High Surf in California, January 3, 2021

Area Forecast Discussion
National Weather Service San Francisco Bay Area
220 PM PST Sun Jan 3 2021

.SYNOPSIS...Mostly dry this afternoon and evening with partly
cloudy skies. A storm system moves in late tonight bringing
widespread light to moderate rain and gusty winds to the region
into Monday. Dry weather returns by Tuesday, but an active
weather pattern will continue, with rain chances on Wednesday and
again Friday.

&&

.DISCUSSION...as of 01:05 PM PST Sunday...Satellite shows high
clouds streaming over NorCal and Central CA this afternoon.
Meanwhile, we still have some lingering low stratus clouds across
portions of our CWA including North Bay and the Bay Area. Most of
the visibilities are much better than this morning, but there are
a few spots reporting below 1 mile.

The next storm arrives tonight and models haven't shown any
drastic changes in the forecast. Light, warm advection rain is
still expected near or after 10 pm with the cold front rain moving
inland between 4-10 am on Monday hitting the North Bay first then
moving southward by late morning/early afternoon. As the cold
front moves inland on Monday, this is when we'll see the higher
rain rates. Hi-res models continue to indicate that rain rates
should remain below burn scar thresholds for debris flows. We'll
largely see rain rates around 0.3"/hour or less across our region
during the cold frontal passage, but the NAM shows some very
localized spots seeing brief periods of around 0.5"/hour in the
North Bay. SPC also indicates a slight chance of thunderstorms
which we have for portions of North Bay and adjacent coastal
waters. As always, we'll be monitoring 24/7 in case there are any
threats to the burn scars, but this concern remains very limited.
As for updated rain totals there has been another slight downward
trend...generally by about a tenth of an inch, but that didn't
make much change in the overall forecast rain total ranges. We
continue to see 0.5"-1.5" for the North Bay and Santa Cruz
mountains, 0.5"-1" for the Santa Lucia mountains, 0.5" or less for
valley locations with the lowest amounts being in San Benito and
Monterey counties of less than 0.25". Keep in mind that southerly
winds will be gusty starting early Monday morning through Monday
afternoon with wind gusts 25-35 mph and some local gusts up to 45
mph (mainly in North Bay). Rain will dissipate Monday evening as
we move into a dry and seasonable Tuesday.

On Wednesday, Mother Nature is bringing another batch of rain
chances along a quickly-moving system. Over the last few model
updates, there has been some reduction of chances and rainfall
amounts, making this system much more mild than the Monday storm.
Models and the National Blend are in good agreement that chances
look to start early Wednesday morning and become widespread in the
late morning before breaking apart in the afternoon. The GFS
seems to offer a few light lingering chances into the evening, but
the additional rainfall doesn't look to add up to much. Rainfall
amounts in general from this system look modest with the North Bay
seeing areas adding up to a few tenths, while other portions of
the CWA look to only see a few hundredths.

The current pattern shows another brief pause in rain for much of
Thursday, but another boundary looks to move into the region that
night and could last well into Friday morning. Again the rainfall
amounts look mild, but the GFS offers a deepening trough that could
allow for longer lasting rain chances and the risk of stronger and
gustier winds. For now, GFS's outlook for Friday doesn't seem to be
the most likely scenario, as other models and ensembles do not offer
similar trough developments. After this system, the longer term
models begin to favor a ridging pattern over the weekend giving yet
another break from the rain.

&&

.AVIATION...As of 9:46 AM PST Sunday...For the 18z TAFs. VLIFR-
IFR conditions persist this morning as lingering low level
moisture from recent rainfall allows low clouds and fog to remain
in place. Satellite imagery shows some signs of dissipation for a
few areas with cigs lifting at KSTS and KMRY. Low clouds and/or
fog expected to continue over the next couple of hours before cigs
begin to lift. Even so, low cloud layers are forecast to continue
into the afternoon with some sites remaining MVFR at best
throughout the day. For areas that do clear, clouds will return
this evening and tonight before cigs and vis lower ahead of the
next system. Rain will develop form north to south tonight and
tomorrow with the frontal passage. Periods of fog in typically
favored spots overnight will still be possible when it is not
raining. MVFR/IFR/LIFR conditions prevailing overnight and
through the rest of the taf period.

Generally light winds today and this evening before gusty
southerly winds develop ahead of the frontal passage starting
early tomorrow morning. Recent guidance indicates gusts of 20 to
25 kt, locally higher, towards the end of the taf period.

Vicinity of KSFO...Satellite and webcams show fog lingering over
the south SF Bay and the terminal this morning. Poor visibilities
and low cigs expected to persist for much of the rest of this
morning before conditions begin to improve. However, some low
cloud decks (~1500-3000 ft) are expected to persist throughout the
period. Should conditions improve, cigs and vis will lower again
this evening and overnight ahead of the next front. Shower chances
increase overnight with gusty south to southwest winds developing
tomorrow morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Satellite shows improving conditions at
KMRY with low clouds still hanging over part of the Monterey
Peninsula as well as over the Monterey Bay. Low clouds remain down
the Salinas Valley as well with little sign of improvement at the
moment. LIFR/IFR conditions through the morning remain possible
before some improvement during mid day. Cigs and vis will lower
again this evening and overnight ahead of Monday's cold front.
Patchy fog will be possible again overnight before showers arrive
with rain chances increasing late tonight/early tomorrow morning.
SE winds to pick up down the Salinas Valley tomorrow morning as
well.

&&

.BEACHES...As of 9:30 AM PST Sunday...The initial High Surf
Advisory was allowed to expire this morning as wave heights and
periods subside. However, strong storms in the Pacific continue to
generate large long period northwest swell for the Bay Area and
Central Coast with the next swell set to arrive this evening. The
primary hazard this evening and overnight will be infrequent yet
dangerous sneaker waves and strong rip currents as the initial
forerunners come in at periods of 20 to 22 seconds. Swell heights
will build Monday morning with breaking waves 18 to 24 feet,
locally higher, expected through late Monday afternoon. Waves will
continue to build overnight Monday peaking through Tuesday with
breaking waves of 25 to nearly 30 feet, locally higher at favored
breakpoints. Therefore, a High Surf Advisory will be in effect
from this evening until Tuesday night for an increased risk of
dangerous sneaker waves and large shore break. Additionally, sea
surface temperatures remain cold in the low to mid 50s. Cold water
drownings occur each year with these events but are avoidable by
remaining a safe distance from the coastline. Periods of subsiding
and building northwest swell will continue throughout much of the
week. Continued vigilance is advised.

&&

.MARINE...as of 09:26 AM PST Sunday...Large northwest swell will
continue to create hazardous seas conditions, particularly for
smaller vessels, through the forecast period. Gusty southerly
winds will develop ahead of a cold front that will arrive along
with rain tonight and tomorrow. Winds will gradually turn
southwest tomorrow behind the front before northwest winds return
tomorrow night. Another cold front will move through mid week
bringing more rain and gusty winds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Mry Bay
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

PUBLIC FORECAST: Bingaman/Murdock
AVIATION: AS
MARINE: AS

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