616
FXUS66 KMTR 101657
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
857 AM PST Wed Dec 10 2025

...New UPDATE...

.KEY MESSAGES...
Updated at 1224 AM PST Wed Dec 10 2025

 - Hazardous beach conditions through Friday.

 - Tule fog and stratus continue for the North and East Bay.

 - Light rain remains possible next week.

&&

.UPDATE...
Issued at 856 AM PST Wed Dec 10 2025

This morning we are seeing less cloud cover over the Bay Area
with the North Bay, East Bay and South Bay seeing similar
conditions as yesterday. As such, low clouds may clear earlier
than yesterday but there is low to moderated confidence of that
actually occuring. As mentioned in the short term discussion
below, persistence seems to be the best with respect to afternoon
maximum temperatures. We will continue to monitor these conditions
and adjust if necessary. Otherwise, no updates to the ongoing
forecast at this time.

RGass

&&

.SHORT TERM...
Issued at 1224 AM PST Wed Dec 10 2025
(Today and tonight)

Tule fog and stratus continue with very similar coverage to 24
hours ago. In addition to the entire Central Valley, most of the
North Bay and the interior East Bay are impacted by this
persistent radiation fog. This is caused by unmoving high pressure
bringing clear, dry, and calm conditions to the troposphere.
Combined with long December nights, nocturnal radiative cooling
from both the Earth`s surface and cloud tops are enhanced. Since
the cooling is coming from the bottom up, it`s very stable (cold
air sinks). And since the cooling at night is enough to reach
saturation and form or bolster the existing clouds, a positive
feedback loop sets up where the clouds then block incoming
sunlight during the day. All this works to keep the day-time
temperatures cool under the clouds, and the models have been
struggling to capture just how cool. Kentfield stayed between 43
and 46 degrees all day Tuesday. The forecast is challenging
because there is very warm air just above the clouds. The 850
temperature has blown past the 90th percentile is now approaching
the daily max on record. Boulder Creek stayed clear and reached
78 degrees yesterday. This big discrepancy between the thin cold
layer and everything else is really tough to nail down. When the
advanced weather models let us down, we often fall back on the
most rudimentary form of forecasting in existence: persistence. In
other words, what happened yesterday will happen today.
Specifically Tuesday`s high temperatures are making up 66% of the
forecast for Wednesday. With an unchanging pattern, that`s not a
bad guess. If the clouds clear early though, watch out for
temperatures to spike. Areas outside of the clouds (Central Coast,
SF Peninsula) will have cooler mornings and warmer afternoons.
Maybe just a couple degrees warmer than yesterday.

&&

.LONG TERM...
Issued at 1224 AM PST Wed Dec 10 2025
(Thursday through Tuesday)

Temperatures should climb a degree or two each day through Friday
before the ridge axis finally moves through on Saturday. That will
mark the end of this prolonged boring pattern as a more zonal jet
stream moves in. We should finally see some high clouds by Sunday
with a chance for rain starting Monday or Tuesday. While we are
finally losing the ridge, we`re not getting a substantial trough,
so any rain bearing systems should be relatively light. On the
other hand the active zonal flow could bring these weaker systems
in quick succession. CW3E shows both the ECCC and NCEP AR
activity anomaly peaking around +2 AR days per week from
12/15-12/21 before falling back to near the climatological norm
for the following 2 weeks. In other words if we don`t get any
substantial rain next week, there is no strong signal for it to
come during the rest of the month. Perhaps the best chance is
around the 20th, but there`s a lot of uncertainty. The 00Z ECMWF
ensemble members range from 0.0" to 8.4" of total rain at SFO
through the 21st. So the total dispersion is massive, but the
more reasonable interquartile range is 0.4" - 2.0". The GEFS is
drier with a medial closer to 0.5". Temperatures will cool this
weekend, but should remain warmer than normal through next week.
The CPC temperature outlooks are about as confident as we ever
see that it will remain warmer than normal for the next couple
weeks, but that doesn`t necessarily take our famous microclimates
into account.

&&

.AVIATION...
(12Z TAFS)
Issued at 324 AM PST Wed Dec 10 2025

Higher confidence in clearing out of the fog and stratus today for
North Bay terminals. Day-to-day change gradually improving as high
pressure builds aloft. Patchy stratus invof SF Bay providing lower
confidence there, but based on persistence forecast KOAK likely to
remain VFR.

Vicinity of SFO...Patchy stratus around the Bay this morning, but
much less coverage than 24 hours ago. Some stratus invof the
terminal may linger through sunrise. Not enough confidence to
include in TAF attm. Most of the area around the terminal,
including bridge approach, expected to remain mostly stratus-free.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...High confidence in VFR through the TAF
period. Light drainage offshore winds overnight with light onshore
flow during the afternoons.

&&

.MARINE...
(Today through Monday)
Issued at 324 AM PST Wed Dec 10 2025

Northerly fresh breeze continues across the outer waters with
lighter closer to shore. Light offshore flow through the San
Francisco Bay and Delta result in light easterly flow through the
Golden Gate. A new, long period northwesterly swell anticipated to
arrive today, lasting into this weekend.

&&

.BEACHES...
Issued at 1224 AM PST Wed Dec 10 2025

Long period swell will reach the coast Wednesday - Friday. This
energy brings strong rip currents, an increased risk for sneaker
waves, and large breaking waves. The Bodega Bay Buoy is reporting
a WNW swell of 9 feet with a 13 second period. That translates to
breaking waves of 12-16 feet along west facing beaches. This
coincides with nice warm weather, which will likely lure more
people to the beach under a false sense of security. A Beach
Hazard Statement is in effect through Friday evening. Respect the
power of the ocean and never turn your back on it.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Friday evening for CAZ006-505-
     509-529-530.

PZ...Small Craft Advisory until 9 AM PST this morning for Pt Pinos to
     Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 AM PST Thursday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 3 PM PST this afternoon for Pigeon Pt
     to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Behringer
MARINE...MM

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