000
FXUS66 KSGX 062033
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
133 PM PDT Thu Oct 6 2022

.SYNOPSIS...
Slow and slight warming will continue for coastal and valley
locations through Saturday. A general cooling trend will then
follow through the middle of next week as the upper-air pattern
shifts. An upper level cutoff low looks to form over NW Mexico
which will allow for additional moisture to funnel into SoCal,
leading to chances for isolated to scattered thunderstorms over
the mountains through much of this weekend and into early next
week. Notably cooler conditions and some breezy winds can be
anticipated next week as an upper level trough sets in over the
western US.

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

Forecast Highlights:
1. Daily chances for thunderstorms over the mountains, potentially
   some of the coastal valleys as well
2. Cooling trend this weekend through the middle of next week
3. Gradually shrinking marine layer through the weekend

The development of a coastal eddy and a strong low-level
inversion has allowed for coastal low clouds to remain in place
for much of this afternoon with little to no additional clearing
expected along/near the immediate coast. The marine layer should
become more shallow this evening as an upper level ridge settles
in over the Eastern Pacific, shrinking from nearly 2500 of depth
this morning to closer to 1500-2000ft. Some isolated instances of
drizzle are possible Friday morning but overall much less coverage
is anticipated. Expect a gradual shallowing trend with the marine
layer through the weekend as the ridge becomes settled in.

Highs will steadily warm through the next few days for the coasts
and valleys while the deserts and mountains see their warmest
temperatures today. Highs ultimately top out 3 to 7 degrees above
seasonal normal for the mountains and deserts, translating
generally to the upper 70s to middle 80s in the mountains while
the deserts hit the upper 90s, approaching 100 degrees. Steady
cooling then sets in for the mountains and deserts as the upper
ridge axis retrogrades a bit westward and a cutoff 500mb low
develops over NW Mexico. The coasts and valleys warm up a bit
through Saturday with the Inland Empire seeing highs reach into
the 90s while the coastal valleys hit the upper 80s. The
development of a broad 500mb trough over much of the western US
this weekend and early next week will lead to a cooling trend
through the middle of next week, with much of SoCal potentially
dropping well below seasonal averages by next Wednesday. Some
areas could potentially see highs topping out on the order of 10
degrees below average.

The aforementioned cutoff 500mb low over NW Mexico will also
allow for more of a moisture flux to enter into SoCal. This will
support chances for at least isolated thunderstorms developing
over mountainous terrain each day through the early portions of
next week. PW values near and exceeding 1.0 inch continue to build
in and increase over portions of Imperial and eastern San Diego
Counties, with a noted PW gradient over Riverside and San
Bernardino Counties illustrating the stark boundary between moist
and dry air. This will keep the more favored storm chances
generally in the San Diego County Mountains today and Friday. Some
easterly flow of 10-15kts between 700-500mb was noted on the 12z
Miramar sounding, which may allow for some thunderstorms to
develop and drift into portions of the San Diego Valleys this
afternoon. Little change in the upper pattern is expected through
Friday so this potential may occur again on Friday.

Through the weekend, enough moisture will continue to build up
across SoCal in this oddly summer-like pattern, supporting more
chances for scattered thunderstorms across all of the mountains
and even some of the adjacent deserts and valleys. Ensemble
precipitation guidance indicates a rather persistent signal for at
least some low-end storm chances through much of next week.
Ensemble PW guidance generally peaks in most areas in and east of
the mountains for Sat-Sun-Mon, namely on Sunday. A few ensemble
members suggest PW exceeds 1.0 inch again in the deserts and even
some mountain locations including Campo on these days. Will
maintain the highest PoPs during this time frame accordingly.

&&

.AVIATION...
061945Z...Coast/Valleys...OVC005-015 tops 022 at the coast and over
the coastal waters spreading 25 miles inland into the valleys
through 15Z Fri with vis lowering to 1-4SM in fog/haze from 10-19Z.
Skies clearing back toward the coast through 21Z Fri but CIGS may
persist at KSAN/KCRQ throughout the day.

SCT-BKN100 cumulus over the mountains this afternoon and again
Friday afternoon with iso TSRA. Some storms will drift west off the
mountains and over the inland valleys.

&&

.MARINE...
No hazardous marine weather is expected through Monday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...Adams
AVIATION/MARINE...Moede




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