014
FXUS66 KMTR 131832 AAA
AFDMTR

Area Forecast Discussion...UPDATED
National Weather Service San Francisco CA
1032 AM PST Thu Nov 13 2025

...New UPDATE, AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1201 AM PST Thu Nov 13 2025

 - Moderate to heavy rain and a chance for thunderstorms today.

 - Strong wind gusts up to 60 mph may cause property damage,
   downed tree limbs, and difficult travel conditions.

 - Cool and unsettled weather continues through the weekend.

&&

.UPDATE...
Issued at 954 AM PST Thu Nov 13 2025

The short term forecast remains in good shape with some cosmetic
changes to hazards over the next several hours. The High Wind
Warning was cancelled earlier as the conveyor of stronger 925mb
continues to shift eastward this morning. Wind gusts are
anticipated to remain below 45mph across the North Bay and as a
result, wind headlines have been dropped for this region. South of
the Golden Gate, southwesterly wind gusts of at or above 45 mph
are anticipated and may be encouraged within the heavier
downpours. Still, the wind field will ease from northwest to
southeast and a subsequent abatement of surface wind gusts are
anticipated to shortly follow.

Large scale ascent still remains in place and we`ll see shower
activity persist. There does remain some instability that may
support a very isolated thunderstorm threat, however, lapse rates
will likely remain near moist adiabatic and as a result, upward
vertical motion needed to support mixed-phase hydrometeors and
thus lightning production in this main band of rain showers. That
said, satellite imagery does reveal some deeper convective
elements along the trailing cold front and this afternoon will
present the next best opportunity for thunderstorm development,
especially across the southern half of the Bay area and into the
Central Coast. The KMUX VWP did sample an environment
characterized by deep layer shear of 0-6km, so we`ll need to keep
monitor of any deeper convective elements as they`ll have the
ability to realize some of this shear. Organized convective modes,
capable of bursts of stronger winds in addition to transient low-
topped supercellular structures cannot be completely discounted.

&&

.SHORT TERM...
Issued at 1201 AM PST Thu Nov 13 2025
(Today and tonight)

A deep upper level trough and strong surface cold front are
approaching the coast and will bring substantial rain and wind
through the first half of the day. The system is currently
stacked back, meaning the surface low is east of the upper level
low. This configuration implies both divergence aloft and a
strong temperature gradient. The divergence aloft is causing the
surface pressure to drop very quickly. In fact, the low is in the
middle of explosive cyclogenesis (aka a Bomb Cyclone). This was
defined originally by Tor Bergeron in the 1950s as a drop of 24
mb over 24 hours and refined by Sanders and Gyakum in 1980 to
adjust this standard for different latitudes. Using the
adjustment for 40N, the requirement drops to about 18 mb over 24
hours. The Ocean Prediction Center analyzed this low as 1002 mb at
18Z, and most guidance is hovering around 980 mb by 12Z this
morning. That would be a drop of 22 mb over 18 hours, easily
meeting the criteria for a bomb cyclone.

As the surface low deepens and the front gets closer over the
next 12 hours, the pressure gradient will cause the winds to
increase to a strong to southerly breeze that will pump a ribbon
of humid (1.5" PW) air to the Bay Area and Central Coast. The
strongest winds will be along the coast and in the higher
elevations where gusts will routinely reach 60 mph between 3 AM
and 8 AM. So far the strongest gust recorded has been 63 mph gust
at Cobb Ridge located at 3,225 ft in the Mayacamas of northern
Sonoma County. Winds will very gradually decrease through the
afternoon and evening.

We have already seen a few showers and thunderstorms, but the main
show is still a few hours away. The total accumulation so far has
been a few hundredths south of the Golden Gate, with up to 1/2"
in the coastal North Bay Mountains. The main rain band is just
now moving into KMUX radar coverage and will bring steady rain to
the Bay Area commute this morning. The IVT is expected to spike
around 750-1000 kg/m/s and remain above 250 for around 36 hours.
According to the CW3E AR Scale, this qualifies as a strong
atmospheric river. Although the sharp spike may be inflating that
definition, the heavy rain will not last more than a few hours and
we are not expecting widespread river flooding. Be advised,
however, that there will be some roadway flooding as the heavier
rain moves through. Even without standing water, the combination
of the morning rush hour, wet roads, reduced visibility and strong
winds will make for dangerous conditions on the roads this
morning.

The thunderstorm threat is increasing. While the models did not
predict much activity before midnight, mother nature had other
plans. Several lightning strikes were observed across the Central
Coast and East Bay around 8-10 PM. These storms have moved into
the Central Valley and continue to produce some lightning. Mainly
in deference to these earlier storms, we have increased the
chance of thunderstorms embedded in the main rain band to around
20-30%. If more thunderstorms form they will most likely be non-
severe with heavy rain and lightning strikes as the primary
hazard. That being said, the hodographs are nicely curved with
ample low level shear and, while the environment seems to be CAPE
limited with cool surface temps and still high 500 mb temps, we
can`t rule out a water spout or a brief tornado.

