288
FXUS66 KSGX 062221
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
221 PM PST Mon Jan 6 2025

.SYNOPSIS...
Warmer for the mountains and little cooler for coast and valleys
today. Cooler conditions are expected for Tuesday and Wednesday with
strong and gusty north to northeasterly Santa Ana winds. Critical
fire weather conditions are expected for some areas Tuesday, with
widespread critical fire weather conditions expected Wednesday.
Warmer conditions expected for Thursday and Friday with weaker Santa
Ana winds.

&&

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

A colder low pressure system from the north will move
quickly southward into the area tonight with strong north to
northeast flow aloft for Tuesday into Wednesday. High temperatures
on Tuesday continue to cool, with a few degrees of continued cooling
for the coast and valleys and more significant cooling for the
mountains and High Desert. The southward progression of the low will
generate northerly flow at the surface over Point Conception which
should generate a coastal eddy over the California Bight tonight.
That should bring low clouds and fog back to coastal areas tonight.

Moisture from the low is expected to reach the deserts and eastern
mountain slopes Tuesday as it digs south towards the
California/Arizona border. The moisture influx may generate a few
light showers on the desert facing mountain slopes. There is a 15 to
20 percent chance of showers in the San Bernardino Mountains Tuesday
morning and afternoon. Shower chances decrease by Tuesday evening.
Chances of showers are closer to 10 percent for Riverside and San
Diego County mountains. Snow levels will fall to 5500 feet early
Tuesday morning falling to 4000 to 4500 feet for the late morning
and afternoon.

There is higher confidence in winds picking up earlier in the day
Tuesay for Orange County, the Inland Empire, and San Bernardino
county mountains. The High Wind Warning has been adjusted to capture
the uptick in winds Tuesday morning. The model guidance is also
showing a more significant drying trend, especially for lower
elevations on Tuesday with humidity values dropping near 10 percent.
Given the recent trends, periods of critical fire weather conditions
are expected Tuesday. Northeast winds are expected to arrive in San
Diego county later in the day Tuesday. Winds are still expected to
peak Tuesday night into Wednesday morning across the region. By
Wednesday, more dry air will be in place with widespread critical
fire weather conditions expected where relative humidity values will
lower into the single digits. More details in wind speeds and
humidity levels can be found in the fire weather discussion below.
Latest guidance is showing the potential for a secondary peak in
winds for Thursday morning, mainly for mountain locations and the
Inland Empire. Some guidance continues to show the potential for
moderate winds on Friday, but confidence is low at this time.

Warming is expected on Thursday with slight cooling for the coast
and valleys on Friday as the mountains and deserts continue to warm.
The general pattern for the latter half of the week going into next
weekend will be high pressure aloft over the eastern Pacific into
British Columbia with northerly flow across the western states.
There are some model differences in the timing and strength of
mostly weak weather systems moving southward across the area. Ahead
of these systems it will generally be a little warmer with weaker
winds with it a little cooler and breezy behind them.

&&

.AVIATION...
062140Z...Mostly clear skies except for FEW-SCT clouds at/above
20000 ft MSL will continue today and tonight. Low clouds with bases
near 600-900 ft MSL may develop as early as 03z this evening for
coastal airports. 70% chance for low clouds in the vicinity of KSAN
and 30-50% chance elsewhere along the coast. Any coastal low clouds
should dissipate by 14z as winds become offshore. SCT-BKN clouds
with bases near 8000-10000 ft MSL will develop for the eastern San
Bernardino Mtns 12Z Tues-00Z Wed. 20% chance of -SHRA/-SN.

A Santa Ana winds event will begin to unfold Tuesday morning with
gusty N to NE winds beginning around 12z for the mountains and
Inland Empire between KONT and KRAL. Winds will continue to
strengthen and expand to include most of Orange County and the
Coachella Valley by 18z. Widespread wind gusts of 25-40 kts in these
areas with gusts of 40-50 kts or higher for parts of the mountains
and Inland Empire. LLWS and moderate to strong updrafts and
downdrafts are likely where Santa Ana winds are present, especially
near the coastal slopes of the mountains including VCTY KONT and
KSNA. Looking ahead, continued gusty N to NE winds will fill in to
include all areas Tuesday evening into Wednesday.

&&

.MARINE...
No hazardous marine conditions are expected through early Tuesday.
Offshore winds of 20-30 kt are expected late Tuesday morning through
Wednesday morning, with a 70% chance that they will exceed 30 kt in
the outer coastal waters. This will result in choppy and hazardous
conditions. NE winds locally over 20 kts on Thursday with lower
confidence. No additional hazardous marine conditions Friday into
the weekend.

