052
FXUS66 KSGX 151556
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
856 AM 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...

Visible satellite at 9 AM this morning was showing low clouds had
filled in the coastal basin and had made it into mountain passes.
A few areas of drizzle have been reported, mainly in the valleys.
High temperatures today are expected to be a few degrees cooler
than yesterday for most locations. The exception is high
temperatures for some desert locations may be a degree or two
warmer than yesterday. An upper level low pressure system is still
on track to dig south into California tonight through Monday.
That is expected to bring additional cooling to the entire area,
an uptick in winds for the deserts and desert mountain slopes, and
areas of light precipitation in and west of the mountains. Highs
on Monday are expected to be 15- 25 degrees below normal inland,
and around 5-10 degrees below normal near the coast.

The increased onshore pressure gradient from the low pressure system
will help 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 less than one-tenth inch. High-res guidance 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" for portions of the coastal slopes
of the San Bernardino mountains, and a 20% chance of greater than
1". Much of the shower activity will occur Monday morning through
the early afternoon hours.  An embedded shortwave will move across
the area Monday night into early Tuesday. That may spark another
round of shower activity Monday night into early Tuesday, mainly
across San Diego County.

Southwest to west winds will begin to increase this afternoon and
evening. Peak wind gusts for the desert slopes of the mountains and
into the deserts will be 35 to 45 mph. Winds are expected to
strengthen for Monday afternoon and evening. The strongest winds are
expected through passes and into the deserts. Below the San Gorgonio
Pass and along I-8 near the Imperial County border where there is a
70-80% chance of gusts over 50 mph.

Brief warming will occur Tuesday with little change in temperatures
for Wednesday as the upper low departs but weak troughing remains
across the West Coast. Deep boundary layer moisture will still be in
place, but with a weakened/non-existent marine inversion any cloud
coverage will be rather patchy. Another closed low dives down the
coast and moves across So Cal sometime late Wednesday into Thursday,
though there remains spread amongst the ensembles in exact timing.
This low will bring cooling, another round of breezy conditions in
the mountains and deserts, and potentially more light precipitation
for the mountains westward. The trough moves east with ridging
eventually building 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...
1501500Z...Coasts/Valleys...Hazy conditions continue in the inland
valleys due to smoke from the Line and Bridge Fires in the San
Bernardino Mountains. Stratus with varying bases around 2900-3200ft
MSL and tops to 4200ft MSL have filled in across all coasts/valleys
this morning. 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. Clouds will start to clear San
Diego County valleys 16z-17z, the Inland Empire 17-18z, and 19-20z
for the Orange County coast. Clouds may not break across the San
Diego County coasts through the afternoon (40-60% chance) but may
experience intermittent scattering at times. Stratus pushes up to 30
miles inland again this evening after 01z with bases likely a few
hundred feet higher than this morning. Light rain showers are also
possible after 03z.

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. This will continue through at least Monday
morning. Strong west-northwest winds develop this afternoon/evening,
with gusts up to 40kts possible through the mountain passes,
continuing into Monday.

&&

.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 20-25 knots likely. Otherwise, no hazardous marine conditions
are expected through Thursday.

&&

.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.

PZ...None.

&&

$$

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