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Wx Forecast - Wx Discussion - Wx Aviation

621
FXUS66 KSGX 061740
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1040 AM PDT Mon Apr 6 2026

.SYNOPSIS...
Very patchy fog may develop this Monday morning along the coast.
Low clouds and fog will become more widespread each night and
morning through the week as the marine layer deepens.
Temperatures will fluctuate a few degrees each day through mid-
week, remaining around 5 to 10 degrees above normal. Much cooler
with gusty onshore winds and chances of precipitation late in the
week.

&&

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

...updated Aviation Discussion below...

Widespread high clouds continue to move across the region this
morning. With the thick high cloud cover, coastal fog has
struggled to develop. Expect any fog this morning to remain
sparse. A weak short wave trough moves through today, bringing
widespread cooling for the mountains westward with little change
in the deserts. Weak transitory ridging then follows for Tuesday
and Wednesday. Overall expect minimal day-to-day changes through
Wednesday with highs around 5-10 degrees above normal each day.
Once high clouds move out tonight, marine layer low clouds and fog
will have a better chance of developing across the coastal areas.
With persistent onshore flow the next few days, the marine layer
will become more established with high clouds spreading into the
coastal areas and far western valleys each night.

Ensembles have come into much better agreement with regards to the
progression of an upper level low, which is currently situated
well off the coast of Northern CA. This low will slowly approach
the coast Thursday and Friday, bringing more noticeable cooling
and high temperatures returning to near normal. The approach of
this low will also generate gusty southwest to west winds in the
mountains and deserts, as well as a deeper marine layer with low
clouds extending into the valleys each night. The GEFS remains on
the faster end of the eastward progression of the low, bringing
precipitation as early as Friday morning. However, this only
accounts for about 18% of the total ensemble space. Around 50%
have precipitation by Friday afternoon, but all are showing the
heaviest precipitation occurring Saturday morning through Saturday
evening with light showers lingering into Sunday.

There is still a lot of spread in precipitation amounts, though in
general ensembles have been trending slightly wetter. For the 48
hour period from 4 AM Friday - 4 AM Sunday, the probability of
0.25" or more has increased to 50-70% for the coast to the
mountains, 20-25% for the high desert, and 5-10% for the low
desert. Chances of 0.50" or more range from 20-40% for the coasts
and valleys, 40-60% for the coastal mountain slopes, 10% for the
high desert, and less than 10% for the low desert. Instability
increases Saturday afternoon as the cold core moves overhead,
bringing a 15% chance of thunderstorms. Any thunderstorms that
develop could produce locally heavier rain.

The upper low moves out by late Sunday and weak troughing remains
over the Western US into Monday, maintaining cool weather with
highs a few degrees below normal.

&&

.AVIATION...
061730Z...BKN-OVC high clouds above 15000 feet MSL through 18-20Z,
becoming mostly clear thereafter. Some of these mid level clouds
have become convective enough to produce -SHRA/Virga. Coastal low
clouds more likely after 05Z tonight along the immediate coastlines,
and then spreading into some of the inland valleys by 09-11Z
Tuesday. Bases will be similar to last night, although a little more
elevated at around 1000-1500 ft MSL along the coastal areas, then
falling to around 500 ft further inland with better coverage
expected further inland tonight, with patchy fog being possible for
portions of the inland areas. These clouds should begin to scatter
from east to west by tomorrow morning by 15-17Z Tuesday.

&&

.MARINE...
No hazardous marine conditions are expected through Friday. Wind
gusts in the outer waters could exceed 20 knots Wednesday night.

&&

.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...SS
AVIATION/MARINE...Stewey