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639
FXUS66 KSGX 210354
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
854 PM PDT Mon May 20 2024

.SYNOPSIS...
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A large-scale trough over western North America will persist
through this week. Temperatures will remain below seasonal
averages with gusty winds across the mountains and deserts. Low
clouds will continue nights and mornings, retreating back to the
coast each afternoon.
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&&

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

Low clouds are rapidly developing across the coastal areas and
valleys and even into the mountains this evening. The 00Z KNKX
sounding shows the marine inversion based roughly near 3000 ft
MSL, but based on the location of cloud development along the
coastal slopes it appears to be closer to 5000-5500 ft inland.
Breezy west winds with gusts mostly 25-45 mph continue across
portions of the mountains and deserts and will persist tonight,
gradually weakening into Tuesday morning.

The upper level short wave trough continues to move east on
Tuesday with a weaker long wave trough remaining across the
Western US. Despite the troughing, minor height rises and some
decrease in onshore flow will allow for some warming inland,
weaker winds in the mountains and deserts, and a shallower marine
layer Tuesday and Wednesday. Wednesday will be the warmest day of
the week, though highs remain around 2-6 degrees below normal for
the coasts to the mountains, and right around normal in the
deserts.

Upper level troughing will dominate through the end of the week
with an occasional short wave passing through the mean flow. The
trough becomes more amplified Friday with a short wave trough axis
moving through on Saturday. This will bring gradual cooling across
the area for the second half of the week with highs returning to
around 5 to as much as 15 degrees below normal, with the greatest
departure in the valleys and mountains. The marine layer will be
deeper again with clouds extending into the valleys and even the
lower coastal mountain slopes and limited clearing along the coast
each day. Gusty west winds will increase across the mountains and
deserts each afternoon into the late night Thursday through
Saturday as well. The main trough finally shifts east on Sunday
with an upper level high over Mexico beginning to move westward
and amplify into early next week, bringing some warming and less
marine layer cloud cover for Sunday and Monday.
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&&

.AVIATION...
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210330Z...Coast/Valleys...Areas of BKN/OVC low clouds will occur
overnight with bases 1500-2500 ft MSL and variable tops 2500-5500 ft
MSL with areas of terrain obscurations. Local VIS 3-5 miles will
occur in the valleys 07Z-17Z Tue in BR. Clearing will occur in most
areas 15Z-19Z Tue, even though some TEMPO SCT conditions will occur
09Z-15Z Tue. Areas of low clouds will develop again Tue evening near
the coast.

Mountains/Deserts...Areas of terrain obscurations in clouds
will occur on the coastal mountain slopes below 5500 feet through
15Z Tue. Areas of westerly winds with gusts 25-40 kt will continue
through 14Z Tue along the mountain crests, desert slopes, through
mountain passes and into the deserts, along with MOD UDDFS and LLWS.
Blowing dust will locally reduce VIS to 5 miles in the deserts.
Winds will be lighter Tue but local gusts 25-30 kt will occur Tue
afternoon/evening. Otherwise, clear skies with unrestricted VIS
will continue through Tue evening.
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&&

.MARINE...
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No hazardous marine conditions are expected through Saturday.
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&&

.BEACHES...
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A series of southwest swells of 2-3 ft at 16-18 seconds from 200-220
degrees will produce elevated surf of mostly 3-5 ft with highest
sets on exposed SW facing beaches, as well as a high risk of rip
currents at all beaches. The Beach Hazards Statement will expire
this evening as most of the surf will be below 6 ft. Swell and
surf will slowly lower Wednesday and Thursday.
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&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement until 11 PM PDT this evening for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

$$

PUBLIC...SS
AVIATION/MARINE/BEACHES...Maxwell