&&

.FIRE WEATHER...
Moderate to strong northerly to northeasterly Santa Ana winds
will develop Tuesday morning, with widespread gusts of 50 to 60
mph along the coastal slopes of the San Bernardino Mountains,
below the Cajon Pass, and into the Santa Ana Mountains and
Foothills. Gusts 35 to 45 mph are possible into the Inland Empire
below the Cajon Pass and near the foothills of the Santa Ana
mountains in Orange County. Relative humidity on Tuesday is
trending drier for locations north of San Diego County. Orange
County and the Inland Empire may see relative humidity values 10
to 15 percent Tuesday afternoon, with higher humidity closer to 20
percent in the Santa Ana mountains. The San Bernardino mountains
will be slow to dry out due to an influx of mid-level moisture
into the area. On the coastal slopes of the mountains lowest
afternoon relative humidity will be 20 to 30 percent with higher
relative humidity on the desert facing slopes. Winds will be
slower to develop and relative humidity will be slower to fall in
San Diego County and Riverside County mountains. Winds will become
northeasterly by Tuesday afternoon in Riverside County mountains,
with northeasterly winds reaching San Diego county around sunset.
Afternoon humidity values will stay 20 to 35 percent.

Winds are still expected to peak Tuesday night into Wednesday
morning. A Particularly Dangerous Situation is expected for inland
Orange County, Santa Ana mountains, Inland Empire, and foothills of
the San Bernardino mountains from 7 am to 1 pm Wednesday due to a
period of widespread strong winds, very dry air, and critically dry
fuels. Widespread gusts of 50 to 65 mph expected on the coastal
slopes of the mountains, below passes, into the Inland Empire,
and inland Orange County. Peak gusts of 45 to 60 mph expected in
San Diego County valleys, with the stronger gusts more localized
to near the mountain foothills. Wind prone locations have the
potential to see gusts exceed 75 mph during the peak of the winds.
Winds look to very slowly weaken and become more localized from
their peak, with gusts 40 to 60 mph still possible into late
Wednesday afternoon. The drier air is expected to become more
widespread Wednesday, reaching into San Diego county and the area
mountains. Relative humidity values on Wednesday are expected to
fall to the 7 to 12 percent for inland Orange County and the
Inland Empire. For San Diego County and the Riverside County
mountains minimum relative humidity will fall to the 15 to 25
percent range with those higher values more likely in the San
Diego County mountains. Winds are expected to be stronger along
the Orange County coast compared to much of the San Diego County
coast. For coastal Orange County max gusts of 45 to 55 mph, with
local gusts to 60 mph during the peak Tuesday night into Wednesday
morning. For coastal San Diego County gusts will peak in the 20
to 35 mph range for the most part. North of Oceanside some gusts
to 45 or 50 mph may occur. Relative humidity near the coast will
be near 15 percent Wednesday afternoon.

There is still some uncertainty surrounding the winds on Thursday.
Much higher confidence in dry air being in place so any elevated
winds will bring critical fire weather conditions. Latest high
resolution guidance indicates a secondary peak in winds Thursday for
the most mountain locations and portions of the Inland Empire. The
strongest winds are currently being depicted on the coastal slopes
of the San Bernardino mountains, below the Cajon Pass, and locally
into the Inland Empire. There is a 60 percent chance of moderate to
locally strong winds continuing into Thursday morning, with higher
chances of more moderate winds continuing. Poor humidity recovery is
expected for Wednesday night into Thursday, especially for the
locations where the winds stay elevated. Minimum relative humidity
for inland areas is expected to fall to the 9 to 15 percent range
Thursday.

Dry conditions will continue into Friday, but there is much lower
confidence in wind speeds at this time. Latest ensemble guidance
indicates a 40 percent chance of moderate winds continuing into
Friday with a 20 percent chance of moderate to locally strong winds
continuing. With the dry air in place, critical fire weather
conditions may continue into Friday for some locations depending on
how the wind forecast develops.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning from 4 AM Tuesday to 6 PM PST Wednesday for
     Orange County Inland Areas-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-Santa Ana Mountains and Foothills.

     Red Flag Warning from 1 PM Tuesday to 6 PM PST Thursday for
     Orange County Inland Areas-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-
     Santa Ana Mountains-Including The Trabuco Ranger District
     of the Cleveland National Forest.

     High Wind Warning from 4 PM Tuesday to 6 PM PST Wednesday for
     Riverside County Mountains-San Diego County Mountains-San
     Diego County Valleys-San Gorgonio Pass Near Banning.

     Red Flag Warning from 4 AM Wednesday to 6 PM PST Thursday for
     Riverside County Mountains-Including The San Jacinto Ranger
     District Of The San Bernardino National Forest-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.

     Wind Advisory from 10 AM Tuesday to 2 PM PST Wednesday for Apple
     and Lucerne Valleys.

     Red Flag Warning from 4 PM Tuesday to 6 PM PST Wednesday for
     Orange County Coastal Areas.

     High Wind Warning from 5 PM Tuesday to 2 PM PST Wednesday for
     Orange County Coastal Areas.

PZ...Small Craft Advisory from 10 AM Tuesday to 1 PM PST Wednesday
     for Coastal Waters from San Mateo Point to the Mexican
     Border and out to 30 nm-Waters from San Mateo Point to the
     Mexican Border Extending 30 to 60 nm out including San
     Clemente Island.


&&

$$

PUBLIC/FIRE WEATHER...CO/APR
AVIATION/MARINE...APR/KWW