Special Marine Warning 7, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
200 PM PDT Mon Oct 4 2021

.SYNOPSIS...
An upper level low pressure system off the northern Baja California
coast will move slowly northeast across the area through Tuesday.
This will bring cooling and periods of scattered showers and
isolated thunderstorms this afternoon into Tuesday. The cooling
trend will continue through Friday with additional chances of
precipitation on Thursday and Friday with gusty southwest winds in
the mountains and deserts. Dry warmer weather will return next
weekend.

&&

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

Scattered light showers and isolated thunderstorms were moving
north over San Diego County and the adjacent coastal waters at early
afternoon. The lower layers of the atmosphere remained dry with mid-
morning AMDAR soundings with low humidity below 750 MB, and dry
conditions continue as there is a lot of virga and only minor
amounts of precipitation reaching the ground. The highest precip
amount so far has been Granite Hills at 0.03". Temperatures were
lower versus Sunday, generally by 3 to 10 deg F.

The upper low will move northeast across far SoCal, and with a lot
of instability aloft tonight, more showers and isolated
thunderstorms will occur. Some rainfall amounts could reach one-half
inch (0.50") through Tuesday, though most locations will receive one-
tenth (0.10") to one-quarter (0.25") of an inch, but amounts will be
quite variable due to the convective nature of the precip. The
precip should exit to the northeast Tuesday afternoon, if not sooner.

A long-wave trough of low pressure will develop over the West Coast
Wed/Thu with the trough axis likely moving through around Fri,
though with some uncertainty in timing. Despite some indications of
a weak atmospheric river possible either in SoCal or far northern
Baja California, ensembles show rather light precip amounts, mostly
less than one-half inch but with great variability (0 to over an
inch) in the ensemble output. Thursday night/Friday is the most
favorable period, but the rain could come as early as Thursday
morning. This trough will bring continued cooling as well, with
daytime temperatures likely 5-15 deg F below normal by Friday. Due
to the increasing height gradients aloft, a round of gusty southwest
winds will likely occur in the mountains and deserts, most likely
Thursday night. Fair weather should return next weekend with a
warming trend.

&&

.AVIATION...
041945Z...VCSH and slight chance of Isold TSRA moving from south to
north through 07Z Tue with cloud bases lowering to 5000-8000 ft MSL.
Increasing chance of ISOLD/SCT SHRA/TSRA, 07-11Z Tue. Isold TSRA
will have lightning and could contain +RA reducing vis 1-5SM along
with erratic winds. After 11Z Tue, VCSH expected through 15Z.

After 15Z Tue... SCT-BKN clouds AOA 10,000 ft MSL.

&&

.BEACHES...
Lightning strikes are possible at the beaches through early Tuesday
morning. Thunder and lightning are most likely overnight tonight.
Please check with your local authorities on potential beach closures
for hazardous water conditions caused by the oil spill.

&&

.MARINE...
A Marine Weather Statement is in effect for possible thunderstorms
that produce lightning and/or gusty erratic winds through early
Tuesday morning. Otherwise, no hazardous marine weather is expected
through Saturday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Tuesday morning for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

PUBLIC...Maxwell
AVIATION/MARINE/BEACHES...CO