554
FXUS65 KPSR 272143
AFDPSR

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

.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 1750Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns expected through the TAF
period. Winds through the evening and at least through the first
part of the overnight period will be out of the west with
sustained speeds aob 12 kts. Gusts this afternoon through early
this evening could occasionally peak at 20-25 kts before subsiding
later in the evening and overnight. Winds early Friday morning
will likely be light and variable to briefly switching out of the
east before switching back out of the west by the mid to late
morning hours. FEW to occasionally SCT mid to high-level clouds
expected through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns under mostly clear skies expected
through the TAF period. At KIPL, winds will be out of the
southeast through this afternoon before switching out of the west
this evening. At KBLH, winds are expected to fluctuate between
the south to southwest. Wind gusts this afternoon through this
evening in excess of 20 kts will be common at both sites.

&&

.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...Lojero
FIRE WEATHER...Kuhlman