150
FXUS66 KSGX 150424
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Sat Sep 14 2024

.SYNOPSIS...
A West Cosat low pressure trough will keep temperatures slightly
below averages again Sunday. The marine layer will remain deep and
result in widespread night and morning low clouds. A stronger
weather system is expected to arrive Sunday night and Monday and
bring gusty winds and further cooling with areas of light
precipitation Monday except in the deserts. A slight warming trend
will start on Tuesday but another cool weather disturbance will
enter southern California by Thursday and could bring more
precipitation.

&&

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

Update...

Stratus covered most coastal and San Diego County valley locations
and was already spreading into west and south parts of the Inland
Empire at mid-evening. Otherwise, the trough of low pressure will
continue over the West Coast through Sunday, with Sunday being
similar weatherwise to today. The latest guidance for precipitation,
including HRRR/Cansac WRF/local WRF show increasing confidence in
local orographic precipitation reaching 0.4" in San Bernardino
County Monday, with Cansac WRF very locally showing over one inch.
However, guidance still suggests most lower elevations will get 0.1"
or less out of this. Marine layer should reach 6000 feet or higher
in some locations Monday, so this will help increase humidity values
in the lower to mid mountain slopes and some ridges, though gusty
winds will occur from the ridges through the desert slopes.
Regardless, Monday will be unseasonable cool with 70s covering
almost all areas west of the mountains and only in the 80s in most
of the desert regions. System for Thursday has a lot more
variability with timing and location in the ensembles, but that has
the potential to bring more light precipitation from the coast to
the mountains and will prolong the cool spell.

From previous discussion...

An unseasonably strong upper trough will enter Socal during Sunday
night Monday. The winds will be gusty and much stronger but due to
the deep marine layer and even colder air mass the humidity will
be considerably high and widespread light rainfall and even
scattered showers with the trough passage on Monday. Wind gusts of
40 to 60 mph for wind prone mountains passes and ridges. 700 mb
southwest wind flow is forecast to be 30 to 40 knots with
temperatures down to 2C for San Gabriel mountains. Mixed out
marine layer for Tuesday and Wednesday along with a modified
warming air mass and light winds.

The pattern looks to repeat itself for mid week, with a similar
strong cold front crossing Socal by Thursday. This would also
bring some precipitation in addition to the deep marine layer. By
Friday this would shift to slight offshore flow and drying. This
system has potential to close off and dig with time which induces
the offshore wind.

&&

.AVIATION...
150300Z...Coasts/Valleys...Hazy conditions continue in the inland
valleys due to smoke from the Line and Bridge Fires in the San
Bernardino Mountains.

Low clouds with bases around 2000 ft MSL and tops to 3500 ft MSL are
increasing in coverage over the coastal areas at this hour. They are
expected to spread inland overnight, reaching into the Inland Empire
around 07Z and the lower coastal slopes by about 15Z. Similar to
previous nights, FU from the Line Fire may be trapped by the marine
later and result in VIS reductions down to 3SM for KSBD. Clearing
will begin around 16z inland, with coastal sites clearing 19Z-20z.

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 Sunday. Strong
west-northwest winds develop Sunday evening, with gusts up to 40kts
possible through the mountain passes.

&&

.MARINE...
Expect light precipitation Sunday night through Monday morning, with
less than 0.05" 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 Wednesday.

&&

.FIRE WEATHER...
Ongoing wildfires, Line, Airport and Bridge continue to be the main
weather support. South winds along the San Bernardino County ridges
with gusts to 30 MPH and persistent drier air above 6000 feet will
be the main concern Sunday. Sunday night and Monday will have
stronger southwest to west winds but increasing humidity along the
ridges. Otherwise deep marine layer and cooler air mass will
prevail. Fuel moistures that were record low are recovering quickly
except less so on high terrain.

&&

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

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...Maxwell (Update)/Tardy (Previous Discussion)
AVIATION/MARINE...PG