Winter Storm Warning 1, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
1006 AM PST Fri Jan 24 2025

.SYNOPSIS... Winds will weaken during the day, but conditions will
stay very dry with single digit relative humidity. For the weekend
into early next week, a cold low pressure system from the north is
expected to bring cooling with widespread showers and mountain snow
for Saturday night through Tuesday. Dry and warmer weather is
expected for the remainder of the week.

&&

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

.Morning Update...

East winds are beginning to weaken this morning with gusts 20-35
MPH. Though the air remains very dry with single digit relative
humidity values, fire weather risk will lower by the afternoon
hours. GOES imagery shows higher level clouds coming up from the
south with some areas in San Diego County seeing smoke from the fire
on Otay Mountain and in northern Baja, so expect hazy conditions
throughout the day. Onshore winds will take hold into Saturday, with
some stiff south winds near the coast. Confidence remains low to
moderate on exact wind speeds, but windy conditions will be
present from the desert mountain slopes into the deserts. ECMWF
ensembles range from peak gusts 35-55 MPH near Victorville by
Saturday afternoon.

Latest hi-res guidance brings in precipitation to parts of Orange
County and the Inland Empire by Saturday evening with precip moving
eastward across SoCal overnight. We continue to work on the forecast
totals for this system as the event lasts through early next week.
Chances for rain/mountain snow begin to drop off by later into
Tuesday, with dry weather expected for the remainder of next week.

.Previous Discussion (415 AM Friday)...

.SHORT TERM (Today through Sunday)...
A return of onshore flow will spread higher coastal humidity
inland beginning later today through the weekend. Stronger onshore
flow will bring stronger and gusty southwest to west winds for
the mountains and deserts for Saturday afternoon through Saturday
night with gusts to 45 to 55 mph and isolated gusts to 70 mph.

Not much has changed with the timing and track of the closed low
pressure system from the north for the weekend into early next week.
The center of that closed upper level low pressure system is
expected to move to near Point Conception late in the day Sunday,
then move slowly eastward across southern California on Monday.
There will be increasing chances for showers on Saturday night into
Sunday. The snow level will rise to around 4500 feet for Saturday
night and around 5000 feet on Sunday.

High temperatures today will be 5 to 10 degrees warmer for the
mountains with coastal areas into the western valleys 4 to 8 degrees
cooler. Cooling will continue to spread inland over the weekend with
high temperatures for Sunday for the coast and valleys mostly in the
50s.

The HRRR smoke output shows smoke aloft spreading northward across
much of San Diego County by this evening with much of that smoke
originating from fires in northern Baja. Near-surface smoke is most
likely across southern portions of San Diego County today.

&&

.LONG TERM (Monday through Thursday)...
Numerous showers will continue into Monday with the center of closed
upper level low pressure system over southern California with the
showers decreasing on Tuesday as the low pressure system moves
slowly eastward. The snow level will fall to around 4000 to 4500
feet for Sunday night and Monday.

NBM probabilities of receiving one inch or more of rainfall/liquid-
equivalent through Monday night are generally 80 to 90 percent from
the coast to the mountains with an 80 percent or greater chance for
three inches or more of rainfall/liquid-equivalent for the typically
wetter mountain locations. For the mountains, there is a 70 percent
chance of receiving 12 inches or more of snowfall above 6000 feet.

&&

.AVIATION...
241700Z....Mostly clear skies with gradually increasing high clouds.
Elevated east-northeast winds in the foothills continue to gradually
taper off by 19-21z. Onshore flow is established this afternoon with
light winds overnight.

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...
There is a slight chance of thunderstorms Sunday evening, any of
which could produce locally gusty and erratic winds, lightning, and
briefly hazardous conditions. Otherwise, prevailing winds and seas
are not expected to generate hazardous marine conditions today
through Tuesday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Watch from Saturday evening through Tuesday morning
     for San Bernardino County Mountains.

     Winter Storm Watch from Sunday morning through Tuesday morning
     for Riverside County Mountains-San Diego County Mountains.

PZ...None.

&&

UPDATE...APR
PUBLIC...17
AVIATION/MARINE...Munyan

Preliminary Local Storm Report
National Weather Service San Diego CA
921 AM PST Fri Jan 24 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0230 PM     Wildfire         5 WSW Dulzura           32.60N 116.84W
01/23/2025                   San Diego          CA   Fire Dept/Rescue

            Border2 wildfire on Otay mountain. 4300
            acres and 10 percent contained. Evacuation
            warnings in effect to the west. Otay
            mountain SDGE had relative humidity 8
            percent and Santa Ana east wind gusts to 35
            to 45 mph at start and through overnight
            hours. Humidity decreased to 3 to 5 percent
            overnight and Friday morning with wind gusts
            to 25 mph.

&&

SGX

Preliminary Local Storm Report
National Weather Service San Diego CA
924 AM PST Fri Jan 24 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0242 PM     Wildfire         5 NNE Mission Beach     32.86N 117.24W
01/23/2025                   San Diego          CA   Fire Dept/Rescue

            Gilman brush fire burned 2 acres. Gilman
            Drive and Via Alicante, South of La Jolla.
            Relative humidity was 6 percent and Santa
            Ana wind gusts 15 to 20 mph at nearest
            weather station. Dewpoint temperature as low
            as -9F overnight.

&&

SGX

Preliminary Local Storm Report
National Weather Service San Diego CA
958 AM PST Fri Jan 24 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0440 PM     Wildfire         3 S Hemet               33.70N 116.97W
01/23/2025                   Riverside          CA   Fire Dept/Rescue

            Gibbel brush fire reached 15 acres. State
            Street and Gibbel Road, Hemet. SCE Heshmet
            had relative humidity at 7 percent and wind
            gusts 15 mph.

&&

SGX