658
FXUS66 KSGX 040341
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
841 PM PDT Thu Oct 3 2024

.SYNOPSIS...
Hot conditions are expected for inland areas into early next week.
Influence from the marine layer will help moderate temperatures
closer to the coast. The marine layer will deepen into Friday, with
low clouds reaching into portions of the western valleys, then become
shallower over the weekend. A gradual cooling trend is expected
for much of next week.

&&

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

Evening update...
The coastal eddy is alive and well this evening with low clouds
already spreading into portions of the western valleys of San
Diego County and inland Orange County. Patchy dense fog is likely
overnight into Friday morning over the higher coastal terrain and
on the coastal mesas. The cumulus clouds that developed over the
mountains this afternoon thanks to some thin mid-level moisture
have since dissipating, leading to clear skies elsewhere. An upper
level trough moving inland across the Pacific Northwest and the
deeper marine layer will help spread some cooling inland, mainly
for the mountains westward, while temperatures in the deserts
remain similar to today. Even with the "cooling", highs will
generally be 10-15 degrees above normal.

Previous discussion...
For Saturday and Sunday, the ridge of high pressure will shift back
to the west becoming more centered over Southern California. Highs
on Saturday are expected to be 3 to 7 degrees warmer than Friday
west of the mountains with minimal changes in the mountains and
deserts. A few additional degrees of warming or no change in high
temperatures is expected on Sunday. Highs will be mostly 15 to 20
degrees above average Saturday and Sunday except for the highest
elevations in the mountains and along the immediate coast. Low
temperatures across the area will remain above average. A shallower
marine layer is expected over the weekend, which will allow for some
warming closer to the coast. A trough of low pressure is forecast to
develop near the California coast early next week. Influence from
the trough will bring a few degrees of cooling for most locations
Monday, with continued cooling into Thursday. There still remains
some uncertainty surrounding the strength of the low through
Thursday with uncertainty in the position of the low starting
Wednesday. The strength and position of the low will ultimately
impact how much cooling occurs. Current forecast has high
temperatures near to slightly above normal by Thursday for the
coastal areas and 5 to 10 degrees above average for the valleys,
mountains, and deserts.


&&

.AVIATION...
040315Z...Coast...Low clouds and fog have resurged inland this
evening. Bases are similar to this morning`s, 400-800 ft MSL, with
tops to 900-1000 ft MSL. These will move slightly further inland
overnight into Friday, locally into western valleys, with vis
reductions 3-6 SM along the coast and 0-3 SM for higher coastal
terrain and elsewhere where terrain intersects with clouds. Clouds
will clear to the immediate coast/beaches 16-18Z Fri morning, but
southerly flow with the coastal eddy will lead to persistent clouds
along the immediate coast for most of the day. Likely some further
clearing will occur in these areas 20-21Z Fri. Southerly winds will
switch to west to northwesterly around 02-04Z Sat as the eddy ends.
This will also lead to the marine layer lowering further, and clouds
that do redevelop 01-03Z Sat may stay largely offshore or along the
immediate coast, with moderate chances of impacts at coastal sites.

Valleys/Mountains/Deserts...Mostly clear skies and unrestricted VIS
persists through Saturday afternoon. SCT CU near 12000 feet MSL Fri
afternoon after 17-18Z, locally BKN at 10000 feet MSL mainly over
mountains until 01Z.

&&

.MARINE...Patchy coastal fog with visibility of 1-3 nautical miles
is possible overnight into late Saturday morning. Otherwise, no
hazardous marine conditions are expected through Tuesday.

&&

.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 Monday for Coachella
     Valley-San Bernardino and Riverside County Valleys-The
     Inland Empire-San Diego County Deserts-San Diego County
     Valleys-San Gorgonio Pass Near Banning-Santa Ana Mountains
     and Foothills.

     Heat Advisory until 8 PM PDT Monday for Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Mountains.

PZ...None.

&&

$$

PUBLIC...SS/CO
AVIATION/MARINE...CSP