890
FXUS66 KSGX 052107
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
207 PM PDT Sat Oct 5 2024

SYNOPSIS...
Upper ridge is now over southern California and will bring
hot conditions for inland areas through Monday with daytime highs
much above normal. Below this heat dome a widespread shallow marine
layer exists along the coast. A weak Pacific weather system will
arrive by Tuesday and lead to a deeper marine layer and overall
cooler conditions for all areas. The temperatures in the inland
valleys, deserts and mountains will continue to be 5 to 10 degrees
above averages.

&&

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

Marine clouds cleared to beaches by 10 am but then sea breeze
pushed back more to the beaches and near I-5. Marine layer is
slightly lower today but widespread with tops 1200-1400 feet MSL.
A new clearing area is forming over northern Orange County from
Long Beach land area and a new Catalina Eddy is also evident. The
upper ridge of 592 DM 500 mb heights is now centered directly
over Socal, so air mass is a little warmer with 26 to 29C at 850
mb level. Clearing will likely hold at the beaches again on Sunday
due to strong inversion but breaks into Orange County and parts
of San Diego coastline.

Upper heights start to lower on Sunday but similar air mass
in place. On Monday with the approach of a weak upper trough from
the Pacific, there is cooling of 1C aloft along the coast and
marine layer should also start to deepen. Inland for the deserts
there is little change with 29C at 850 mb in place. By Tuesday
air mass lowers to 22-23C at 850 mb on the coast and 26-27C
for desert with notably increase to southwest flow aloft.

Despite synoptic cooling on Tuesday and Wednesday, inland valleys
to deserts still are 5 to 10F above averages.

There is a more significant upper trough from the Pacific for late
next week, that would return temperatures to near averages by
Friday and into Saturday. However, this system is forecast to
close off over the Great Basin or Desert Southwest and could
bring some offshore flow in its wake and return to above normal
temperatures by next Sunday and Monday.

&&

.AVIATION...
052030Z...Coasts/Far Western Valleys...Stratus with bases 400-800 ft
MSL and tops to 900-1200 ft MSL cleared out to the beaches earlier
this morning, but have since nudged back onshore a few miles with
the sea breeze. The edge of the clouds could dance a mile east/west
through the afternoon before solidly pushing 5-10mi inland after
00z. Cloud bases should lower to 200-500ft MSL by 12z. Areas of VIS
1-3SM this afternoon and evening become 0-2SM for 09-16z. Clouds and
fog look to clear back to the beaches once again around 18z Sunday
morning, likely nudging a few miles back onshore again for the late
morning/early afternoon with the sea breeze.

Valleys/Mountains/Deserts...SCT and locally BKN cumulus with bases
12000-15000 feet MSL over the mountain crests until 01Z this
afternoon. Otherwise, mostly clear skies with unrestricted VIS
expected through Sunday afternoon.

&&

.MARINE...Visibility locally reduced to around 1-3 nm in fog/haze
likely through the afternoon and evening hours, especially for the
nearshore waters. Higher confidence fog with visibility down to 1 nm
or less along the nearshore waters for late tonight, persisting
through Sunday afternoon and into late Monday morning. Otherwise, no
hazardous marine conditions are expected through Thursday.

&&

.FIRE WEATHER...
Elevated fire weather conditions due to the lower daytime
humidity, poor recovery at night above the marine layer and
conditions hot daytime temperatures which are 10 to 20 degrees
above averages. Southwest flow increases on Tuesday, up to 20
knots at 850 mb level. Fuels are very dry and stressed from
the heat wave and summer with limited monsoon.

&&

.CLIMATE...
Inland valleys, foothills, mountains and deserts will be 10 to 20
degrees above 30 year averages for Saturday to Monday. This brings
the potential for additional records. Ramona normal high is 82F
and the record on Sunday is 98F for example. Palm Springs average
high is 92F and a forecast of 111F is 19F above average and at
the record level. The mountains are the same with Palomar mountain
normal of 72F and a forecast of 89F. For the Inland Empire, Lake
Elsinore average high is 86-87F and forecast and record is
103-105F.

Palm Springs on pace to be warmest first week to October with
average temperature of 96F.

&&

.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/FIRE WEATHER...Tardy
AVIATION/MARINE...Munyan