
on Sunday evening, which would bring with it the potential for
widespread blowing dust. This will definitely be something to keep
an eye on going forward.

With the ridge building back from the east this weekend, confidence
in excessive heat developing continues to increase. Areas of Major
HeatRisk are anticipated across the typically hotter locations of
Southeastern California on Sunday. An Excessive Heat Watch has been
issued for locations along the Lower Colorado River Valley, portions
of East Riverside and western Imperial Counties for Sunday-Monday.
Isolated pockets of Major HeatRisk may exist over South-Central
Arizona on Sunday, however, uncertainties in cloud cover and
moisture over the area exist such that confidence in widespread
excessive heat is lower over the eastern deserts. Regardless, Sunday
is shaping up to be the hottest of the next 7 days, with forecast
highs largely ranging from 109-115 degrees across the lower deserts,
and heat safety precautions should be taken for those recreating or
working outdoors this weekend. Beyond Sunday, increased moisture and
lingering mid-high level clouds from daily convection are likely to
lead to slightly above to near normal temperatures for the eastern
deserts Monday-Thursday, though the probabilistic NBM reveals large
uncertainty for much of next week on the forecast highs. The western
deserts remain a bit hotter, with temperatures generally stable near
or slightly above 110 degrees each day after Sunday.

For the first half of next week, guidance all points toward keeping
good monsoon moisture in place across much of southern Arizona. As
the ridge center stays well to our east and another center develops
well off the coast of California, we may end up seeing some
influence from an extension of an upper level trough that sets up
over the Northern Rockies into the Great Basin. The lack of any
strong subsidence aloft in this scenario would likely result in at
least one other busy monsoon convective day at some point early next
week. Looking at the latter half of next week, ensemble guidance
generally agrees bringing in a strong ridge off the California coast
into the Great Basin area. As of now, this is expected to lead to a
period of northerly drying flow into our region around next
Thursday/Friday and hotter temperatures.

&&

.AVIATION...Updated at 0530Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No significant weather concerns will exist through Friday night with
only afternoon/evening high based cumulus over mountains and higher
terrain areas. West winds will continue well into the overnight,
however confidence is moderate that more widespread easterly winds
will develop late tonight across the metro. That said, the switch at
KPHX will be later than usual, and likely closer to sunrise. Wind
directions should quickly revert back to westerly by noon Friday
with less afternoon gustiness than experienced today.


Southeast California/Southwest Arizona including KIPL and KBLH:
A period of late afternoon/evening gusty winds will be the only
weather concern through Friday night under clear skies. Wind
directions should vary between SE and SW with the more westerly
component favored during the evening hours. Gustiness Friday will
likely be somewhat less pronounced than today, and only around 20kt.

&&

.FIRE WEATHER...
Drier conditions will continue to spread across the region from the
west through Friday, lowering humidities and essentially ending rain
chances across all areas except for far eastern Arizona. MinRHs will
lower into the teens across the majority of the lower deserts
starting today to 25-30% over higher terrain areas. Afternoon
breeziness will be common today and Friday with gusts reaching to or
just over 20 mph in many locations. The dry conditions with
virtually no chances for rain should persist through Saturday before
moisture returns Sunday, increasing humidities and potentially
bringing back chances for thunderstorms across south-central and
eastern Arizona. Temperatures through the period are expected to
average several degrees above normal.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Sunday morning through Monday evening
     for AZZ530.

CA...Excessive Heat Watch from Sunday morning through Monday evening
     for CAZ562-566-567-569-570.

&&

$$

DISCUSSION...Whittock
AVIATION...18
FIRE WEATHER...Kuhlman