919
FXUS66 KSGX 222148
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
148 PM PST Wed Jan 22 2025

.SYNOPSIS...
Critical fire weather conditions continue as Santa Ana winds and dry
conditions continue into early Friday. Strongest winds are expected
on Thursday. Single digit afternoon relative humidity values will
occur through Friday afternoon. Shift in the weather is expected
for the weekend, with increasing chances of rain and mountain
snow. Some showers could linger into early next week.

&&

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

Through tonight there will be northeast winds of 20 to 30 mph with
gusts to 45 to 55 mph along and below the coastal slopes of the
mountains. Winds will increase for Thursday, with northeast winds of
30 to 40 mph with gusts to 60 to 75 mph and with isolated gusts to
85 mph for the San Diego County mountains. Winds will slowly
decrease into Friday morning. Overnight humidity recovery will be
poor Thursday night into Friday, with relative humidity only
reaching 15 to 20 percent for inland locations. Lowest daytime
humidity will fall to around 5 percent Thursday afternoon and
around 5 to 10 percent on Friday afternoon. A few degrees of
cooling is expected for Thursday away from the coast. Then cooler
on Friday for coastal areas with the mountains a few degrees
warmer.

An upper level low pressure system from the north will move into
central California on Saturday. The low will slowly move southward
into Southern California by Sunday or Monday. Most of the
uncertainty in the model ensemble solutions surrounds the timing of
the low, with lesser uncertainty in the amplitude of the low. Most
of the ensemble solutions for Sunday and Monday (80 and 75 percent
respectively) keep the low more to the west which would be a
favorable track for precipitation across the area. Current forecast
keep precipitation chances through Tuesday. Through Tuesday night
there is a 50 to 70 percent chance of one-quarter inch or more of
precipitation for the coast and valleys, with an 80 percent chance
of one-quarter inch or more of rainfall/liquid-equivalent in the
mountains. In the mountains there is a 30 to 40 percent chance for
three-quarters of an inch or more of rainfall/liquid-equivalent. Current
forecast has the highest and most widespread chances of rain
Saturday night into Sunday.

This is expected to be a cold system with snow level of 4000 to 5000
feet on Saturday afternoon will fall to around 3500 to 4000 feet on
Sunday. Current forecast keeps the snow level 3500 to 4000 feet
through Tuesday. Ensemble guidance is indicating that snow could
accumulate in the High Desert, with multiple members of both the
ECMWF and GFS showing some amount of accumulating snow although
there is a wide range of solutions when it comes to how much snow
will accumulate. NBM chances for 12 inches or more of snowfall in
the mountains for the weekend is around 80 percent for elevations
above 7000 feet.

There remains uncertainty in the forecast for early next week.
Much of the uncertainty surrounds the timing of how quickly the
low pressure system will depart to the east. Due to the cold
nature of the system, below average temperatures are forecast for
Saturday through Wednesday. By Wednesday most ensemble solutions
have the low to our east with a ridge of high pressure building
over the West Coast of the US.

&&

.AVIATION...
222100Z....SCT-BKN high clouds will continue today and tonight.
Areas of northeast winds 25-35 kts mainly in foothills and adjacent
valleys will continue today and tonight, generating pockets of LLWS
and mod up/downdrafts in lee of mountains. East to northeast winds
strengthen and become more widespread early Thursday morning,
peaking early Thursday afternoon with gusts 30-45 kts, locally
stronger in foothills and adjacent valleys, before gradually
subsiding through Thursday night.

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...
Offshore winds become breezy late tonight through Thursday. There is
a slight chance of thunderstorms late Saturday associated with a
regional storm system. Any thunderstorms could produce locally
gusty, erratic winds and briefly hazardous conditions. Otherwise,
prevailing winds and seas are not expected to generate hazardous
marine conditions through Sunday.

&&

.FIRE WEATHER...
Critical fire weather conditions will continue through Friday
morning. The strongest winds are expected during the day on Thursday
with northeast winds of 30 to 40 mph with gusts to 60 to 75 mph and
isolated gusts to 85 mph for the San Diego County mountains. Lowest
daytime humidity will fall to around 5 percent Thursday and around 5
to 10 percent on Friday with poor overnight recovery.

Substantial recovery in humidity is expected during the weekend with
widespread wetting rain and mountain snow.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 10 AM PST Friday 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.

     High Wind Warning from 6 AM to 6 PM PST Thursday for Orange
     County Inland Areas-Riverside County Mountains-San
     Bernardino County Mountains-San Bernardino and Riverside
     County Valleys-The Inland Empire-San Diego County Mountains-
     San Diego County Valleys-San Gorgonio Pass Near Banning-
     Santa Ana Mountains and Foothills.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...CO
AVIATION/MARINE...CSP