Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 301155

Area Forecast Discussion
National Weather Service Phoenix AZ
455 AM MST Fri Jul 30 2021

.UPDATE...Updated aviation discussion.


Shower and thunderstorm chances will continue through at least
Saturday with the main storm threats being strong winds and
locally heavy rainfall. Drier air moving into the region beginning
Sunday will quickly diminish rain chances with chances mainly
shifting over the high terrain Sunday into early next week. An
extended dry period looks likely for most of next week which will
also allow for warming temperatures, and most likely reaching a
few degrees above normal by the middle of next week.


Much of the region continues to fall under deep southeasterly
flow with the upper level inverted trough now positioned across
Sonora Mexico into southern portions of our region. Fairly deep
moisture has overspread southern Arizona and will continue to
shift westward into southeast California through the rest of the
morning. Broad ascent from difluent flow aloft remains in place
over much of Arizona, but with the inverted trough weakening and
shearing out today it will play less of a role than yesterday.
However, vertical ascent fields will remain stronger across
southern California into western Arizona supported by a south to
north oriented upper level jet positioned along the West Coast to
just west of Baja.

Latest HREF focuses storms developing across the high terrain
north of Phoenix and across Pima and maybe Pinal County, out ahead
of a MCV which will likely move into southeast Arizona by late
morning. Should also see storms develop along the Baja mtns,
possibly sending a few storms northward into Imperial County later
this afternoon. Moisture levels and instability will likely be
maximized this afternoon across the Lower CO River Valley, where
the HREF depicts fairly widespread storms possible late this
afternoon into early this evening. Yuma forecast soundings also
show a mostly uncapped profile and some modest bulk shear, so a
few strong to severe storms will be possible, on top of the heavy
rainfall and flash flood threat. For south-central Arizona into
the high terrain east of Phoenix, isolated to scattered storm
activity will be likely, but drier air working westward out of New
Mexico should decrease instability and likely storm limit

For Saturday, flow aloft shifts out of the south with the deeper
moisture shifting back across all of southern Arizona. HREF shows
higher MUCAPEs across south-central Arizona for Saturday afternoon
as moisture increases, but more limited storm activity due to a
southerly steering flow and likely weak subsidence aloft. The
threat for more widespread storms is definitely still there for
Saturday, but the latest guidance seems to be backing off on
coverage. Flow aloft should then shift out of the southwest
Saturday night into Sunday in response to the trough to our west
moving through southern California resulting in considerable
drying to begin. The drying on Sunday should mostly limit storm
potential to the high terrain north and east of Phoenix with even
less potential into early next week as PWATs likely lower to
between 1.00-1.25". Temperatures will also warm up Sunday through
the first half of next week with the subtropical high rebuilding
over Arizona and likely persisting for several days. NBM high
temperatures are shown to warm to 110-113 degrees over the western
deserts to 106-108 degrees across the south-central Arizona
deserts. The upper end of guidance shows some potential for
excessive heat, but so far the probabilities for those
temperatures remain fairly low.


.AVIATION...Updated at 1200Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Early morning shower activity is focused west of the Phoenix area,
with only a low chance (10%) of a shower affecting any area
terminal through later this morning. Otherwise, primary window for
thunderstorms will be 22Z-02Z at all area terminals, but coverage
is expected to remain isolated to scattered. More likely is the
potential for an outflow from the south or east affecting most
terminals during this period, potentially bringing wind gusts of
25-30 kts. SCT-BKN cloud bases should remain above 8-10 kft with
southerly winds persisting through most of the evening before
easterlies return overnight. Thunderstorm potential should wind
down after 02Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

Isolated showers continue across southwest Arizona this morning.
There may be a brief lull through mid-late morning, but most model
guidance suggests a chance (20-30%) of shower and thunderstorm
activity throughout most of the afternoon and evening. Confidence
is a bit higher during the early evening period at KBLH for
thunderstorm impacts, including strong outflow winds. KIPL may
also experience thunderstorm impacts slightly earlier in the
afternoon as thunderstorm activity in Baja California moves
eastward. Aside from wind gusts in excess of 30 knots from
thunderstorms, winds should generally remain below 15 knots. Cloud
bases should remain above 10 kft, except during periods of
thunderstorms where they may fall closer to 8 kft.


Sunday through Thursday:
Drier air will begin spreading across the region starting Sunday.
Chances for showers and storms on Sunday will mainly be across the
Arizona high terrain with a few isolated storms possible across
the Arizona lower deserts. Daily storm chances will continue to
diminish early next week with only isolated storms possible across
eastern Arizona. Temperatures will warm Sunday into early next
week with slightly above normal temperatures expected by the
middle of next week. Minimum afternoon humidity values will range
from 20-30% on Sunday before falling to 15-25% by Tuesday.
Overnight recovery will be mostly good to excellent in a 40-80%
range through Monday before lowering to 25-60% later in the
period. Apart from thunderstorms, winds will favor typical daily
upslope/drainage patterns.


Spotters should follow standard reporting procedures.


AZ...Flash Flood Watch from noon MST today through late tonight for

CA...Flash Flood Watch from noon PDT today through late tonight for



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