FXUS66 KMTR 300525
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
925 PM PST Mon Dec 29 2025

...New AVIATION, MARINE, BEACHES...

.KEY MESSAGES...
Updated at 226 PM PST Mon Dec 29 2025

 - Cold overnight conditions for interior and valley locations 
   again tonight. 

 - Rain returns Wednesday and lasts through the weekend.

 - Coastal flooding from King Tides is expected Wednesday through
   Sunday.

&&

.UPDATE...
Issued at 906 PM PST Mon Dec 29 2025

Updated the forecast with increased coverage of fog in the North
Bay, which should persist through mid/late morning Tuesday.
Otherwise, expect another cold night, especially across our
interior. A Cold Weather Advisory remains in place for 1AM-9AM
Tuesday morning. Extended guidance appears to be increasing the
wind speeds for the second system moving onshore on Friday,
tomorrow may be the best day to take any outdoor decorations that
survived the Christmas storms last week.

&&

.SHORT TERM...
Issued at 226 PM PST Mon Dec 29 2025
(This evening through Tuesday)

An upper level high is positioned across the northern part of 
California while a cut-off low pressure is in place off of southern 
California. This has allowed for offshore flow in the higher terrain 
which is expected to continue into Tuesday. As such, cold 
temperatures are expected across interior spots of the Bay Area and 
Central coast where overnight low temperatures are forecast to be as 
low as 33 degrees F, isolated colder spots are likely in the wind 
sheltered valleys. Thus, a Cold Weather Advisory has been issued for 
most locations away from the immediate coastline, bay shoreline, 
and the Santa Clara Valley.  

Tuesday will feature increasing mid-to-high level clouds from a 
weather system approaching from the south as the aforementioned cut-
off low advects moisture from the south northward. However, dry 
conditions are expected to prevail with temperatures similar to 
those this afternoon. 

&&

.LONG TERM...
Issued at 226 PM PST Mon Dec 29 2025
(Tuesday night through next Sunday)

The mid/upper level low pressure will advect enough moisture 
northward to spread rainfall across the Central Coast by Wednesday, 
but then will gradually spread northward across the Bay Area by 
Wednesday afternoon. Rainfall amounts will be generally light to 
occasionally moderate with the heaviest being across the Santa Lucia 
and Sierra de Salinas ranges where there is a marginal risk for 
excessive rainfall on Wednesday. Given the recent rain over the past 
week or two, this will lead to nuisance flooding for poor drainage 
areas and urban areas, as well as rises on flashy creeks/streams. 
That low pressure is forecast to shift inland over southern 
California with lingering rain likely into Thursday. 

By Friday, an atmospheric river is forecast to move across the North 
Bay and then progress southward bringing additional rainfall to the 
region and a 10-15% chance for thunderstorms. This is when we are 
expecting the heaviest of rainfall, however the boundary does not 
appear likely to stall at any given point. At this point there is a 
marginal risk for excessive rainfall on Friday across the interior 
Bay Area and Central Coast. Rainfall amounts will be more refined 
as we near late week and get closer to the event. Unsettled 
conditions look to prevail into the weekend and potentially into 
early next week as the pattern aloft remains troughy. 

&&

.AVIATION...
(06Z TAFS)
Issued at 925 PM PST Mon Dec 29 2025

12.0 mb WMC-SFO and 0.8 mb SAC-SFO offshore pressure gradients 
support ongoing offshore winds, dry conditions and high confidence
VFR through late evening. Low clouds and tule fog /VLIFR-IFR/ are
redeveloping over the Central Valley and will reach into the Delta
tonight and Tuesday. Patchy valley fog /VLIFR-IFR/ will also develop
due to radiative cooling tonight and Tuesday morning. The 500 mb 
upper level ridge is forecast to move eastward to Nevada late 
tonight and Tuesday which will shift lower, mid and upper level 
winds to a southerly direction, advecting in high clouds starting 
Tuesday.

Vicinity of SFO...VFR. Southeast to east wind 5 to 9 knots tonight
and Tuesday becoming light and variable by early Tuesday evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Winds mainly east to southeast 5 to
12 knots. 

&&

.MARINE...
(Tonight through next Sunday)
Issued at 920 PM PST Mon Dec 29 2025

Northerly winds and moderate seas will prevail through Wednesday.
Fresh to strong southerly breezes return Thursday into Friday
with gale force gusts likely. Seas build to become rough Thursday
into Friday. Rain returns Wednesday and lasts through the weekend.

&&

.BEACHES...
Issued at 925 PM PST Mon Dec 29 2025

Perigean spring tides (king tides) return Wednesday - Sunday. 
This is due to the combination of the full moon on 1/3, lunar 
perigee on 1/1, and perihelion on 1/3. In other words all three 
planetary bodies are lined up and close to each other. In addition
to the high astronomical tide, the incoming low pressure system 
will bring strong onshore winds, generating some storm surge. The 
combination of these factors will bring minor coastal flooding to 
the low-lying areas near shorelines and tidal waterways during 
high tide Wednesday through Sunday. At the San Francisco tidal 
gauge, high tide is expected to be 1.5 ft above normal at 7:51 AM 
Wednesday, 1.7 ft above normal at 8:41 AM Thursday, 1.8 ft above 
normal at 9:34 AM Friday, 1.8 ft above normal at 10:26 AM 
Saturday, and 1.6 ft above normal at 11:18 AM Sunday. These 
predictions include 0.5 feet of storm surge that will enhance the 
astronomical tide and flooding threat. High tide varies up to 90 
minutes earlier or later along the Pacific Coast and through the 
San Francisco Bay, respectively.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 5 AM Wednesday to 2 PM PST Sunday 
     for CAZ006-505-506-508-509-529-530.

     Cold Weather Advisory from 1 AM to 9 AM PST Tuesday for CAZ504-
     506-510-514>518.

     Dense Fog Advisory until 10 AM PST Tuesday for CAZ506.

PZ...None.
&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Canepa
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Mon Dec 29 22:30:02 PST 2025