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300
FXUS66 KSGX 100943
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
243 AM PDT Fri May 10 2024

.SYNOPSIS...
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There is a slight chance of showers over the San Bernardino and
Riverside County mountains this afternoon and evening. Areas of
night and morning low clouds and fog will continue across portions
of the coastal areas and valleys through the week. Gradual
warming inland through Sunday followed by minor cooling Monday and
Tuesday. Inland warming trend will resume on 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...

Marine layer low clouds are struggling to organize over San Diego
County this morning, but have filled in across Orange County with
some patchy development in the Inland Empire. Elsewhere skies are
clear. Clouds will gradually fill in across the valleys by
sunrise, then slowly clear back towards the coast by the early
afternoon.

Water vapor imagery shows an upper level low centered over NV with
a trough axis extending west to the Central CA coast. This wave will
rotate around the base of the low through tonight, pulling the
low further southwest towards So Cal. There is marginal mid- level
moisture with this low and High Level Total Totals around 34-36
for the San Bernardino Mountains northward. This should be
sufficient for at least isolated showers over the higher peaks of
the mountains Riverside and San Bernardino Counties this
afternoon and evening. Elsewhere dry weather will prevail with
highs a few degrees below normal.

The upper low drifts east through the weekend with an upper level
ridge setting up over the Southwest. This will bring steady
warming inland through Sunday with highs likely reaching the
triple digit mark in the low deserts. By Sunday highs will be
around 5-9 degrees above normal inland, but the persistent marine
layer will keep temperatures west of the mountains closer to
normal. The marine layer will become more shallow over the
weekend with less inland extent of cloud cover. The strengthening
marine inversion will make it harder to get clearing at the coast
during the afternoons.

A weak closed low will slowly move across the region Monday and
Tuesday, bringing minor cooling and allowing the marine layer to
deepen once again. Beyond about Tuesday ensemble spread increases
considerably regarding the position of the E Pac upper high and
the placement of any downstream troughing. It`s currently around a
50/50 split on a stronger ridge into the Pac NW and warmer weather
here versus weak troughing across the Pac NW or a western
displacement of the high, resulting in cooler weather for So Cal.
These differences continue through the end of the week. The range
of potential high temperatures is quite massive - around a 20
degree spread for the inland valleys to the deserts, but only
around 5-10 degrees for the coastal areas and western valleys
since the marine layer will stick around either way. Temperature
forecast left with deterministic NBM which closely follows the
50th percentile.
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&&

.AVIATION...
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100930Z...Coast/Valleys...Areas of low clouds with bases 1800-2600
ft MSL and tops to 3500 ft will occur overnight, though some areas
may have only brief/intermittent CIGs. Local VIS 1-4 miles will
occur in BR, mainly in the valleys through 16Z, with local terrain
obscurations in clouds. The valleys will clear 16Z-18Z, with partial
clearing near the coast 18Z-21Z as some locations will have a BKN
CIG 2100-2700 ft MSL lasting through Fri afternoon. Low clouds will
spread farther inland Fri evening.

Mountains/Deserts...SCT/BKN clouds will develop again Fri afternoon
over the mountains with bases around 9000 ft MSL with local TCU
possible. Otherwise, mostly clear skies will prevail through Fri
evening with unrestricted VIS.
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&&

.MARINE...
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...None.
PZ...None.

&&

$$

PUBLIC...SS
AVIATION/MARINE...Adams