035 
FXUS66 KMTR 201110
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
410 AM PDT Mon Oct 20 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1249 AM PDT Mon Oct 20 2025

 - Warm and dry weather through Tuesday.

 - Less than 15% chance of thunderstorms across Central Coast 
   Tuesday night into Wednesday.

 - Beneficial rain returns Friday through Sunday.

&&

.SHORT TERM...
Issued at 1249 AM PDT Mon Oct 20 2025
(Today and tonight)

Another quiet fall day is on tap, with the main forecast highlight 
being another round of offshore winds developing tonight and 
continuing into Monday. Observations already show north to east 
winds over the North Bay region, while areas south have onshore 
flow. Expect offshore winds to continue to materialize overnight and 
linger into Monday. These winds will also usher in drier air to the 
region, which should keep much of the area stays free. The exception 
might be around Monterey Bay, as an otter eddy formed earlier in the 
evening and circulated some log clouds around it.  Stratus may 
continue to do this dance overnight, teasing coastal Monterey County 
and the northern Salinas Valley with low clouds and patchy fog 
through the morning. Once the sun comes out, skies should clear and 
high temperatures will be beautiful, with 70s near the coast and 80s 
inland. 

Monday night into Tuesday, a southerly surge of stratus returns and 
creeps up the coast. Expect the marine layer to be around 500 feet 
bringing cool, cloudy, and foggy conditions for coastal
communities.

&&

.LONG TERM...
Issued at 1249 AM PDT Mon Oct 20 2025
(Tuesday through Sunday)

The extended forecast continues to remain interesting as models and 
ensembles show a cut off low that has been meandering off the coast 
of southern CA moving slightly to the north and then inland. One 
thing we know for certain with this system is that cooler 
temperatures will be ushered into the region, and the marine layer 
should deepen to around 1200 feet or so. Stratus should form along 
the coast and perhaps seep into some interior valleys. Where 
uncertainty lies with this system is the threat for thunderstorms. 
Deterministic guidance and some ensembles show the chance for 
isolated thunderstorm activity starting late Tuesday evening across 
portions of the Central Coast into Wednesday. As daytime heating 
allows, some guidance adds the threat of isolated thunderstorms 
along the higher areas of terrain for the East and South Bay 
counties. A fair amount of convective ingredients are available, mid 
level lapse rates around 7-7.5C/km, a couple hundred J/kg of MUCAPE, 
PWATs near 0.80", and lift from the low. The limiting factor seems 
to be shear at this point. For now, no mention of thunderstorms have 
been added into the forecast. Chances look to be around 14% or less, 
but that could change as we get more into CAM territory. 
Thankfully we have had some decent rain in the past, so fire weather 
concerns are low. 

After a cool Wednesday, we will see an uptick in high temperatures 
as weak ridging noses into the region on Thursday. An area of low 
pressure off the Gulf of Alaska will deepen, allowing for upper 
level troughing and zonal flow to take over. At this time it looks 
like beneficial rain appears to be the most likely solution as 
ensembles continue to trend towards lower amounts Friday - Sunday. 
Right rainfall amounts look like this: North Bay counties may see 
around 0.50-1.25", East Bay counties, Santa Cruz County, and the San 
Francisco Peninsula around 0.15-0.50", Santa Clara 0.10-0.40", and 
finally Monterey and San Benitio counties 0-0.15". These amounts 
will likely change, so stay tuned to the forecast. 

&&

.AVIATION...
(12Z TAFS)
Issued at 410 AM PDT Mon Oct 20 2025

Generally VFR throughout the region, excepting LIFR stratus and fog 
developing in the Monterey Bay and Salinas Valleys, along with 
shallow fog at STS. Confidence for stratus at HAF has decreased as 
the offshore flow on the nearby ridgelines might keep the terminal 
clear. Speaking of offshore flow, while the gradients are too low to 
mention LLWS in the TAFs, stronger winds aloft might make for bumpy 
takeoffs and landings through the morning hours. Stratus should mix 
out by the late morning hours with a gentle onshore breeze at the 
coastal terminals during the afternoon and evening. Otherwise, light 
winds continue through the day. This evening, offshore winds develop 
across the interior with light winds at the coastal region, with 
some stratus in the Monterey Bay region.

Vicinity of SFO... High confidence of VFR through the TAF period. A 
gentle west-northwest breeze in the afternoon and evening, otherwise 
winds remain light.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Models have struggled to capture the LIFR 
stratus and fog that has developed across the region and down the 
Salinas Valley. Currently expecting the stratus to stick around 
through the late morning hours, with breezy onshore winds in the 
afternoon. Stratus returns to the terminals tonight as the winds 
become light, with moderate confidence on timing.

&&

.MARINE...
(Today through Saturday)
Issued at 410 AM PDT Mon Oct 20 2025

Northwest swell combined with fresh to strong northwest breezes
are causing very rough seas. The winds will steadily decrease
from Monday into Tuesday, allowing the seas to gradually subside
before a new long period northwest swell arrives early Tuesday
night and again on Thursday night.

&&

.BEACHES...
Issued at 1249 AM PDT Mon Oct 20 2025

A Beach Hazards Statement is in effect runs through 8PM Monday 
evening as a long- period swell impacts the Pacific coast. Never 
turn your back to the ocean! Swim near a lifeguard if possible! If
caught in a rip current, swim parallel to shore until you escape 
its influence. 

Additional beach hazards lurk in the forecast beyond Monday, when
another long period swell arrives. This may lead to another Beach
Hazards Statement or a High Surf Advisory possible depending on 
how the forecast evolves.

&&

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

PZ...Small Craft Advisory until 9 AM PDT this morning for Pt Arena to 
     Pt Reyes 0-10 nm.

     Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt 
     to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 PM Tuesday to 9 AM PDT Wednesday for 
     Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 3 AM to 9 AM PDT Wednesday for Pigeon 
     Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...DialH
MARINE...DialH

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