High Surf in California, December 31, 2019

Area Forecast Discussion
National Weather Service San Francisco Bay Area
932 AM PST Tue Dec 31 2019

.SYNOPSIS...Dry and mild conditions will prevail through Friday,
as high pressure remains along the West Coast. Daytime
temperatures will be warmer than normal, while nights will be
seasonably cool. Patchy valley fog will be possible during the
night and morning hours. Rain chances return to the North Bay this
weekend, and weekend daytime temperatures will be slightly cooler.
Large surf will bring hazardous conditions to area beaches from
Tuesday afternoon through Wednesday evening.

&&

.DISCUSSION...as of 09:00 AM PST Tuesday...Visible satellite
imagery this morning is showing a band of high clouds spreading
southward over the greater San Francisco Bay Area. Surface
temperatures are generally in the middle 40s to lower 50s with
readings likely to warm into the upper 50s to lower 60s by this
afternoon. Overall, the ongoing forecast remains on track with no
updates needed at this time. For additional and complete forecast
information, please see the forecast discussion below.

&&

.PREV DISCUSSION...As of 3:10 AM PST Tuesday...The longwave pattern
aloft shows the storm system that brought rain a few days ago
spinning off the SoCal Coast. Farther north, a ridge of high
pressure is building across the EPac and nosing its way into OR
and NorCal. Satellite imagery shows a few high clouds spilling
over the ridge of high pressure, but most of the Bay Area is
clear. Breezy to gusty conditions continue over the higher peaks
of the North/East Bay and Santa Cruz Mountains. Gusts of 20-40 mph
have been recorded the last few hours. On the flip side, lower
elevations are seeing much less wind and many valley locations are
reporting light to calm. The combination of mostly clear skies
and light winds will lead to some chilly temperatures with lows in
the 30s and 40s. The lingering low level moisture may also lead
to some patchy valley fog this morning. Otherwise, the ridge of
high pressure will continue through at least Friday. Temperatures
will warm each each day and peak on Friday with highs in the upper
50s to mid 60s - or a few above normal for early January.
Overnight lows will remain chilly, 30s and 40s, coldest interior
valleys. A little extra focus on NYE - temperatures will be
pleasant this evening and mostly in the 50s, but by midnight
they'll be dropping into the 40s. Skies will start out mostly
clear, but mid-high level clouds will gradually increase.

Confidence is gradually increasing for a change in the pattern
next weekend. Medium range models, operational and ensembles, are
showing some consensus in breaking down the ridge with a low
pressure system. A low pressure system is forecast to moving into
the PacNW Friday evening and ultimately drag a cold front into
NorCal. The tail end of the front is forecast to bring a slight
chance for showers into the North Bay Saturday morning. Therefore,
a slight chance of showers will be in the forecast for Saturday.
At this point it appears rain chances stay north of the Golden
Gate.

&&

.AVIATION...as of 9:32 AM PST Tuesday...For 18z tafs. Dry north
to northeast flow should keep VFR conditions today with high level
clouds between 10,000 and 20,000 ft AGL. Generally light winds
today becoming onshore at the coast and Bay Area this afternoon
with offshore winds persisting inland. Expecting winds to remain
at or below 10 kt. Latest models still showing an increase in low
level moisture late tonight and through tomorrow morning. This may
create areas of reduced visibility around the Bay Area. Models
and guidance also show potential for the development of low cigs
around the Bay Area late tomorrow morning that may persist into
the afternoon. Confidence is low at this point on those possible
cigs. Patchy fog will also be possible around the North Bay.

Vicinity of KSFO...VFR. Light east to northeast wind this morning
becoming west to northwest to 10 kt after 21Z. Possible reduced
visibilities tomorrow morning and late tonight due to increased
low level moisture. The development of low cigs will also be
possible tomorrow morning and maybe into the afternoon. Confidence
is low at this time.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR through the period with high clouds
around 20,000 ft AGL. Light southeast winds this morning becoming
light onshore in the afternoon.

&&

.MARINE...as of 09:00 AM PST Tuesday...Low pressure off of the
southern California coast will continue to move southward today
resulting in a slight decrease in northwest winds by tonight. High
pressure building off of the central California coast will move
closer to the coast Wednesday night and Thursday resulting in an
increase in northwest winds. A long-period northwest swell will
arrive this afternoon with a larger swell arriving on Wednesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm until 1 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 1 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

PUBLIC FORECAST: RGass/MM
AVIATION: AS
MARINE: AS

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