369
FXUS66 KMTR 130942
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
142 AM PST Thu Nov 13 2025

...New AVIATION, BEACHES...

.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.

&&

.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...
(06Z TAFS)
Issued at 142 AM PST Thu Nov 13 2025

Generally VFR conditions with mid- to high-level clouds and high-end
MVFR continue through the next few hours. Southerly winds are
expected to increase tonight, with their delayed arrival increasing
the uncertainty over the current forecast for the peak wind
intensity. Isolated showers are currently observed with the coverage
increasing throughout the early overnight hours followed by the main
frontal rain band combined with the strongest southerly winds and
generally MVFR-IFR conditions progressing from the North Bay after
midnight through the rest of the region through Thursday morning.
Thunderstorms have already impacted the Monterey Bay terminals
tonight. Further thunderstorms can not be ruled out, but confidence
in timing and location of convection remains low. The likeliest
chances for convection (15-25% probability) are in the coastal
regions and the interior Central Coast.

UPDATE: Added low level wind shear (llws) to KMRY TAF for up to
60 knots of south-southeast wind just above the terminal for the
morning hours. 925 mb frontogenesis may help keep surface winds
decoupled from winds aloft vicinity KMRY with generally momentum
mix down of winds aloft to the surface at the other area
terminals; will closely monitor pireps, surface observations, etc.
and amend TAFs if needed. With the approaching cold front, heavy
rain and wind with frontal passage later this morning and
afternoon winds aloft will begin to diminish. concerns as the
front passes through, and although the magnitudes remain too low
to include in the TAFs, bumpy takeoffs and landings are still
anticipated. After the front passes, southerly winds relax and
lingering showers persist through the tail end of the TAF period.

Vicinity of SFO... VFR with mid-level clouds to high-end MVFR and
isolated showers persist through the early overnight hours.
Southeasterly flow will increase through the next few hours, with
gusts of at least 30-35 kt expected overnight through Thursday
morning. The delayed onset of strong winds has decreased confidence
in the wind forecast. The main rain band passes through Thursday
morning and brings generally MVFR conditions. After the front
passes, expect improving conditions, relaxing winds, and lingering
showers through the end of the TAF period.

SFO Bridge Approach... Similar to SFO.

UPDATE: Monterey Bay Terminals...As mentioned, added low level
wind shear to the KMRY TAF for up to 60 knots of south-southeast
wind just above the terminal for the morning hours (through 19z
today), including tempo IFR in heavy rain 19z-23z closer to the
strong cold front arrival. Otherwise VFR conditions with mid-
level clouds continue through early Thursday morning. Southeast
flow will increase through the overnight hours and peak on
Thursday morning and afternoon, as the main frontal rain band
passes through the region. Generally MVFR conditions are expected
as the main front moves through. The main band should be beginning
to exit late Thursday afternoon, with lingering showers and
decreasing winds through this period.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 939 PM PST Wed Nov 12 2025

Widespread hazardous marine conditions continue to deteriorate
across the waters through Thursday morning. Rain showers will
increase in coverage and intensity into Thursday morning with
embedded thunderstorms possible. Widespread gale force gusts are
expected through Thursday morning with storm force gusts expected
for the northern waters. Winds will quickly diminish Thursday
night. Moderate to rough seas tonight will build to become rough
for the inner waters and very rough for the outer waters Thursday
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...High Wind Warning until 10 AM PST this morning for CAZ006-502-
     505-509.

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

     Wind Advisory until 10 AM PST this morning for CAZ503-504-506.

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

PZ...Gale Warning until 9 AM PST this morning 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.

     Storm Warning until 9 AM PST this morning 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...Canepa/DialH
MARINE...DialH

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