380
FXUS66 KSGX 260421
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Tue Jun 25 2024

.SYNOPSIS...
High pressure aloft will weaken as a trough of low pressure builds
over the west coast the rest of this week. Some cooling will occur,
especiaily at night, along with increasing low clouds and fog near
the coast. Hot weather will continue in the deserts through around
Thursday followed by some cooling. High pressure will likely rebuild
early next week and bring renewed warming.

&&

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

Update...

After a couple of sparse nights, stratus has developed along the San
Diego County coast this evening, with mostly clear skies elsewhere.
Only cumulus occurred over the mountains this afternoon as
instability was insufficient for thunderstorms. We still have high
precipitable water values due to continued moisture aloft as NKX had
1.64", though higher clouds were rather rare due to no levels of
near saturation above the marine layer. Overall, minor changes will
occur through Thursday, with the biggest change being gradually
cooler nights as the moist air mass wanes as that upper low develops
over the West Coast and switches our winds aloft from southerly to
westerly, especially starting Wednesday night and Thursday. Already
temperatures are mostly 2 to 6 deg F lower this evening versus 24
hours before mainly west of the mountains as the marine layer
inversion gets stronger and the sea breezes usher in the cooler
marine air. This cooling will be somewhat limited as we got a recent
boost in the sea surface temperatures, which are mostly now in the
upper 60s to lower 70s, including at near-coastal buoys. The
thunderstorm risk will be nil on Wednesday though some cumulus will
still form over the mountains as CAPE and mid-level RH decrease just
slightly. Looking ahead to next week, there is indication that
monsoonal moisture will return sometime around Tuesday, so we will
keep an eye on that.

From Previous Discussion...

Warm conditions will prevail through much of the week. The ridge
to the east weakens slightly by Friday, allowing lower heights
and more zonal flow to come into the region. This will knock
temperatures down a few degrees across the area by Friday, leading
to near average daytime highs. Heat risk will lower as well,
mainly due to overnight temperatures not being as warm with lows
near to a few degrees below normal. Winds will be breezy across
the typical spots in passes into the deserts; most models
indicating winds 20-35 MPH most afternoons and evenings, highest in
the San Gorgonio Pass with gusts near 35-45 MPH. The marine layer
will also become slightly deeper by this time, with greater
coverage of low clouds and fog for areas west of the mountains.

An area of high pressure will grow and expand across the Pacific
by early next week, which will lead to another subtle warm up with
temperatures slightly above average away from the coast. This will
decrease the marine layer depth, leaving low clouds and fog to
occur closer to the coast.

&&

.AVIATION...
260400Z...Coast/Valleys...Visible satellite shows the marine layer
is beginning to build back in with KSAN at BKN015 and KCRQ at BKN010
with tops around 1700ft MSL. The layer will continue to thicken with
lowering CIGs around 08-10z as low as 700ft MSL, scattering out
beginning around 16z. Periods of HZ and reduced VIS possible at KONT
beginning around 16z. Marine layer will build back in with similar
CIGs again Wednesday evening.

Mountains/Deserts...Breezy westerly winds decreasing over the next
few hours, becoming light and variable overnight. FEW150 to FEW250
will prevail through the period, and gusty winds return to most
locations Wednesday afternoon.


&&

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

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 8 PM PDT Thursday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...Maxwell (Update)/APR (Previous Discussion)
AVIATION/MARINE...Zuber