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174
FXUS65 KPSR 201705
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1005 AM MST Fri Sep 20 2024

.UPDATE...
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Updated Aviation
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&&

.SYNOPSIS...
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A somewhat unsettled weather pattern will bring increasing rain
chances for mainly the northern portions of the region, with
continued breezy winds region-wide for today. Below normal
temperatures are expected the next couple of days before warming and
drying conditions will commence going into next week.
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.DISCUSSION...
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Strong negative height anomalies continue to persist across southern
California, as the main circulation with the longwave trough is
nearing the L.A. area early this morning. Some shower and
thunderstorm activity has continued for portions of California into
the early morning hours, with noticeably dry air in place over SE CA
and into southwestern to southcentral AZ. This drier air will limit
shower and thunderstorm potential as the strong dynamics with this
trough would otherwise provide better potential across the region.
As such, the main activity is expected to be limited primarily to
areas of best dynamics as the upper level low begins to migrate
eastward, which looks to remain along the northern fringes of the
forecast area today and tonight. The latest PoP outlook is around 30-
40% for places such as Joshua Tree NP for today, spreading eastward
across La Paz, Maricopa, and Gila Counties going into tonight. NBM
probabilities of any significant rain accumulations remain low, as
the best chances of a quarter inch or more totals are limited to
Joshua Tree NP at around 30-50%.

Aside from the rain potential, breezy winds will continue today,
more widespread across southcentral Arizona, with periodic gustiness
20-30 mph during the afternoon and early evening hours. Gusty winds
look to continue further west as well across the favored higher
terrain areas and eventually into the lower deserts of the Imperial
Valley this evening. Otherwise, temperatures will be noticeably
cooler, as the main low center will migrate across the region over
the next couple of days. High temperatures should run 5-10 degrees
below normal during this period, with lower desert lows in the mid-
60s to low 70s for the next couple of nights.

Heading into next week, the troughing feature will lift to the
northeast, with temperatures quickly rebounding back towards normal
as early as Sunday. High amplitude ridging is expected to build
across the Pacific Northwest, allowing some version of troughing,
with neutral to slightly negative height anomalies, to persist
across the region going into the middle of next week. Ensemble
clusters show some slight variance through Tuesday, but, by
Wednesday, the pattern looks to be such that the main ridge axis
will be more centered across the region, allowing temperatures to
reach several degrees above normal. There are some more noticeable
differences amongst the ensembles going into late next week, as the
next troughing feature sets up offshore of the West Coast. However,
general ridging looks to hang on across the region during this
period, resulting in continued above normal temperatures and dry
conditions.
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.AVIATION...
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Updated at 1705Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
An extended period of southerly cross runway winds early/mid
afternoon will be the greatest weather issue under occasional
scattered cloud decks 080-100ft AGL. Confidence is moderate that a
150v220 wind component will be common through late afternoon before
finally settling on the SW direction into the evening. Frequent
gusts 15-20kt should develop through the afternoon before relaxing
mid evening. Eventually overnight, a switch to an E/SE will occur
with isold SHRA over mountains north and east of the terminals. A
few SHRA may persist just outside the immediate Phoenix airspace
Saturday morning with an earlier than usual flip back to SW by late
morning.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather concerns should exist through Saturday afternoon
under periods of mid/high cloud decks. Confidence is good that W
winds will prevail through much of the period at KIPL with some
modest gusts possible this afternoon. Directions will be more
variable at KBLH with a S component favored through early this
evening.
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.FIRE WEATHER...
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A drier and cooler airmass encompassing the region will result in
below normal temperatures through Saturday. Stronger southerly to
southwesterly will develop this afternoon, with gusts to 20-25 mph
expected today, focused across higher terrain areas of the western
districts and southcentral AZ. MinRH`s will hover around 15-30%
region-wide over the next couple of days, with some slight drying
first across the western districts starting Saturday and spreading
eastward on Sunday, with MinRH`s more in the 10-20% range by the
beginning of next week. Overnight RH recoveries will be fair to good
across the region over the next couple of mornings, before degrading
to generally fair to poor in spots going into next week. Warming
temperatures to above normal are expected to develop late this
weekend and persist through most of next week.
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&&

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

&&

$$

DISCUSSION...Young
AVIATION...18
FIRE WEATHER...Young