260
FXUS66 KSGX 011647
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
947 AM PDT Tue Oct 1 2024

.SYNOPSIS...
Hot conditions with well above average temperatures are expected
through into early next week for inland areas. A shallow marine
layer will help moderate temperatures at the coast. Night and
morning low clouds and fog are expected at the coast most mornings.
For Thursday and Friday the marine layer may deepen enough to
reach into the western valleys at times, before becoming shallower
again over the weekend.

&&

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

Visibilities this morning were lowest closer to the coast and along
the I-5 corridor. A Dense Fog Advisory was issued for Orange
County through 10 AM. Visibility fell to a quarter of a mile for
Fullerton and Los Alamitos overnight. Lifeguard observations for
Newport Beach had visibility at 1 mile at 7 AM. Visibility will
continue to improve this morning for most locations. A strong
inversion on the 12Z KNKX sounding indicates that low clouds and
areas of fog may linger along the immediate coast into the
afternoon. Areas of dense fog are possible again tonight into
Wednesday morning. HREF guidance has 60 percent chance of
visibility 1 mile or less over the coastal waters and at the
beaches overnight.

High pressure will remain parked over California through Thursday
before the ridge axis shifts east into the Great Basin area on
Friday. This will bring well above average temperatures to the area
for the middle of the week. High temperatures are expected to be 10
to 15, locally up to 20, degrees above average for inland areas.
This will bring widespread major to extreme HeatRisk to the valleys
and mountains, with moderate to locally major HeatRisk in the
mountains. Overnight low temperatures will remain elevated
preventing significant overnight relief from the heat, especially in
the mountains, foothills, and deserts. The development of a coastal
eddy late Wednesday into Thursday and the eastward shift of the
ridge axis on Friday should allow the marine layer to deepen
slightly, reaching into portions of the western valleys. With a
deeper marine layer high temperatures in some locations west of the
mountains have the potential to cool a few degrees for Thursday and
Friday. Even with a few degrees of cooling, highs will remain well
above average.

The ridge of high pressure will move west to be back over California
for Saturday and Sunday. This will bring another round of warming
conditions for the weekend. The weekend warming may bring warmer
conditions to coastal areas with high temperatures on Saturday 5 to
10 degrees above average near the coast. The inland valleys will
remain quite warm with highs 15 to 20 degrees above average. That
will put high temperatures around 80 near the coast to 100 to 105
for the inland valleys. Not much change for the mountains and
deserts over the weekend with high temperatures mostly 10 to 15
degrees above average, around 110 for the lower deserts.

Near record high temperatures are possible for the mountains, lower
deserts, and inland valleys through Sunday. Several locations for
the mountains, lower deserts, and valleys could have record warm
overnight low temperatures each night through the weekend. Some
mountain locations could break the existing records by several
degrees.

For early next week, most ensemble guidance keeps some degree of
ridging over the area although there are some indications the ridge
may weaken. Current forecast has a gradual cooling trend for Monday
and Tuesday, but high temperatures will remain 10 to 15 degrees
above average for inland locations.

&&

.AVIATION...
011630Z...Coast...Low clouds with bases 200-600 feet MSL, tops to
900 feet and vis 1-5SM should finish scattering out to the beaches
over the next 30-60 minutes. Some clouds may linger along/just
offshore for the next few hours before clearing. Low clouds and fog
to redevelop after 03Z tonight with similar bases/tops and VIS
restrictions. Clearing/scattering expected around 16-17z Wednesday
morning.

Valleys/Mountains/Deserts...Mostly clear skies today and tonight.
Locally reduced vis in FU around the Line Fire in the San Bernardino
Mountains.

&&

.MARINE...Any clouds and the fog remaining over the waters
should continue to lift/clear as we move into the late morning
hours. Patchy dense fog is possible again tonight into Wednesday
morning. Otherwise, no hazardous marine conditions are expected
through Saturday.

&&

.FIRE WEATHER...
High pressure over the eastern Pacific will expand across California
with much warm weather. The hottest days for the valleys into the
coastal areas are expected for today and Wednesday with today the
hottest day for the lower deserts. A weak coastal eddy could bring a
few degrees of cooling for the coast and valleys for Thursday and
Friday.

The lowest daytime humidity for the mountains and deserts will fall
to 10 to 15 percent for each afternoon through the weekend.
The humidity for the inland valleys will also fall to 10 to 15
percent for this afternoon and Wednesday afternoon and again for
Saturday and Sunday afternoons. A weak coastal eddy may bring a
slightly recovery in humidity for the valleys on Thursday and
Friday.

&&

.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 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 Thursday for Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Mountains.

     Dense Fog Advisory until 10 AM PDT this morning for Orange
     County Coastal Areas-Orange County Inland Areas.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...CO/17
AVIATION/MARINE...Munyan