Portola Hills, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

300
FXUS66 KSGX 232148
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
148 PM PST Mon Dec 23 2024

.SYNOPSIS...
Periods of high clouds expected through the day. Dense fog is
expected within 10 miles of the coast this evening into early Tuesday
morning. Gradual cooling is expected through Wednesday. Breezier
and wetter weather is expected for Tuesday afternoon and
overnight. Dry conditions return by Wednesday morning. Gradual
warming is expected Thursday into the weekend.

&&

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

Visible satellite 1 PM was showing high clouds streaming north to
south across the area with low clouds along the coast and over
the coastal waters. Webcams from beach locations where clouds are
on the immediate coast are showing limited visibility and the
camera on the San Clemente basin buoy (roughly 60 nautical miles
offshore) is showing the cloud deck on the surface of the ocean.
Low cloud and fog coverage is expected to expand along the
immediate coast this evening, moving inland tonight. Areas of
dense fog are possible west of Interstate 15 in San Diego County
and west of Interstate 5 in Orange County. Onshore flow will
increase Tuesday morning ahead of an incoming upper level trough,
which should deepen the marine layer and spread fog further inland
reducing dense fog concerns for the coast and western valleys
after sunrise.

The incoming trough of low pressure will move across the West Coast
Tuesday bringing breezy and wet conditions to the area. Onshore
westerly winds will increase Tuesday afternoon, peaking Tuesday
night, strongest in the mountains, through passes, and into the
deserts. Current forecast has peak wind gusts of 45 to 55 mph, with
local gusts up to 60 mph in wind prone locations. A band of rain
showers is expected to start in Orange and San Bernardino counties
late Tuesday afternoon and quickly move to the southeast, with
showers ending in San Diego County very early Wednesday morning.
Winds at 700 mb look like they will range between 40 and 55 knots
which will promote orographic enhancement on west facing mountain
slopes. Rainfall totals for the mountains are 0.20 to 0.40 inches,
with the totals closer to 0.40 inches more localized to west facing
mountain slopes. For the coast and valleys rainfall totals are
expected to remain mostly 0.10 inch or less, with a few locally
higher amounts closer to the mountain foothills. Some locations in
the High Desert may accumulate a few hundredths of rain. A few
inches of snow are expected above 7000 ft. This is a progressive,
quick moving trough so dry conditions are expected for much of the
daylight hours on Wednesday.

Temperatures on Wednesday are expected to be a few degrees cooler
than Tuesday. That will bring highs to at or slightly below normal
for this time of year west of the mountains and 3 to 5 degree warmer
than normal in the deserts. A series of Pacific storms are expected
to move across the Northwestern United States into the beginning of
January. Latest global model ensemble guidance is indicating that a
ridge will build over California from the southern east Pacific
ocean which will largely prevent any of the passing Pacific storms
from digging far enough south to bring us any precipitation. The
current forecast has dry conditions with a gradual warming trend
Thursday through Monday. There remains some uncertainty in the
tracks of the lows passing to our north, but if any dig south into
the Great Basin or Intermountain West there could be periods of
offshore winds. Currently no guidance is indicating impactful
winds through the forecast period. With the ridge building aloft
and continued weak onshore flow, coastal dense fog could be a
concern for later in the week.

&&

.AVIATION...
232130Z....Coasts/Valleys...Areas of BKN clouds with bases around
500 ft MSL lingering near La Jolla and Pt. Loma, but otherwise low
clouds and fog have retreated offshore for this afternoon. Low
clouds will push rapidly inland this evening 00-04Z Tue. Bases may
initially start out around 400-700 ft MSL but will likely rapidly
lower to 100-400 ft MSL by about 06Z. Along with these, we will
likely see a period of VIS restrictions 0-3 SM along the coast, with
areas of dense fog with VIS <1/2 SM, including likely at KSAN and
KCRQ. Most probable period is 06-12Z, but could start as early as
about 04Z and last as late as 16Z Tue.

A low pressure system moves into the region early Tues morning,
which will lead to gradually rising bases after 12Z Tues with more
significant improvements after about 15Z, when bases are expected to
rise above 1000 ft MSL and clouds start to push eastward into the
valleys. Bases will continue to rise into the late afternoon, but
VIS 3-6 SM in BR could last into the afternoon, and overcast
conditions continue along the coast all day. Some light drizzle is
possible along the immediate coast Tuesday morning, but rain not
likely until 00Z Wed, after which precipitation will spread from
west to east across the region through about 05Z. Heavier showers
will lead to locally lowered bases 1000-2000 ft MSL and VIS 2-5 SM.
Clouds will start to break up late Tuesday evening.

.Mountains/Deserts...SCT-BKN high clouds mostly at/above 20,000 ft
MSL with unrestricted VIS will prevail through Tuesday afternoon.
Clouds at 3000-6000 ft MSL or so will move into after 20Z Tues,
leading to terrain obscurations. Precipitation will then move across
the area from west to east after 00Z through 06-08Z Wed. Locally
lower CIGs and VIS under showers. Deserts will see some high cloud
cover but very likely remain dry. Additionally, winds will pick up
over ridges and higher terrain after 18Z Tue, with gusts to 30-45 kt
and mod to strong updrafts/downdrafts near the mountains in the
evening.

&&

.MARINE...
Fog with visibilities around 1 NM likely this evening through late
tonight. Visibility will improve early Tuesday morning. Long period
(16-20 second) west to northwest swells (280-290 deg) will continue
to move through the coastal waters through late Tuesday, with the
highest swells in the outer coastal waters where a Small Craft
Advisory is in effect. Seas of 8-12 feet for the outer coastal
waters and 7-9 feet within 30 NM of the coast. These long period
swells are also leading to locally steep and difficult conditions
near Zuniga Shoal.

Late Tuesday evening into early Wednesday morning, northwest winds
will increase to 15-25 knots with gusts to 25-30 knots, strongest in
the outer coastal waters. In addition, wave periods will shorten,
leading to steeper and rougher seas throughout the coastal waters.
The Small Craft Advisory has been extended to the inner coastal
waters Tuesday evening through early Wednesday morning. Waves
diminish slight and become less steep late Wednesday. Additional
long period swells will continue to move into the region the second
half of the week, but wave heights will be a bit lower at 6-9 feet.

&&

.BEACHES...
Long period (16-20 second) west to northwest swells (280-290 deg)
will produce high surf of 6-12 feet with locally higher sets through
Wednesday. Highest surf expected for west facing beaches. This will
make swimming hazardous and pose a minor coastal flooding threat.
Elevated surf will continue late in the week as additional, albeit
somewhat smaller, swells occur. See the High Surf Advisory for more
details.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 4 AM PST Wednesday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Wind Advisory from 4 PM Tuesday to midnight PST Tuesday night
     for Apple and Lucerne Valleys-Coachella Valley-Riverside
     County Mountains-San Bernardino County Mountains-San Diego
     County Deserts-San Diego County Mountains-San Gorgonio Pass
     Near Banning.

PZ...Small Craft Advisory from 4 PM Tuesday to 4 AM PST Wednesday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm.

     Small Craft Advisory until 4 AM PST Wednesday for Waters from
     San Mateo Point to the Mexican Border Extending 30 to 60 nm
     out including San Clemente Island.


&&

$$

PUBLIC...CO
AVIATION/MARINE/BEACHES...Westerink