&&

.LONG TERM...
Issued at 1201 AM PST Thu Nov 13 2025
(Friday through Wednesday)

While the main show is today, unsettled weather will continue
through the majority of the forecast period. The low discussed
above will gradually become vertically stacked by Friday while
getting cut-off from the jet stream. This will cause the system
to transition from purely baroclinic to partially barotropic as
it parks somewhere near the Channel Islands through Saturday. All
the while the continued southerly flow will support periods of
lighter rain showers, particularly along the Central Coast. The
system will catch the next bus out of town on Sunday as the jet
stream dips back down and kicks the system quickly to the NE. The
trough axis will slide over the coast on Monday bringing a period
of more moderate and widespread rain, followed by strong northerly
winds and colder temperatures. Tuesday looks dry and cool before
a third trough approaches the coast late Wednesday and may bring
even more rain to the Bay Area and Central Coast. The uncertainty
really balloons past Tuesday tough, so don`t give up all hope for
nicer weather next week.

&&

.AVIATION...
(18Z TAFS)
Issued at 954 AM PST Thu Nov 13 2025

Poor flying conditions continue for a majority of the terminals
today due to rain, winds, and ceilings. Outside of +SHRA, cigs are
anticipated to remain MVFR with periods of VFR. Gusty outflow
winds in excess of 20-30 knots are forecast, though this threat
will gradually ease through the afternoon. There`s a risk for
isolated TSRA, most likely across the Monterey Bay Terminals.
Tonight, the forecast is uncertain, but the general trend is
anticipated to be MVFR to IFR ceilings and potentially visibility.
The greatest potential for visibility below 2-3SM resides across
KSTS and KAPC.

Vicinity of SFO...An impactful day will continue at SFO with
periods of SHRA for at least a few more hours, with VCSH through
at least 00Z. Reductions in visibility, down to 2SM or less, and
brief bursts of stronger winds to 30 knots should be anticipated
with +SHRA. Wind gusts have subsided through the morning and I
anticipate that gusts may fall below 20 knots by 20Z. While the
wind direction will remain southerly, the diminished gusts may
allow for a return to the west plan. Confidence in the exact wind
direction is low to medium. Rain showers may return during the
overnight hours and into Friday morning and we`ll refine that in
future TAFs, but at a minimum, we`re unlikely to see wind gusts
exceed 30-35 knots outside of SHRA. Currently anticipating VFR
in the extended portion of the TAF, but scattered cloud decks
below FL040 are forecast and this may impact approach operations.

SFO Bridge Approach...Clouds below FL040 are probable when West
Plan operations continue.

Monterey Bay Terminals...Intermittent SHRA is anticipated through
the afternoon. The instability/fuel for TSRA is greatest across
these terminals, but low confidence precludes the mention of TS at
this time. Gusty/erratic outflow winds in excess of 25-35 knots
and visibility down to or below 2SM should be anticipated with
any SHRA or TSRA. MVFR stratus is forecast after 00Z, however,
with low to medium confidence and refinements probable to the
TAFs.


&&

.MARINE...
(Today through Tuesday)
Issued at 954 AM PST Thu Nov 13 2025

Widespread hazardous marine conditions continue this morning,
conditions gradually diminishing from north to south later in the
morning and afternoon. Gales force winds, heavy rain and a slight
chance of thunderstorms will accompany a strong cold front as it
moves eastward. Winds will then continue to steadily decrease
tonight. Moderate to rough seas will build to become rough for the
inner waters and very rough for the outer waters today through
Friday. Seas abate to become moderate by Saturday.

&&

.BEACHES...
Issued at 124 AM PST Thu Nov 13 2025

A Beach Hazards Statement is in effect from this afternoon through
Friday evening. Long period westerly swell will result in an increased
risk for sneaker waves and rip currents. Breaking waves of 13 to 18
feet with the highest waves up to 23 feet in favored locations are
expected. Sneaker waves can unexpectedly run significantly farther
up the beach than normal, including over rocks and jetties. Rip
currents are typically more frequent and stronger in the vicinity
of jetties, inlets, and piers.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until noon PST today for CAZ006-509.

     Beach Hazards Statement from 3 PM PST this afternoon through
     Friday evening for CAZ006-505-509-529-530.

     Wind Advisory until 4 PM PST this afternoon for CAZ508-510-
     512>518-528>530.

PZ...Gale Warning until 3 PM PST this afternoon for Mry Bay-Pigeon Pt
     to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos
     to Pt Piedras Blancas 0-10 nm-SF Bay N of Bay Bridge.

     Small Craft Advisory until 3 PM PST this afternoon for Pt Arena
     to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes
     to Pigeon Pt 0-10 nm.

&&

$$

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

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