999
FXUS66 KSGX 152053
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
153 PM PDT Sun Sep 15 2024

.SYNOPSIS...
Cooler west of the mountains today, with a deep marine layer. Breezy
winds expected into the deserts this afternoon and evening.
Continued cooling with a chance of light precipitation over and west
of the mountains Monday. Winds will increase in strength for Monday.
Brief warming expected on Tuesday before cooler, windier, and
additional chances of light precipitation enter the forecast by
Thursday. Warmer Friday into the weekend as ridging builds in from
the west.

&&

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

An upper level low pressure system digging south into California
from the Pacific Northwest will increase onshore pressure gradient
for Monday. The increased onshore flow will deepen the marine layer
to 5500-6000 ft and will produce areas of light showers west of the
mountains and on the coastal mountain slopes. For the coastal areas
and valleys, rainfall totals will generally be 0.05 to 0.15 inches.
High-res guidance is still suggesting higher amounts on the south
facing slopes of the San Bernardino Mountains. The HREF has a 50-70%
chance of total rainfall accumulations greater than 0.50 inch for
portions of the coastal slopes of the San Bernardino mountains, and
a 20% chance of greater than 1 inch. Much of the shower activity
will occur Monday morning. More isolated shower activity is possible
into Monday afternoon along the coastal slopes of the mountains. An
embedded shortwave will move across the area Monday night into early
Tuesday. That may spark another round of isolated showers Monday
night into early Tuesday, most likely in San Diego County.

Southwest to west winds will begin to increase this afternoon and
evening for the desert mountain slopes, deserts, and passes. Peak
wind gusts for the desert slopes of the mountains and into the
deserts will be 35 to 45 mph, with a few local gusts to 50 mph
possible through the San Gorgonio Pass. Winds are expected to
strengthen for Monday afternoon and evening. The strongest winds are
expected through passes and into the deserts. There is a 60 to 70%
chance of gusts greater than 55 mph below the San Gorgonio Pass and
along I-8 near the Imperial County border. Forecast peak gusts are
be 45 to 55 mph, with a few local gusts to 60 mph possible.

Deep boundary layer moisture will still be in place for the middle
of the week, but with a weakened/non-existent marine inversion cloud
coverage may be patchy. Brief warming will occur Tuesday with a
minor cooling on Wednesday as another trough digs south along the
California coast. There remains spread amongst the ensembles in
exact timing of the trough passage. This introduces some uncertainty
in the forecast, particularly surrounding high temperatures on
Wednesday and Thursday as well as timing of any precipitation and
gusty winds. Current forecast has minor change in temperature from
Wednesday to Thursday and best chance of precipitation Wednesday
night into early Thursday for areas in and west of the mountains.
The forecast also has the strongest winds Wednesday night into
Thursday for desert mountain slopes, deserts, and through passes. As
the trough moves east ridging will build in from the west for Friday
into the weekend for warmer and fair weather. There is the potential
for weak offshore flow sometime next weekend as an upper low/inside
slider moves into the Great Basin, but confidence is low. If any
offshore flow develops, it would contribute to additional warming
west of the mountains.

&&

.AVIATION...
152000Z...Coasts/Valleys...Hazy conditions continue in the inland
valleys due to smoke from the Line and Bridge Fires in the San
Bernardino Mountains. Low stratus with varying bases from 2000-
3200ft MSL and tops to 4200-4500ft MSL continues for the coasts and
far western valleys, but should continue to see slow clearing this
afternoon. There is a 40-60% chance that full clearing does not
occur for the San Diego County coasts this afternoon with CIGs
continuing through the evening, but intermittent scattering may
occur at times. Stratus pushes up to 30 miles inland again this
evening between 23-01z with bases likely a few hundred feet higher
than this morning. Light rain showers/drizzle will be possible after
03z with very low accumulation expected. Similar to previous nights,
FU from the Line Fire may be trapped by the marine later and result
in VIS reductions down to 2SM for KSBD with the only other VIS
reductions seen where marine clouds intersect higher elevations.
Clearing on Monday looks to be similar to what was observed today.


Mountains/Deserts...Smoke from the Line and Bridge fires will
produce localized VIS restrictions near the San Bernardino County
Mountains, and the Airport fire will produce similar conditions in
the Santa Ana Mountains through Monday. Strong west-northwest winds
develop this afternoon/evening, with gusts up to 40kts possible
through the mountain passes, continuing into Monday. Light rain will
be possibly tonight into Monday for the coastal slopes of the mountains,
with little impacts expected. Up to 0.25" will be possible.

&&

.MARINE...
Expect light precipitation Sunday night through Monday morning, with
less than 0.10" expected. Winds will strengthen from the west to
northwest in the outer coastal waters Monday and Monday night, with
gusts up to 20kts likely. Otherwise, no hazardous marine conditions
are expected through Friday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 7 PM this evening to 9 PM PDT Monday for
     Apple and Lucerne Valleys.

     Wind Advisory from 11 AM Monday to midnight PDT Monday night for
     San Diego County Deserts.

     Wind Advisory from 7 PM this evening to midnight PDT Monday
     night for San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...CO
AVIATION/MARINE...Zuber