278
FXUS66 KSGX 192103
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
103 PM PST Fri Dec 19 2025
.SYNOPSIS...
High pressure will begin to weaken over the area into the weekend,
which will continue to provide warm conditions. Patchy fog will
continue near the coast and western valleys into early next week.
An area of low pressure will push an atmospheric river over the
region around the Christmas holiday, where there is an increased
risk of heavy rain and flooding. The area of low pressure may
stick around into the latter next week, leading to more chances
for rain and high elevation snow.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
...Previous Discussion (1029 AM Friday)...
A 1023mb area of high pressure to the southwest will continue to
dominate our weather pattern through the weekend. Visible
satellite shows dense fog persistent over the waters and parts of
the coastline this morning. Intermittent fog will continue
throughout the day near the beaches before clouds move around 5-10
miles inland where the foggiest conditions will occur on elevated
coastal terrain. As the ridge of high pressure slowly breaks
down, a slight increase in onshore flow will occur, cooling the
coast and valleys a few degrees from yesterday. The mountains and
deserts will see similar temperatures with highs in the 70s/80s
across the deserts. The cooling will slowly continue into the
weekend and Monday as the marine layer deepens, though highs will
remain above average. Highs will be 5-10 degrees above normal west
of the mountains and 10-15 degrees above normal in the mountains
and deserts.
Two features to the north will lead to a big change in the weather
as we head into the Christmas holiday. An atmospheric river seen
from the Hawaiian Islands into Northern California and an area of
low pressure over the eastern Gulf of Alaska will begin to push
southward by Monday and Tuesday of next week. The trough of low
pressure will aid to push the atmospheric river southward,
orienting the system in a more north/south direction. This will
first provide heavy rain to parts of the Central Coast late Monday
night into Tuesday and push southward into our region late Tuesday
into Wednesday. As a series of shortwaves pass the trough`s axis,
rapid deepening of the low will occur. Confidence on timing
continues to increase with the heaviest rain falling from the
atmospheric river on Wednesday (Christmas Eve Day). The wind
forecast has increased as models show higher chances for wind
gusts mainly across the immediate coast and mountain areas to gust
over 30 MPH at times as the AR passes by on Wednesday.
A secondary shortwave in the trough may provide another moderate
to heavier round of precipitation on Christmas Day. The track
of the large low pressure system still remains uncertain. Some
models show a slower moving system, which would give us more
chances of rain into next weekend, while others show a faster and
not as wet solution. Model ensemble trends show a slight increase
over the past few days, so rain chances continue into the forecast
for later next week.
&&
.AVIATION...
192100Z...Coast/Western Valleys...Low clouds and fog will gather at
the coast this afternoon and spread inland after 01Z, eventually
into western valleys overnight. Bases 300-500 feet MSL with vis 0-
5SM, lowest on coastal mesas, higher coastal terrain, and western
valleys. Scatter out Saturday 17-19Z.
Otherwise...FEW-SCT high clouds with unrestricted VIS through
Saturday morning.
&&
.MARINE...
Areas of fog with reduced visibility below 1 nautical mile through
Saturday morning. Following that, no hazardous marine conditions are
expected through Tuesday morning. Increasing south winds develop
late Tuesday in advance of a Pacific storm. Conditions could become
hazardous to small craft Tuesday night through Wednesday.
&&
.HYDROLOGY...
For Wednesday morning through Wednesday night for Lytle Creek on
the coastal slopes of the eastern San Gabriel Mountains, the
chance for 3 inches or more of rainfall has increased to 71
percent with a 35 percent chance for 5 inches or more and an 11
percent chance for 6 inches or more. For Wednesday morning through
Thursday night, the chance for 8 inches or more of rainfall at
Lytle Creek has increased to 13 percent. Chances for heavy
rainfall continue to increase as model trends go upward.
Probabilities for seeing rainfall totals over 2 inches Tuesday
through Thursday night are listed below:
- OC/IE: 60-90% chance
- SD Co Mts/Coast/Valleys: 45-75% chance
- Deserts: 15%-25% (lower deserts), 40-55% chance (high desert)
Probabilities for seeing rainfall totals over 3 inches Tuesday
through Thursday night are listed below:
- OC/IE: 50-70% chance, 25-35% chance (eastern IE)
- SD Co Mts/Coast/Valleys: 20-50% chance
- Deserts: 5%-10% (lower deserts), 15-25% chance (high desert)
NBM deterministic rainfall for next week through Thursday night
for northern Orange and southwestern San Bernardino Counties
ranges from 3.5 to 4 inches near the coast to 6 to 9 inches on the
coastal slopes of the mountains to the west of the Cajon Pass.
Amounts decrease to the south to 1.5 to 2 inches near the coast of
central and southern San Diego County to 2 to 3 inches for the
mountains of central and southern San Diego County. For the high
desert, 2 to 3 inches is expected with 0.5 to 1.5 inches for the
lower deserts.
Most of the precipitation across southwestern California through
Christmas Thursday is expected to fall as rain with snow levels
remaining above 7000 feet. Snow levels will drop some by later
next week, but exact levels and locations remains uncertain.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
PUBLIC...APR
AVIATION/MARINE...MM
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