Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 312011
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
110 PM PDT Sat Oct 31 2020

.SYNOPSIS...
High pressure aloft will continue warm days and cool nights across
Southern California well into next week. A shallow moist layer will
maintain areas of dense fog near the coast and over the coastal
waters through Sunday, while higher clouds drift overhead. We will
see a noticeable change in the weather by the end of next week as a
trough brings much cooler weather with strong westerly winds over
the mountains and deserts, and even a chance for some light
precipitation west of the mountains.

&&

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

Satellite imagery continued to show patchy low clouds/fog over our
coastal waters at midday. Huntington Beach still had dense fog but
most other areas had improved. The fog was becoming more difficult
to see due to increasing high clouds from the south, but most areas
still had sunny skies. An offshore trend has boosted sfc pressure
gradients enough to fuel gusty NE winds below passes and along the
coastal slopes and below passes. Peak winds of 35-40 MPH have been
recorded, along with very low relative humidity inland.

Some dense fog may still reappear along the Coast overnight, but
given the offshore flow, and increasing high clouds, any dense fog
should remain patchy and not obscure your view of the brilliant
Hunter`s Moon this evening rising in the east. This Halloween
spectacle may help you remember to "Fall Back" this evening as we
head into Standard Time again early Sunday morning. Then, look for
another sunny and warmer day to start the month of November.

The upper low associated with a rex block over the EastPac will
be pulled north over the CA Bight through Sunday as the associated
ridge axis drifts eastward. Several disturbances circulating about
the upper low will pull some elevated moisture and instability over
SoCal through Monday. Look for some high clouds that could drop a
few sprinkles, and the instability could spark some isolated pockets
of downdraft winds over the mountains, but no thunder or significant
rain is expected for now. Patchy dense fog may remain trapped over
the coastal waters and reach some beaches through at least Sunday.

The upper low opens and drifts inland on Tuesday, helping to weaken
the offshore flow. This should result in minor cooling, but daytime
temperatures will continue above average, and very warm again
through midweek as the ridge aloft strengthens.

More noticeable weather changes are in the works for the weekend.
There is a broad model consensus that a disturbance in the westerly
wind belt far to the north will take dive south over the EastPac and
swing inland along the West Coast. Besides bringing strong westerly
winds to our mts/deserts, it will mean much cooler weather, and even
a chance for some light precipitation early next weekend. Details
and timing are yet to be worked out, but for now small POPS are
broadly brushed into the fcst from late Fri night through Saturday.

&&

.AVIATION...
311925Z...A few low clouds with localized fog will persist this
afternoon at the beaches. Low clouds and fog likely to return to
coastal areas vcnty TAF locations after 03Z Sunday. Bases expected
to remain below 400 ft MSL with locally dense fog restricting vis to
1 mile or less at times. Moderate confidence in cig and vis impacts
at TAF sites between 05Z and 14Z Sunday. Expect clearing to the
beaches 15Z to 18Z Sunday.

Otherwise, mostly clear with unrestricted vis through Sunday.

.MARINE...
Patchy low clouds and fog with visibility around 1 nautical mile or
less may form again tonight. Otherwise, no hazardous marine
conditions are expected through Wednesday.

&&

.FIRE WEATHER...
Weak to locally moderate offshore flow inland will continue through
Monday. Lowest daytime humidity of 10 to 15 percent, combined with
locally gusty east to northeast winds of 15 to 25 MPH and isolated
gusts to 35 MPH below the passes, will continue elevated fire
weather conditions in these areas. The afternoons will be quite warm
through the middle of next week, even as the dry air rapidly gives
up that heat each evening. More high clouds will overspread the
region as well, due to instability and moisture with weak low
pressure aloft, but at this time no weather is expected.

The upper low will help to weaken offshore flow further Tuesday and
Wednesday, which should trend us slightly cooler, with a moderation
in RH. Temperatures will remain above average, but wind gusts are
expected to be 25 MPH or less for most areas.

After a very warm Thursday, a pattern change will turn winds
decidedly onshore Friday, with strong westerly winds possible over
the mountains and deserts into next weekend. There is also a small
chance for light showers along and west of the mountains early next
weekend.

&&

.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...10
AVIATION/MARINE...PG


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