FXUS66 KMTR 131145
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
345 AM PST Thu Nov 13 2025
...New 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.
&&
.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...
(12Z TAFS)
Issued at 345 AM PST Thu Nov 13 2025
A strong cold front will move eastward across the Bay Area and
north Central Coast through morning and afternoon. Strong southerly
winds leading up to cold frontal passage will result in areas of
low level wind shear (llws) mainly nearest the coast, however a
few smaller areas of llws may extend inland as well. Heavy rain
and a slight chance of thunderstorms will accompany the cold
front. VFR-MVFR except IFR in heavy rain along and ahead of the
cold front today. Post cold frontal winds will gradually subside
as will llws in the wake of the front. Low clouds /MVFR-IFR/, less
to much less wind tonight and Friday morning.
Vicinity of SFO...Strong southeasterly wind 25 to 35 kt through
18z this morning, easing somewhat after 18z today. Moderate to
heavy rain today with MVFR ceiling. By late afternoon the cold
front will have moved east of the terminal, winds continue ease
through evening long after the cold front moved by the terminal.
Generally VFR-MVFR tonight and Friday morning.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Low level wind shear (llws) KMRY TAF for
up to 60 knots of south-southeast wind just above the terminal for
the morning hours. As the cold front presses in from the west
during the morning, llws may extend beyond KMRY Airport. Otherwise
well mixed winds are likely surface to aloft e.g. in the Salinas
Valley. Once the downsloping (drying) southeasterly offshore winds
yield to strong frontal convergence, upward vertical motion,
cooler post frontal air bumping into plenty of latent heat release
from a heavy water vapor plume from the subtropics, heavier rain
will develop resulting in IFR conditions. Cold frontal passage
will be west to east, timing approx late morning if not early to
mid afternoon. Rain diminishes to showers after the front moves
through, with lingering showers and diminishing winds much later
today. MVFR with light southeast winds tonight and Friday morning.
&&
.MARINE...
(Today through Tuesday)
Issued at 313 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 to storm 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...High Wind Warning until 10 AM PST this morning for CAZ006-502-
505-509.
Beach Hazards Statement from 3 PM PST 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 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.
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
MARINE...Canepa
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Prepared by Boulder-Creek.com Weather at: Thu Nov 13 06:30:03 PST 2025
From the National Weather Service
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