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972
FXUS66 KSGX 191051
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
351 AM PDT Thu Sep 19 2024

.SYNOPSIS...
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A low pressure system moving across southern California will
deepen the marine layer and maintain well-below average high
temperatures through Friday with chances for showers for late
tonight through Friday afternoon along with a slight chance of
thunderstorms for Friday afternoon. Then dry and much warmer for
the weekend into next week with high temperatures warming to a few
degrees above average on Sunday and 4 to 8 degrees above average
for inland areas for Monday through Wednesday.
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&&

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

.SHORT TERM (Today through Saturday)...
The center of a closed low pressure system is moving southward off
the coast of central California early this morning. The center is
expected to move to near Point Conception for late this afternoon
and across southern California during the day on Friday, then
weakening as it moves into Arizona Friday night and into Colorado
on Saturday.

The marine layer has deepened to around 4000 feet. However, cloud
bases have also risen with the depth of the cloud layer around
1000 to 1500 feet with some holes in the coverage. High
temperatures will be a few degrees cooler today for the mountains,
inland valleys, and high desert with high temperatures for today
for the mountains and inland valleys around 15 degrees below
average.

Chances for light precipitation today will be mostly 10 percent or
less and greatest over the coastal waters this morning. The
greater chances for showers are for late tonight through Friday
afternoon. The HREF shows the potential for island band showers
to develop and move into San Diego County from the coast to the
mountains for late tonight into Friday morning. During the late
morning and afternoon on Friday, moisture in the cyclonic
circulation around the upper low could bring showers from the
northeast along with a slight chance of thunderstorms for the
mountains, deserts, and inland valleys of southwestern San
Bernardino and western Riverside Counties. NBM has increased
chances for measurable rainfall at Big Bear to 57 percent on
Friday with a 19 percent chance for one-quarter inch or more of
rainfall.

Slightly cooler high temperatures are expected for inland areas on
Friday, then a few degrees warmer on Saturday near the coast to as
much as 10 to 15 degrees warmer for the mountains. Even with the
warming, Saturday high temperatures will still be a few degrees
below average to as much as 5 to 10 degrees below average for the
valleys.
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&&

.LONG TERM (Sunday through Wednesday)...
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For Sunday and Monday, low pressure will weaken with generally
northwest flow aloft across the area. By Tuesday and Wednesday,
a blocking pattern may develop across the western states.

Dry weather is expected for Sunday through Wednesday. High
temperatures are expected to warm several degrees for Sunday and
Monday with Sunday high temperatures a few to around 5 degrees
above average for inland areas and around 4 to 8 degrees above
average for inland areas for Monday through Wednesday.

With the warming, high temperatures for the Inland Empire on
Sunday would be mostly in the upper 80s to mid 90s and mostly in
the 90s for Monday through Wednesday. NBM shows greater spread in
the high temperature guidance for the middle and latter part of
next week with the greatest spread for the coast and valleys.
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&&

.AVIATION...
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190930Z...Coast to mountain slopes...Low clouds fill the entire
coastal basin this morning. Bases will be 2500-3000 feet MSL, with
tops 3500-4000 feet. Areas of higher terrain between those levels
obscured. Scatter out for many areas should occur 16-19Z, but BKN
clouds could linger or regenerate, but probably based around 3500
feet MSL. Low clouds to eventually fill the entire coastal basin
again 01-09Z into Friday with similar bases/tops. Patchy -RA or -DZ
most likely along the coast and up against the coastal mountain
slopes after 06Z Friday, which would reduce vis.

Mountain ridges to deserts... SCT high clouds today and tonight.
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&&

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

&&

.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...17
AVIATION/MARINE...MM