Technical NOAA Weather Discussion

FXUS66 KMTR 291710
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
910 AM PST Mon Dec 29 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 852 AM 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 852 AM PST Mon Dec 29 2025

Temperatures are gradually warming with mostly sunny skies 
anticpated throughout the day. Therefore, the Cold Weather 
Advisory will be allowed to expire at 9 AM PST. We will have to 
monitor for a Cold Weather Advisory again tonight, yet 
temperatures are currently anticipated to be a bit warmer than 
this morning. Otherwise, no changes to the ongoing forecast. 

RGass

&&

.SHORT TERM...
Issued at 126 AM PST Mon Dec 29 2025
(Today and tonight)

Quiet weather continues today as an upper level low slides from 
the Reno/Tahoe area across central California and into the 
Pacific. This can clearly be seen on the water vapor satellite 
channel this morning, while high pressure noses into northwest 
California. Offshore flow dominates the current weather pattern, 
keeping conditions dry and even warm and windy in the terrain, 
especially in the North Bay. In the lower elevations, or where 
temperatures struggled to recover in the mountains yesterday, 
temperatures will be chillier. The Cold Weather Advisory remains 
in effect for the valleys and interior locations, the exception 
being the interior North Bay mountains. The coldest conditions 
happened yesterday morning near or just after sunrise and we 
expect that to happen again today. 

Once we get past the chilly kickstart to Monday, temperatures 
warm into the 50s and low 60s across the Bay Area and into the mid
50s to mid 60s for the Central Coast. 

&&

.LONG TERM...
Issued at 126 AM PST Mon Dec 29 2025
(Tuesday through Sunday)

Cluster analysis in addition to the EPS and GEFS shows upper level 
ridging holding through Tuesday, leading to another quiet day. 
Guidance than clearly depicts ridging building over the 
Intermountain West. Over the Pacific, a cutoff trough deepens and 
gradually lifts north, transitioning more to an open wave feature. 
To the west of that, troughing over the Gulf of Alaska deepens and 
gradually advances westward. Wet weather looks to begin Wednesday, 
with periodic bouts of rain holding through the weekend. Both 
systems look to tap into tropical moisture, with IVTs projected to 
be around 250 kg/(ms). Given last week's storm systems, nuisance 
flooding for poor drainage and urban areas will be possible, as well 
rises on flashy creeks/streams. Given the nice weather over the next 
two days, now is a good time to check storm drains and gutters to 
make sure they're not clogged. The WPC has highlighted Santa Lucia 
Range and Sierra de Salinas in a Marginal Risk for excessive 
rainfall and flash flooding for Wednesday. They also placed the Bay 
Area and the Central Coast in a Marginal Risk for excessive rainfall 
and flash flooding for Friday. Given the already saturated soils and 
the trend in ensemble guidance and QPF cluster analysis, this 
appears reasonable. In addition to rain, confidence is increasing 
for gusty southerly winds for at least the Wednesday round of rain. 
Ensembles have upped the winds as we've gotten closer in time and 
the deterministic models continue to paint a 50kt+ jet at the 950mb 
level. If trends continue, a Wind Advisory may be needed. 

&&

.AVIATION...
(18Z TAFS)
Issued at 910 AM PST Mon Dec 29 2025

High confidence in VFR through the TAF period with the exception of 
STS which can expect radiation fog again tomorrow morning. Winds 
will generally follow a pattern of drainage flow overnight and 
northeasterly winds during the day. Tule fog is not expected to 
impact any terminals directly, but expect it to creep into the area 
from the Central Valley through the Delta and Altamont Pass.

Vicinity of SFO...High confidence in VFR through the TAF period. 
Winds are currently more southeasterly than any guidance/models 
suggest, but they should back through the TAF period to become 
easterly this afternoon and then northeasterly tonight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...High confidence in VFR through the TAF 
period. Drainage winds will continue through the morning with 
northeasterly winds expected this afternoon.

&&

.MARINE...
(Today through Saturday)
Issued at 852 AM PST Mon Dec 29 2025

Moderate 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 945 AM PST Sun Dec 28 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.

PZ...None.
&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Sarment
MARINE...Sarment

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Prepared by Boulder-Creek.com Weather at: Mon Dec 29 10:30:02 PST 2025
From the National Weather Service