Top of the World, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

282
FXUS66 KSGX 270450
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
850 PM PST Thu Dec 26 2024

.SYNOPSIS...
A Pacific storm will pass by to the north Friday, bringing gusty
westerly winds in the mountains and deserts. An upper ridge will
build from the southwest late Friday through the weekend. This will
result in mild days, a shallow marine layer, and cool nights this
weekend. Some offshore flow could develop early next week after
another trough of low pressure moves inland to the north.

&&

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

Satellite imagery at 9 PM was showing areas of high clouds moving
northwest to southeast across Southern California. A few patches of
low clouds were visible on satellite through breaks in the high
clouds. Any low cloud coverage overnight is expected to be patchy in
coverage. Low clouds are expected to become more widespread later in
the day Friday and overnight. Some high resolution guidance
indicates that by Friday evening the marine layer could deepen
enough for some patchy drizzle west of the mountains.

From previous discussion issued at 2 PM December 26, 2024...

A shortwave trough will pass to the north on Friday. This will
maintain conditions similar to today, with mid and high cloud cover
along with daytime temperatures near or a few degrees above seasonal
averages. Onshore flow will strengthen, with gusty westerly winds
developing over the mountains and deserts tonight into Friday. The
winds will peak Friday afternoon and evening, with gusts around 35-
45 mph in the high deserts, on the wind prone desert mountain slopes
and below passes and canyons. Winds will begin to weaken Friday
night as the synoptic pattern aloft begins to amplify and a ridge of
high pressure builds over the western states.

For the weekend...the subtropical high to our southwest will expand
into Southern California this weekend with a ridge building over the
western states. This will bring warmer conditions, with daytime
temperatures 7 to 15 degrees above normal in the valleys and
deserts, and closer to normal for the coastal areas and western
valleys as some marine layer influence remains. By Sunday morning
the marine layer could be shallow enough for another round of dense
fog in the coastal areas.

Surface pressure gradients begin to trend offshore on Monday
following the passage of another wave to our north and the
associated sfc high moving into the northern Great Basin. There
remains significant spread among ensemble solutions across model
platforms with respect to the timing and strength of the system but
the current mean solution shows about a 20 percent chance for a
moderate Santa Ana wind event sometime between Monday and Wednesday.
Whenever it occurs, we can expect warmer and much drier conditions.
Currently, it looks like next Thursday will be the warmest day, with
daytime high temperatures reaching the 80s in some locations west of
the mtns.

&&

.AVIATION...
270445Z...Coast/Valleys...Patchy low clouds and fog will occur near
the coast through Fri morning with bases 400-1000 ft MSL and tops to
1200 ft MSL, and local VIS 1-3 miles in BR. Each coastal site has a
10-30% chance of a CIG overnight, but if a CIG occurs, it will
mostly be TEMPO/short duration. A weakening weather system will move
through the region Friday afternoon and push low clouds onshore
19Z-22Z and spreading into the valleys 22Z Fri-02Z Sat. CIGs will
rise to 1200-2500 ft MSL with tops to 4000 ft MSL and areas of
terrain obscurations. Otherwise, high clouds above 20000 ft MSL will
continue through Fri morning then gradually decrease.

Mountains/Deserts...Areas of westerly winds with gusts 25-40 kt will
occur Fri from the mountain crests east through the desert mountain
slopes and over high deserts. Terrain below 4500 ft MSL will be
locally obscured Fri evening due to clouds/fog. Otherwise, high
clouds above 20000 ft MSL will continue through Fri morning then
gradually decrease.

&&

.MARINE...
Long period west-northwesterly swells will continue through early
next week. Seas will be 5-9 feet in the outer coastal waters (30-60
NM from the coast) and 3-6 feet in the inner waters (within 30 NM).
Northwest flow will strengthen slightly late Friday afternoon, with
gusts around 20 knots near San Clemente Island. Otherwise, no marine
hazards are expected through Tuesday.

&&

.BEACHES...
Another long period (15 to 17 seconds) northwesterly (280-290
degree) swell of 4-6 feet will arrive Friday and continue through
Sunday, decreasing Monday. Elevated surf of 4-7 feet is expected to
continue through early next week at San Diego County beaches with
local sets to 8 feet on west-northwest facing beaches. Minor coastal
flooding is possible in vulnerable areas during morning high tides
as tides increase through this weekend coinciding with the elevated
surf. See the Beach Hazards Statement for more information.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Sunday afternoon for San Diego
     County Coastal Areas.

     Wind Advisory from 7 AM to 7 PM PST Friday for Apple and Lucerne
     Valleys.

PZ...None.

&&

$$

PUBLIC...CO/PG
AVIATION/MARINE/BEACHES...Maxwell