High Wind in California, December 12, 2024

Area Forecast Discussion
National Weather Service San Diego CA
1148 AM PST Thu Dec 12 2024

.SYNOPSIS...
Cooler onshore flow and a trough of low pressure will bring more
clouds and scattered light showers late this afternoon and
evening from the coast to the mountains. Partly cloudy skies and
slightly warmer weather are expected this weekend. High pressure
will gradually build next week, bringing some offshore flow and
dry and warmer weather.

&&

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

A low pressure trough pushing through NorCal this morning will
arrive in SoCal this afternoon. Clouds at all levels will increase
and lead to scattered showers moving from northwest to southeast.
Amounts will be pretty tiny, less than 0.10 inch for the wettest
spots in foothills. 0.00 to a few hundredths is most likely for
the coast and valleys.

Westerly winds will increase during the day and peak
late afternoon through evening. Strongest winds will hit the
mountains and deserts, where top gusts over ridges and into desert
slopes will reach 35-45 mph. For most of us, the most sensible
thing will be the cooler and more humid air rushing into our
dessicated region. Highs will be in the 60s west of the mountains,
40s and 50s in the mountains, near 60 in the high desert, and
lower to mid 70s in the low desert. The fast-moving trough will
exit by Friday morning, leaving us with a fair and dry day, but
still cool.

Another low pressure trough, embedded in a strong Pacific jet
stream, arrives in California Saturday. Similar to today's system,
it will bring more clouds and some showers Saturday night, but
unlike today's system the showers are mostly going to remain in
L.A. and points north... only a 10-15% chance of measurable rain
for Orange County. Onshore winds will increase Saturday, but won't
be overly strong.

On Sunday, high pressure aloft begins to build,but yet another
trough of low pressure moves into California Monday. This one has
decent consensus from ensemble guidance to remain farther to our
north, with no real sensible impact to SoCal. It will move into
the interior West, bringing a pool of colder air into that region.

You know what that means...increasing surface pressure there and
a developing offshore pressure gradient. Yesterday there was a big
spread in possible outcomes, but today there is a smaller range.
It looks like we'll get increasing chances of offshore flow
Tuesday into Thursday. Right now it doesn't look overly strong,
but we'll have to wait and see. In the meantime, high pressure
aloft amplifies over the West and that will lead to unseasonably
warm weather (possibly 80 degrees?) as we approach the winter
solstice.

&&

.AVIATION...
121700Z....Coasts/Valleys...SCT-BKN marine layer clouds with CIGs
around 1500ft MSL have already developed for coastal San Diego
County this morning, but intermittent periods of scattering at
KSAN/KCRQ remains possible through the late morning/early afternoon
hours. More widespread CIGs will develop/push in around 21-00z this
evening, with bases 2000-3000ft MSL and tops to 4000ft MSL. Isolated
to scattered SHRA will move west to east 23-06z this evening, with
the potential for local VIS reductions to 4-6 SM. After 06z, clouds
become more SCT-BKN again, with full clearing expected around 12-18z
Friday morning.

.Mountains/Deserts...Westerly surface winds gusting 30-40 kt in
the mountains and on desert slopes late this morning through this
evening, resulting in areas of up/downdrafts. SCT-BKN clouds below
6000ft MSL expected to increase around 22-00z this evening on the
coastal slopes leading to local VIS reductions of 0-5SM where clouds
intersect terrain. Very isolated -SHRA will move west to east 02-07z
mainly in San Diego County and the Santa Ana Mountains. Impacts will
be minimal, with gradually cloud cover clearing expected from 12-18z
Friday morning.

&&

.MARINE...
Stronger northwest winds are expected through this evening over the
outer coastal waters. Peak gusts of around 25 kt will occur, mainly
near San Clemente Island. See the Small Craft Advisory for further
details.

&&

.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 morning for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Wind Advisory until midnight PST tonight 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 until 10 PM PST this evening for Waters
     from San Mateo Point to the Mexican Border Extending 30 to
     60 nm out including San Clemente Island.

&&

PUBLIC...Suk
AVIATION/MARINE...Munyan