Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 031614
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
914 AM PDT Mon Aug 3 2020

.SYNOPSIS...
A trough of low pressure deepening over the California coast
during the middle of the week will spread cooling inland through
Thursday. The marine layer will deepen, with night and morning
coastal low clouds and fog spreading farther into the valleys
during the middle of the week. For Friday through next weekend,
the trough of low pressure will weaken with high temperatures
warming to around seasonal averages for next weekend.

&&

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

The marine layer was marginally deeper this morning than it has
been the last 2 mornings but didn`t spread any farther inland. As
a result, we saw significantly fewer locations with dense fog. Sfc
pressure gradients are trending towards weaker onshore and
portions of the coastal areas have already cleared to near the
beaches.

Through Thursday...
High pressure will weaken over southern California and shift to
the southeast as a trough of low pressure deepens along the
California coast for the middle of the week. Desert areas may be a
degree or two hotter today than yesterday as 850 mb temperatures
increase slightly and we lose the low-level moisture surge from
the Gulf of California. This will be followed by general cooling
for Tuesday through Thursday. West of the mountains, a cooling
trend will continue into Thursday. Thursday high temperatures
will be generally around 5 degrees below seasonal averages,
except 5 to 10 degrees below average in some valley and mountain
areas. The lower deserts will be around the seasonal average. As
the trough asserts its influence over the region, we`ll be
effectively cut off from any access to sub-tropical moisture.

The marine layer has deepened to around 1500 feet with widespread
low clouds over the coastal waters extending into coastal areas
and some of the western valleys in San Diego County. The marine
layer will continue to deepen for the the middle of the week,
reaching 2000 to 2500 feet with night and morning coastal low
clouds and fog spreading farther into the inland valleys.

For late in the week into next weekend, the trough of low
pressure will weaken and the high to the southeast will begin to
expand westward into extreme southeastern California. There will
be a warming trend with high temperatures returning to around
average during the weekend.

&&

.AVIATION...
031530Z...Coast/Valleys...Stratus is eroding quickly this morning
and expect VFR conditions at the coastal terminals from 17Z onward.
Low clouds with bases 500-1000 ft MSL and tops to 1500 ft MSL will
reach the coastal terminals again 02-04Z and spread around 15 mi
inland overnight. Areas of vis to 3-5 SM, locally 1 SM or less on
higher coastal terrain from this evening through 15Z Tuesday.

Elsewhere, mostly clear with unrestricted vis through Tue AM. Areas
of smoke near KBUO due to an ongoing wildfire.

Mountains/Deserts...Smoke from an ongoing wildfire will make it into
portions of the San Bernardino mountains and the Coachella Valley.
West winds with sfc gusts 20-30 kt along the mountain crests/desert
slopes and below the passes from 22Z Mon-09Z Tue. Otherwise clear
with unrestricted vis through Tuesday morning.

&&

.MARINE...
No hazardous marine weather is expected through Friday.

&&

.FIRE WEATHER...
Lowest daytime humidity in the deserts and the lower desert
slopes of the mountains will fall to 5 to 10 percent today, then
recover slightly to around 10 percent for Wednesday through
Friday. Sea breeze winds of 15 to 30 mph will continue each
afternoon and evening for the mountains into the deserts. This
combination of wind and low humidity will bring a few hours of
near critical fire weather conditions during the late afternoon
each day from the lower desert slopes of the mountains into the
deserts. The diurnal onshore winds will be strongest Wednesday
and Thursday afternoons and evenings.

&&

.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/FIRE WEATHER...PG
AVIATION/MARINE...Moreland


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