Technical NOAA Weather Discussion

FXUS66 KMTR 280535
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
935 PM PST Sat Dec 27 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 1209 PM PST Sat Dec 27 2025

 - Calm, clear and cool conditions through mid week.

 - King tides and rain chances arrive with the new year.

&&

.UPDATE...
Issued at 848 PM PST Sat Dec 27 2025

Another calm night is ahead, but this time the cooler airmass 
continues to build. This will lead to some of the coldest 
temperatures of the week, with Cold Weather Advisories going into 
effect for portions of Monterey Co and all of San Benito Co later 
tonight and into the morning. The cooler pattern looks to continue 
over the next few days, leading to concerns for more Cold Weather 
Advisories.

&&

.SHORT TERM...
Issued at 1209 PM PST Sat Dec 27 2025
(This evening through Sunday)

We just flipped the radar back to clear air mode as the stormy 
weather is now firmly in the rear view mirror. High pressure has
returned to the Eastern Pacific, bringing back our familiar 
northerly winds. This regime is bringing cooler and drier air. 
While the increased sunshine is keeping temperatures mild in the 
afternoon, enhanced radiational cooling with the long clear night 
will bring the coldest temperatures we've seen in a couple weeks 
Sunday morning. The interior Central Coast is under a Cold Weather
Advisory, and the North Bay Valleys should get close to reaching 
the 36 degree threshold. The two limiting factors are high clouds 
streaming in from the North , and the current dew points in the 
mid 40s. The temperature can't drop below the dew point, so in 
order to get into the mid 30s, there will have to be robust fog 
formation to remove water vapor from the air and lower the dew 
point. Fog formation slows cooling in 2 ways. First the actual 
change of state from gas to liquid releases latent heat. Second 
the low level clouds block outgoing longwave radiation, limiting 
surface cooling. Don't be surprised to see Tule fog return as this
set up seems perfect for it. 

While the trough responsible for the Christmas storm is 
moving to the East, it will leave a small cut-off low over 
southern California. As this happens the EPAC ridge will build 
over the top, creating an inside slider pattern and supporting 
offshore winds early in the week. The SFO-WMC gradient is
currently +2 mb, but should bottom out around -7 to -10 mb Sunday
afternoon as the new pattern develops. This will reinforce the 
clear and dry conditions, while bringing the day time temperatures
up a few degrees.

&&

.LONG TERM...
Issued at 1209 PM PST Sat Dec 27 2025
(Sunday night through next Friday)

These offshore winds will continue Monday as the PWAT plummets
below 0.3", or the bottom 10th percentile for this time of year.
The same trend of cold foggy mornings with clear afternoons in the
mid 50s will continue into Wednesday. The same cut-off low that
caused the offshore winds will spend the first half of the week 
continuing to meander SW, well into the subtropical NE Pacific. 
By Wednesday it should get picked up by the next long wave trough,
helping to amplify the pattern. This will bring uncommon southerly
winds and tropical moisture to the area. It's almost monsoon like
if it wasn't the end of December. The PW will climb well above 1"
before the associated cold front barrels through on the 1st or
2nd. We'll likely get a good rain ahead of the front with showers
in the post frontal cold air. There's obviously some timing 
details to work out, but the general pattern has a remarkable 
amount of confidence considering the complexity. The ensemble 
clusters all show some version of this unfolding.

&&

.AVIATION...
(06Z TAFS)
Issued at 935 PM PST Sat Dec 27 2025

The larger scale WMC-SFO pressure gradient will strengthen tonight
through Sunday night resulting in offshore winds reaching the Bay
Area. A mainly clear sky will help with radiative cooling and 
patchy fog redevelopment tonight and Sunday morning. Will also 
have to monitor tule fog redevelopment in the Central Valley and 
the potential for a return of tule fog into the Bay Area, though 
at the time being the HRRR model shows greater tule fog development
Sunday night into Monday. The offshore winds develop before then,
tule fog development and transport of tule fog could start as soon
as early Sunday morning due to recent rains and moistened boundary
layer. KSTS and KAPC have fog in the TAFs due to nocturnal radiative
cooling, otherwise it's a moderate to high confidence VFR forecast
for the remainder of the terminals.

Vicinity of SFO...VFR. Mainly northeast winds 5-7 knots tonight 
through Sunday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Winds east-southeast 5-10 knots and
continuing into early-mid Sunday afternoon, then becoming light 
and variable to light onshore in the late afternoon. Light east to
southeast winds redevelop Sunday night.

&&

.MARINE...
(Tonight through next Friday)
Issued at 848 PM PST Sat Dec 27 2025

Hazardous marine conditions will slowly decrease tonight due to
northerly winds diminishing and rough seas abating. By tomorrow
afternoon, moderate northerly breezes and moderate seas will
prevail. High pressure and dry weather return for the weekend and
early next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Cold Weather Advisory from 2 AM to 9 AM PST Sunday for 
     CAZ516>518-528.

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

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Canepa
MARINE...Canepa

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea


  
Prepared by Boulder-Creek.com Weather at: Sat Dec 27 22:30:02 PST 2025
From the National Weather Service