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000
FXUS66 KSGX 120359
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
859 PM PDT Thu Apr 11 2024

.SYNOPSIS...
Warm today before a cooling trend sets in on Friday. Chances of
light showers develop this weekend, with the first round occurring
on Saturday, and the second round occurring on Sunday. Light
accumulations are generally expected. Periods of gusty winds will
occur over the mountains and desert accompanying the rounds of
rain. Dry, but cool, weather returns for next week.

&&

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

9 PM Update: The 00z Miramar sounding showed a low-level inversion
based around 900 FT MSL, about 7-8C strong. The strength of this
inversion is the culprit for the marine layer low clouds hanging
around for much of the day, and also why the current cloud cover
is expected to expand overnight. Cloud bases, per surface
observations, currently range from 400-1000 FT MSL. This would
suggest some areas of fog are possible overnight, namely on
coastal mesas and in some western portions of the coastal valleys.
Trends will be monitored for a potential Dense Fog Advisory
issuance. Aside from the concerns for fog overnight, the forecast
generally looks on track for this weekend’s light precipitation
and gusty winds, so no changes appear necessary this evening.

From Previous Discussion:

At 2 PM, locally dense fog is clinging to the beaches, but
elsewhere, skies are crystal clear. It`s already a warm day out
there; current temperatures are in the mid-90s across the lower
deserts, and the low to mid-80s in the valleys. Today will likely
be the warmest day of the week away from the immediate coast, with
highs topping out 8-12 degrees above normal.

A strengthening closed low is forming to our southwest and another
upper low is quickly moving down the coast of British Columbia and
the Pacific Northwest. The upper low becomes absorbed into the
mean flow and moves over Southern California on Friday. This will
deepen the marine layer, strengthen onshore flow and spread
cooling inland. The cooling trend continues through this weekend,
with Sunday likely being the coldest day of the week, when highs
will top out up to 5 degrees below normal at the coast, and 10-20
degrees below normal across inland areas.

Multiple shortwaves look to pass over the region this weekend, the
first leading to showers on Saturday. Isolated showers could start
as early as late Friday night, but higher chances will exist
during the daytime hours on Saturday. This first round looks
fairly moisture starved and fast moving, so brief heavy showers
will be possible, but overall rain amounts look to remain light.
The second round develops on Sunday as the upper low elongates and
weakens, and looks to retain even less moisture than the first
round. Total rainfall for this weekend looks to range from a few
hundredths of an inch up to a quarter of an inch across the coast
and valleys, generally less than 0.10" in the High Desert, trace
amounts if any in the lower deserts, and 0.10-0.50" in the
mountains, with isolated higher amounts in San Bernardino County.
Snow levels look to remain around 5500-6500 feet for the first
round on Saturday before falling as low as 4500-5500 feet on
Sunday.

Gusty winds over the mountains and deserts will occur this weekend
as well, peaking Saturday afternoon and evening with peak gusts of
40-55 mph. A second, weaker round will occur Sunday afternoon and
evening.

The low quickly moves eastward on Monday, and weak mean flow
sticks around for Monday and Tuesday before longwave troughing
takes hold of the West Coast next week. Subtle warming is expected
each day, but highs look to remain below normal through next week.

&&

.AVIATION...
120400Z...Coast/Valleys...Low clouds will increase in coverage and
spread inland tonight, reaching into portions of the inland valleys
into Friday morning. Bases should be 1200-1600 feet MSL with vis 0-
5SM where clouds and terrain intersect.

Elsewhere...mostly clear skies today and tonight.

&&

.MARINE...
No hazardous marine conditions are expected through Monday. A weak
weather system will bring stronger breezes Friday and Saturday, and
occasional showers Saturday through Sunday, but no hazardous marine
conditions are anticipated.

&&

.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...Adams (Update)/EA
AVIATION/MARINE...Suk