Placentia, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

218
FXUS66 KSGX 181129
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
329 AM PST Sat Jan 18 2025

.SYNOPSIS...
Onshore flow will continue to bring cooler weather and partly
cloudy skies west of the mountains during the nights and mornings
into Monday. Offshore flow will develop late Monday with Santa
Ana Winds late Monday through Tuesday, and possibly again
Thursday.

&&

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

This morning...Surface pressure gradients remain strong enough
onshore to support westerly wind gusts of 30-40 mph in the
windiest locations. Temperatures are mostly about what they were
24 hours ago except in the low deserts where they are generally a
few degrees cooler. The marine layer remains about 3 thousand ft
deep with low clouds covering much of the coastal foothills and
increasing in coverage across the coastal areas and inland
valleys.

Weakening onshore sfc pressure gradients will result in a diurnal
wind pattern through Sunday, with downsloping winds at night and
a sea breeze in the afternoons. This will continue low clouds for
the coastal areas and valleys tonight and again Sunday night.
Daytime temperatures will remain somewhat below seasonal averages
for the lower elevations west of the mtns through Sunday.
Overnight low temps will remain below seasonal averages west of
the mountains through Sunday night, and some low-lying areas of
the inland valleys could experience frost.

Sfc high pressure moving into the Great basin and setting up
strong offshore pressure gradients, along with a shortwave trough
moving south out of Canada in the mean flow aloft will likely
produce another Santa Ana wind event early next week. With the
shortwave trough providing upper level support, the northeast to
east winds will likely peak Monday night/Tue morning with gusts
locally reaching 60-65 mph in the windiest locations. As we would
expect, humidities will drop into the single-digit range by Tue
afternoon for all areas inland of the immediate coast. After that
shortwave passes to the east, the winds will weaken as upper
support is lost and offshore sfc pressure gradients weaken.
Daytime high temperatures will rise but remain near or slightly
below seasonal averages due to the cold air advection opposing the
compression warming as the air flows downhill out of the Great
Basin.

A second shortwave trough will follow later in the week but will
likely take a more inland track which would be less effective at
lending upper support so that the next surge of offshore winds for
Thu/Fri will likely not be as strong as the Mon/Tue event.
Humidities will remain low for inland areas through Friday.

Onshore flow with lower temperatures, increasing humidity and a
return of marine layer low clouds could return for next Saturday.

&&

.AVIATION...
181020Z...Stratus based at 2500-3500ft MSL continues to linger this
morning. Coverage is generally SCT-BKN along the coasts and more OVC
in the Inland Empire, while the San Diego County valleys remain
clear. These clouds should clear 15-18z this morning.

Low clouds look to redevelop and move inland after 04-06z this
evening with likely lower bases than this morning with a more
typical full coverage marine layer. Bases will be around 1000-1500ft
MSL. VIS restrictions 4-6SM possible along the coasts with locally
lower VIS within valleys and on coastal higher terrain.

NWS San Diego is aware of limited communications of observations
from KTRM since January 8th. We are working with the FAA to address
this issue.

&&

.MARINE...
No hazardous marine conditions are expected through Wednesday.

&&

.FIRE WEATHER...
The next Santa Ana event now seems likely for late Monday into
Tuesday. It will bring very dry air into the entire region, and
strong northeast to east winds to foothills, adjacent inland valleys,
and into interior Orange County. Strongest gusts in the foothills
will be 45-60 mph Monday night and Tuesday morning, with humidity
dropping to 5-15 percent away from the coast on Tuesday. A Fire
Weather Watch is in effect for Monday through Tuesday. Winds will
weaken late Tuesday and Wednesday but remain offshore, with very
little humidity recovery. Another Santa Ana episode could develop
for Wednesday night and Thursday. Current guidance indicates that
this second episode will likely be weaker than the Monday-Tuesday
one.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Fire Weather Watch from Monday morning through Tuesday evening
     for Orange County Inland Areas-Riverside County Mountains-
     Including The San Jacinto Ranger District Of The San
     Bernardino National Forest-San Bernardino County Mountains-
     Including The Mountain Top And Front Country Ranger
     Districts Of The San Bernardino National Forest-San
     Bernardino and Riverside County Valleys  -The Inland Empire-
     San Diego County Inland Valleys-San Diego County Mountains-
     Including The Palomar And Descanso Ranger Districts of the
     Cleveland National Forest-San Gorgonio Pass Near Banning-
     Santa Ana Mountains-Including The Trabuco Ranger District
     of the Cleveland National Forest.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...PG
AVIATION/MARINE...Munyan