Brentwood, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

635
FXUS66 KMTR 241214
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
414 AM PST Tue Dec 24 2024

...New MARINE...

.SYNOPSIS...
Issued at 1130 PM PST Mon Dec 23 2024

Hazardous surf conditions continue today, with the addition of
rain and wind from a passing cold front. Showers are possible
through the afternoon before a much nicer day Wednesday. The break
won`t last long as rain chances return to the forecast Thursday
and persist through the weekend.

&&

.SHORT TERM...
(Tonight through Wednesday)
Issued at 1130 PM PST Mon Dec 23 2024

The main concern continues to be hazardous conditions along the
coast. Large breaking waves will continue to produce deadly
conditions through the day. More information on this threat is in
the "BEACHES" section below.

Prefrontal warm air advection has been very productive over the
last 4 hours. In fact SFO literally feels like Miami at this
moment (both 64 degrees with a 61 dew point). Beyond the novelty
fact, this actually has real forecast implications. The warm humid
air mass will enhance instability as the cold, dense air mass
wedges underneath. This will increase shower activity and
thunderstorm chances as the front pushes through. Otherwise the
front is progressive enough to bring more beneficial type rain,
without widespread flooding concerns. Winds will shift from
southerly to westerly, and will gust as high as 30 mph as the
frontal boundary passes in the early morning. Later Tuesday
morning into the early afternoon, rain chances continue, but will
switch to scattered convective showers in the post-frontal
environment. The instability is high enough to support some strong
showers or thunderstorms, especially if the sun is able to peek
out in the morning. Showers will taper off as the day wears on,
and Tuesday night looks dry. While Santa should stay dry, he may
have to contend with some fog Christmas morning, especially in the
valleys.

&&

.LONG TERM...
(Wednesday night through next Monday)
Issued at 1130 PM PST Mon Dec 23 2024

After the short break Wednesday, rain returns to the forecast
Thursday and continues through the weekend. A series of
disturbances will bring a couple inches of rain the the Bay Area,
with a focus in the North Bay. The Russian River at Guerneville
has a 10% chance of reaching minor flood stage and a 5% chance of
reaching moderate flood stage by Sunday. This disturbed weather
will also bring periods of gusty winds, foggy conditions and
warmer than average temperatures.

&&

.AVIATION...
(12Z TAFS)
Issued at 342 AM PST Tue Dec 24 2024

The cold front has just crossed San Jose and is continuing to
march south at a good pace. A narrow band of heavy rain is
preceeding the front, with weaker scattered showers in the cold
air mass behind the front. The latest high resolution guidance
suggests these showers will gain strength through the morning
before the skies begin to clear in the afternoon. Thunderstorms
are still possible in the late morning or early afternoon, but
the probability is decreasing.

Vicinity of SFO...MVFR conditions will persist for the next
several hours, although the brunt of the impacts have already
passed. Winds have shifted back to WNW and will remain there
through the day. A few stray showers are possible, but overall
the terminal will enjoy improving flight conditions through the
day. With a fresh coat of rain and clearing skies, fog is possible
Wednesday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...These terminals are currently
experiencing frontal passage, but the system is weakening and the
rain intensity is much lower than earlier. Despite this, SNS is
still under persistent LIFR ceilings through the first half of the
morning, with visibility restrictions possible between the
transient rain showers.

&&

.MARINE...
(Today through Sunday)
Issued at 414 AM PST Tue Dec 24 2024

Significant wave heights are very high, but beginning to abate
this morning. Large westerly swell, strong currents, and floating
debris will continue to make conditions hazardous for small craft
today. A passing cold front will bring gusty winds, moderate rain
and possible thunderstorms through the afternoon.

&&

.BEACHES...
Issued at 943 PM PST Mon Dec 23 2024

A High Surf Warning remains in effect through 6 pm Tuesday for
breaking waves of 30-40 ft with up to 60 ft along favored spots. A
Coastal Flood Warning is also in effect through 12 pm Tuesday as
these large waves run up the coast.

The Scripps Point Sur Buoy peaked at 27.9 ft significant wave
height/20 second period at 7 pm, and has since dropped back to 23
ft. Of note, this buoy has only reported larger waves 4 other
times since 2008 (Dec 2023, Jan 2023, Jan 2017, Dec 2015), and
only once with a 20 second period or longer (Dec 2023). While most
buoys are reporting a similar trend, and the peak may have past,
conditions are still incredibly dangerous along the coast. With
the measured 20 second period, 23 ft swell still has the potential
to generate 33-39 ft breakers depending on the bathymetry, with
every 100th wave on average reaching up to 58 feet on a
moderately steep beach (1:33 slope). This is all based on shallow
water wave physics, and where the "largest wave sets up to 60 ft
at favored spots" wording came from in the High Surf Warning. The
very slow abating trend will last through the day Tuesday before
more substantial improvement on Wednesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Warning until noon PST today for CAZ006-505-509-
     529-530.

     High Surf Warning until 6 PM PST this evening for CAZ006-505-509-
     529-530.

PZ...Small Craft Advisory until 3 PM PST this afternoon for SF Bay N
     of Bay Bridge.

     Small Craft Advisory until 9 AM PST Wednesday for Mry Bay.

     Small Craft Advisory until 3 PM PST Wednesday for Pigeon Pt to
     Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to
     Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to
     Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Flynn
MARINE...Flynn

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea