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000
FXUS66 KSGX 210429
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
929 PM PDT Sat Apr 20 2024

.SYNOPSIS...
High pressure across the region will warm things up across the
region through Monday. Night and morning low clouds and fog will
occur west of the mountains, staying closer to the coast the next
few mornings. An area of low pressure off the coast will begin to
impact the region by Tuesday into the end of next week, leading to
cooler, breezier and potentially wetter weather.

&&

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

Low clouds have returned to the San Diego County coastal areas
this evening. The 00Z KNKX sounding shows the marine inversion
base near 1,800 ft MSL, down significantly from the near 3,000 ft
this morning. Low clouds will extend into the western valleys
overnight, but elsewhere skies will remain mostly clear. Breezy
winds through the mountain passes and locally into the deserts
will diminish overnight.

The upper level ridge axis is currently near the Central
California coast and will progress eastward into Sunday. This will
bring a continued warming trend with the marine layer becoming
more shallow. Highs on Sunday will reach the upper 80s to around
90 in the inland valleys and high deserts, and upper 90s to around
100 in the low deserts. This could be the first 100 degree day at
Palm Springs so far this year, though they were close with a high
of 98 degrees twice already this month. The upper ridge is pushed
further east on Tuesday in response to an upper level trough
beginning to amplify over the East Pac. Stronger onshore flow will
help spread cooling inland on Monday, most notably for the
mountains westward, while the deserts only cool by a degree or
two.

The trough begins to split with a closed low eventually forming in
the base of the trough sometime late Monday into Tuesday while
gradually progressing eastward, bringing continued cooling and
gusty southwest to west winds in the mountains and deserts.
Ensembles really begin to diverge in the evolution of this low as
we head into the latter half of the week, with the GEFS and it`s
deterministic counterpart on the much faster end of the guidance,
bringing the main trough axis through by Wednesday evening or so,
while the EPS and Canadian Ens don`t bring it through until
Thursday morning. Either way, this will continue the cooling
trend, but the timing will have implications on the potential for
any (very light) precipitation. Right now the moisture with this
first wave is somewhat limited and the trough is so amplified that
the vort max actually passes to our south. Ensembles are all
showing only trace amounts of precipitation, so this could well
be a marine layer drizzle situation. Winds will continue to
strengthen, but not substantially so with the weaker flow aloft as
the core of the low moves overhead.

The first trough quickly kicks out by late Thursday with cyclonic
flow and cool weather remaining into Friday. Another more potent
trough drops down from the northwest by the weekend, continuing
cool and breezy weather. This second wave is forecast to have
deeper moisture associated with it for a better (20-30%) chance of
precipitation sometime Friday into Saturday, though slight (15%)
chances may begin as early as Thursday evening. Enjoy the couple
days of warm weather we have now, because highs will be back to
around 5 to as much as 15 degrees below normal for Wednesday
through Saturday.


&&

.AVIATION...
210335Z...Coast/Valleys...Low clouds moving into coastal San Diego
County at this hour, with bases around 1500 ft MSL and tops around
1900 ft MSL. Low clouds will spread 15-20 miles inland by 15Z. Bases
will lower overnight and could go below 1000 ft MSL in some areas
between 10Z and 16Z. CIG and VIS impacts expected at coastal TAF
sites but about a 30 percent chance at KONT after 11Z and less than
10 percent chance at KSBD. Expect clearing to the coast 17Z-19Z with
clouds persisting at the beaches into Sun afternoon.

Mountains/Deserts...Mostly clear skies with unrestricted VIS through
Sun morning.

&&

.MARINE...
No hazardous marine conditions are expected through Wednesday.

&&

.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...PG