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791
FXUS65 KPSR 211804
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1104 AM MST Sat Sep 21 2024

.UPDATE...
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Updated Aviation discussion.
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&&

.SYNOPSIS...
An unsettled weather pattern will calm going through today, with
quieter weather conditions moving forward through this upcoming
week. Cooler than normal temperatures will trend warmer to above
normal readings by early next week.

&&

.DISCUSSION...
A potent upper level low centered over western Arizona is
continuing to spark some low-topped showers and storms across the
eastern portions of the region, now primarily east of the Phoenix
metro. Otherwise, dry air, as seen in WV imagery, is preventing
more widespread activity, as the main activity is along the
frontal boundary and near the cold core of the upper low. As this
upper low continue to track eastward across the northern portions
of the forecast area, shower and storm coverage is expected to
likewise shift eastward, with limited convective potential during
the daytime hours across northern Maricopa and central Gila
Counties. Due to the anomalously cold upper level low overhead,
temperatures will continue to remain below normal, with today
expected to be the coolest day across southcentral Arizona over
the next week.

As the negative height anomalies traverse eastward in association
with this upper low going into tomorrow, a quick response in
warming temperatures will occur, as mid-level heights build in
from the west. However, general longwave troughing will continue
to persist across TX, NM, and even into eastern AZ going into
early next week, resulting in temperatures only warming to a few
degrees above normal across the region. High amplitude ridging in
association with strong positive height anomalies will develop
across the Pacific Northwest and into the Intermountain West early
in the week, and persisting into the middle portions of the week.
A weak shortwave riding along the eastern periphery of this ridge
will keep this longwave troughing persisting into the middle of
next week. Ensembles remain in good agreement with this general
pattern during this period.

Stronger positive height anomalies are expected to move into the
Desert Southwest going into the latter portions of next week, as
the main ridge axis sets up over Arizona. However, temperatures
will remain just a few degrees above normal as the strongest
anomalies remain well to the north, as the aforementioned longwave
troughing across the Southern Plains continues to persist. Another
strong trough originating from the Gulf of Alaska will also begin
to impinge on the Pacific Northwest as well at this point, but
isn`t expected to have any influence on any potential changes to
the weather pattern here locally going into next weekend.
Ensembles show a bit more divergence in the weather pattern,
especially in regards to the persist troughing across central
CONUS going through the end of the week. However, weak ridging is
expected to persist across the region, keeping dry conditions and
above normal temperatures across the region going into next
weekend.

&&

.AVIATION...
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Updated at 1804Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

An upper low centered near KFLG will is tracking northeastward and
will exit AZ by tonight. Due to limited moisture availability,
cloud cover over south-central AZ is limited to SCT cumulus
over/near the higher terrain east of the Valley (bases AOA FL070)
with only FEW cumulus near the TAF sites. The cumulus over the
higher terrain will diminish shortly after sunset. Westerly
surface winds have started to take hold and a westerly component
will continue into the evening hours (northwesterly being common
in the late afternoon and early evening). Anticipate occasional
minor gustiness (less than 20kts) this afternoon as well.
Anticipate familiar nocturnal wind patterns developing after 04Z.


Southeast California/Southwest Arizona including KIPL and KBLH:

Light north winds (less than 10kts) will be common this afternoon
before light and variable conditions predominate tonight.
Otherwise, clear skies.
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&&

.FIRE WEATHER...
Some isolated shower and storm activity may persist into the
morning hours across the eastern districts, but will result in
only brief rain and low CWR`s (generally less than 10%).
Otherwise, a drier and cooler airmass encompassing the region
will result in below normal temperatures through today. More
traditional diurnal winds patterns will encompass the region over
the next several days. MinRH`s will hover around 15-30% region-
wide through today, with some slight drying across the region
starting tomorrow, with MinRH`s more in the 10-20% range by the
beginning of next week and extending into the middle of next week.
Overnight RH recoveries will be fair to good across the region
through tomorrow morning, before degrading to generally fair to
poor in spots going through the middle of next week. Warming
temperatures to above normal are expected to develop tomorrow and
persist through most of next week.

&&

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

$$

DISCUSSION...Young
AVIATION...AJ
FIRE WEATHER...Young