FXUS66 KMTR 301144
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
444 AM PDT Fri Oct 30 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1200 AM PDT Fri Oct 30 2026

 - Moderate coastal flooding at high tide for Bayshore and Pacific
   Coast locations through the weekend

 - Seasonal to slightly below seasonal temperatures through the
   extended forecast

 - Potential for rain Saturday and again next week

&&

.SHORT TERM...
Issued at 1200 AM PDT Fri Oct 30 2026
(Today and tonight)

Satellite imagery is showing a pretty robust stream of high clouds 
into the Bay Area and Central Coast, stemming from the remnants of a 
low from the Central Pacific merging into a wider trough pattern 
across the West Coast. Earlier tonight, some of the embedded 
moisture gave us some rather cool cloud tops on satellite and echoes 
from the KMUX radar and several stations within Monterey and San 
Benito Counties have reported measurable rainfall (up to a tenth of 
an inch) over the last few hours. Although shower coverage has since 
decreased, chances for showers have been added to the forecast for 
Monterey and San Benito Counties through the rest of the morning.

Otherwise, the weather pattern continues to be dominated by a deep 
ridge that has set up across the West Coast. Morning lows will hover 
in the lower to middle 40s in the North Bay valleys, which have 
remained rather clear overnight, and the upper 40s to the middle 50s 
across the rest of the Bay Area and Central Coast. Highs today range 
from the middle to upper 60s in the inland valleys and the SF 
Bayshore, the lower 70s along the warmest parts of the southern 
Salinas Valley, and the upper 50s to lower 60s close to the Pacific 
coast.

A combination of high astronomical tides and surge from thermal 
expansion and low pressure effects brings the risk of minor coastal 
flooding along the Bayshore at the San Pablo, San Francisco, and 
Monterey Bays, and the Pacific coast, at high tide today. At the San 
Francisco tidal gauge, high tide is expected to be 1.9 ft above 
normal (7.7 ft MLLW) at 2:39 PM today, including around 1.5 ft of 
surge residual.

&&

.LONG TERM...
Issued at 1200 AM PDT Fri Oct 30 2026
(Saturday through Thursday)

The trough will start to progress eastwards on Saturday, as the 
trough axis digs into California and an upper level ridge behind it 
starts to push it onshore and into the Great Basin. As it does, it 
pulls in a couple of jet streaks eastwards. One of them will be a 
meridional (north to south) jet streak that will set up to the west 
of the trough, paralleling the coast of Oregon and northern 
California. Quick meteorology lesson -- within a jet streak, the 
balance of all the forces in the atmosphere means that there are two 
regions where cyclogenesis and unsettled weather are favored. Those 
two regions are on the right side of the entrance to the jet streak 
(looking along the direction of wind flow) and the left side of the 
exit of the jet streak. It just so happens that the left exit region 
of the jet streak off Oregon and northern California will help 
provide an impulse to a bit of upper level vorticity, which grows 
into a bigger blob of vorticity, that pushes the trough ever more 
southwards until it develops into its own low pressure system off of 
southern California and the northern part of Baja California. That 
is the storm system that will come into southern California and 
bring some of the attendant moisture into our region. Meanwhile, 
weaker low pressure systems might develop across northern California 
as the jet streak approaches the coast. Rain totals look to be 
around a tenth to a quarter of an inch within the far interior of 
Monterey and San Benito Counties, around a few hundredths of an inch 
in the rest of the Central Coast and orographically favored regions 
of the coastal Bay Area, to a few sprinkles in the interior Bay Area. 
The current forecast has rain coming into the interior Central Coast 
Saturday morning before spreading northwards into the Bay Area later 
on Saturday. Light rain and drizzle may start during trick-or-treat 
hours in the SF Bay Area, but the best chances for rain lie overnight.
A low chance for thunderstorms (less than 10% probability) is 
also present with this system. The conditions might be marginal, 
but with a cold airmass coming with the upper level low, there 
might just be enough moisture, instability, and lift to get some 
convective cells in the higher elevations. K-Index values up to 
25-27 degrees C would support isolated to widely scattered 
thunderstorms. As a final note, high temperatures on Saturday will
dip into the middle 60s for the inland valleys, the lower 60s 
close to the Bays, and the upper 50s to near 60 for the Pacific 
coast.

The rain will clear out Sunday and Monday as the upper level ridge 
comes across the West Coast, and highs in the inland valleys will 
rise to the middle to upper 60s. Beyond that the forecast remains 
uncertain. The current forecast shows some rain chances returning as 
early as Tuesday as another trough or cut-off low comes into the 
region, but the timing of that parent low remains uncertain and 
ensemble model cluster analysis shows a potential delay of the 
incoming rain until Wednesday. Rain chances linger through the end 
of the seven-day outlook, but confidence in any particular scenario 
remains low heading into the latter part of next week.

Coastal flooding concerns continue across Bayshore locations within 
the San Pablo, San Francisco, and Monterey Bays through Sunday and 
the Pacific coastal regions through Saturday. At the San Francisco 
tidal gauge, high tide is expected to be 1.5 ft above normal (7.3 ft 
MLLW) at 3:44 PM Saturday, and 1.0 feet above normal (6.8 ft MLLW) 
at 3:59 PM Sunday, including around 1.5 ft of surge residual.

&&

.AVIATION...
(12Z TAFS)
Issued at 437 AM PDT Fri Oct 30 2026

VFR conditions are expected to prevail through a majority of the
forecast period, with a slight chance of MVFR ceilings developing
early Saturday morning for sites closest to the coast. 

Vicinity of SFO...VFR. There is a slight chance of MVFR ceilings
developing early Saturday morning, however there is much
uncertainty to if/what extent the marine layer will reorganize
before another fetch of offshore flow Sunday and Monday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR today and tonight with a slight
chance of MVFR ceilings late in the forecast period. Similar as
above, there is much uncertainty in how well the marine layer can
or will reorganize before another fetch of offshore flow Sunday
and Monday.

&&

.MARINE...
(Today through Wednesday)
Issued at 437 AM PDT Fri Oct 30 2026

Northerly breezes will continue to be gentle to fresh with
moderate seas today and into the weekend. A long period
southwesterly swell this weekend will combine with a long period
west-northwest swell by the beginning of next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 6 PM PDT Sunday for CAZ006-506-508-
     529-530.

     Coastal Flood Advisory until 6 PM PDT Saturday for CAZ505-509.

PZ...None.
&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...JM
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Fri Oct 30 08:30:03 PDT 2026