Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 211640
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PDT Mon Sep 21 2020

.SYNOPSIS...
Fair and mild weather will continue this coming week. It will be a
little cooler than normal through Tuesday, with greater coverage of
coastal clouds during the nights and mornings. High pressure will
bring warmer weather and less cloudiness Wednesday and Thursday.
Another weak trough will bring cooler weather and more coastal
clouds Friday and Saturday. Next week strong high pressure returns
portending dry and much warmer weather, and locally gusty east
winds will occur below passes and canyons Sunday.

&&

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

Update...

Stratus was a little bit slow to clear this morning, but most areas
should be sunny by around 1030 AM. The marine inversion was almost
10 deg C, fairly strong for September. No changes were made to the
forecast, and a full update to the AFD will be issued early this
afternoon, including more analysis on the possible offshore/easterly
wind event for next Sunday.

From previous discussion...

Today looks like a day we finally get close to normal with
temperatures. The marine layer cloud deck is pretty solid this
morning, extending into far western valleys, but not inland
valleys. Onshore pressure gradients have increased a little,
promising fair weather and seasonal temps and a typical sea
breeze. This week will feature waves or troughs of low pressure
going by to the north, followed by high pressure ridges. We`re in
the trough phase right now, helping to rebuild our marine layer
and bring down the temps today through Tuesday. Some brisk winds
in some mountain/desert passes and corridors can be expected
during afternoons and eves today through Tuesday. Low clouds might
sneak a little farther into the valleys tonight, but most of the
IE should remain clear. Haze and smoke associated with the fires
in the mountains will continue to drift northeast from those
sources. For most folks the skies will continue reasonably blue.
On Wednesday the trough departs and a quickly amplifying ridge
builds. That should squash the marine layer, diminish coastal
clouds, and bring warmer weather Wednesday and Thursday. On
Thursday the next northern trough begins to sag southward into the
West, peaking out Friday. Guidance shows that to spin up a robust
coastal eddy, reversing the trend on the marine layer clouds to
redevelop and spread inland for Friday and Saturday. Temps will go
down again those days. Over the weekend here comes another high
pressure ridge. This one amplifies greatly along the West Coast
for a solid-looking warming trend next week. Some offshore flow is
also possible, which would boost temperatures and lower humidity,
raising the fire potential. It looks like seasonal weather as we
begin autumn on Tuesday (fall equinox arrives at 630 AM PDT), but
the month could end up on a hot summery note next week, albeit
with a fall offshore flavor.

&&

.AVIATION...
211600Z...Coast/Valleys...OVC 1000-1500 FT MSL extending 15-20 miles
inland with VIS of 1-4 miles in clouds and fog. Clouds diminishing
16z-18z across most TAF sites, though some beaches could see BKN
cigs with bases of 1200-1400 ft MSL this afternoon. Stratus to
redevelop across coastal areas after 01z Tue and spread 15-20 miles
inland after 03z, with bases of 600-1000 FT MSL.


Mountains/Deserts...Clear with unrestricted vis (VFR) through
Tuesday night. Surface gusts to develop after 21z with west to
southwest wind gusts to 25-35 kts. This may lead to moderate
updrafts and downdrafts. Winds to diminish after 02z.

&&

.MARINE...
No hazardous marine conditions through Friday.

&&

.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...Maxwell (Update)/MM (Previous Discussion)
AVIATION/MARINE...APR/ES


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