Technical NOAA Weather Discussion

FXUS66 KMTR 072019
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1219 PM PST Sun Dec 7 2025

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 1218 PM PST Sun Dec 7 2025

 - Benign conditions through the next seven days with no
   precipitation expected and a gradual warming trend through the
   later part of the week

 - Impacts from Tule Fog continue in the North Bay and interior
   East Bay valleys, with potential for expansion across the rest
   of the Bay Area overnight

 - Next chance for rain lies slightly beyond the 7-day outlook

&&

.SHORT TERM...
Issued at 1218 PM PST Sun Dec 7 2025
(This evening through Monday)

Today is looking to be very similar to yesterday, right down to the 
satellite imagery showing outgrowth from the Tule Fog across the Bay 
Area, slowly dissipating south of the Golden Gate and west of the 
Berkeley-San Leandro Hills and the eastern Santa Clara Mountains, 
and lingering across the North Bay and interior East Bay valleys. 
Indeed, if you compared the current satellite image and the one from 
yesterday, you could only them apart by the lack of coastal stratus 
today. As a point of curiosity, while there are no radiosonde 
observations over the Central Valley, aircraft soundings from the 
region suggest that the saturated lower atmosphere -- the "Tule fog" 
layer, if you will -- extends 1500-2000 feet above the ground. The 
Central Coast remains mainly clear. 

The remarkably similar evolution of the stratus from yesterday 
through today has lowered confidence in the clearing of stratus from 
the Santa Rosa Plain and the rest of the North Bay valleys. I've 
tamped down the high temperatures today even further in those 
regions, into the upper 40s to the lower 50s, and even then the 
expected highs are still a little warmer than the observed highs 
yesterday. Across the rest of the region, temperatures range from 
the middle 50s to lower 60s across the Bayshore, the Bay Area 
Pacific Coast and the Santa Clara Valley, while the sun-blessed 
Central Coast sees highs in the lower to middle 60s in the Monterey 
Bay region and the Hollister area, and the upper 60s to lower 70s 
inland.

Tomorrow, the ridge over the West Coast will strengthen and continue 
a general warming trend across the region. For the Central Coast, 
the temperature forecast should be similar to today's. The 
uncertainty increases across the Bay Area and especially in the 
North and East Bays, where the impacts of the building ridge on the 
Tule Fog remain uncertain. In general, a building ridge will tend to 
compress the inversion layer, and limit the extent that the Tule Fog 
can extend across the region. (We see this happen during our marine 
layer season as well, when building ridges compress the marine layer 
and prevent it from coming inland.) If the inversion layer does 
compress enough, the Tule Fog could find itself hitting a proverbial 
wall before it reaches the Bay Area. On the flip side, for those 
areas still impacted by the Tule Fog, ceilings and visibilities will 
tend to drop. This makes the temperature forecasts highly uncertain. 
For now, tamped down the temperatures slightly so that the North and 
East Bay valleys see highs in the middle 50s to lower 60s, while the 
rest of the Bay Area valleys see highs in the lower to middle 
60s, but this might be quite optimistic indeed.

&&

.LONG TERM...
Issued at 1218 PM PST Sun Dec 7 2025
(Monday night through next Saturday)

Ridiculously resilient ridging will dominate the weather pattern 
through the rest of the week with the ridge crawling through the 
Western United States, such that over the next 6 days the ridge axis 
moves from just off the coast of the Pacific Northwest to the Oregon-
Idaho border area. Over the Central Coast the impacts are most 
certain with a gradual warming trend in the forecast. The warmest 
days are expected Wednesday through Saturday with highs reaching the 
upper 60s to the middle 70s across the inland valleys. The Bay Area 
in general and the North and East Bay valleys in particular remain 
tied to the evolution of the Tule Fog. Impacts are expected to 
persist into the early part of the work week before diminishing with 
the continuing ridging across the region.

The pattern change for the middle of the month is beginning to come 
into the very end of the 7 day outlook. The early indications are 
pointing more towards a zonal flow pattern for the Western United 
States and any rain storms that develop generally being deflected 
into the Pacific Northwest. Beyond the 7-day outlook, the ensemble 
model clusters suggest that a return to a wetter pattern is possible 
around 9-10 days out, and the CPC's 8-14 day outlook shows a slight 
lean towards rainfall totals above seasonal averages for the third 
week of December. I have heard that before this month...

&&

.AVIATION...
(18Z TAFS)
Issued at 955 AM PST Sun Dec 7 2025

Tough forecast given the Tule fog and associated stratus have not 
been handled well by the models. In fact, most of them for today are 
fairly optimistic, which seems unlikely for much of our service Bay 
Area terminals. The marine layer looks to be 1000-1500ft, with the 
Valley being socked in as of this discussion. Expect cloudy 
conditions to prevail for most sites, with CIGS varying from LIFR to 
IFR. The exception might be KOAK, KSFO, and KSJC where onshore flow 
might be able to mix things out. Where skies are clear, KHAF, 
elevations above 1500ft, and the majority of the Central Coast, VFR 
conditions will prevail. 

Vicinity of SFO...Low to medium confidence in the forecast here 
as most models have indicated some clearing by now and what we 
have seen so far is a slight lift in CIGs. Satellite imagery 
shows some clearing over the San Francisco Bay, but outside of 
that there doesn't appear to be much movement. The most 
pessimistic of forecasts looks to be the MOS guidance from the EC,
which has loosely been incorporated in the TAF for clearing 
around 21Z. After that, opted to keep the previous forecaster's 
TAFs in shape if the onshore flow pans out. Should it not, and we 
stay socked in. The question if that happens will be how long do 
we stay with IFR cigs? Low to medium confidence on this forecast. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Light and variable offshore winds become 
onshore by this afternoon, before circling back to offshore or light 
variable tonight. No VIS or CIG concerns, thus VFR prevail. &&

.MARINE...
(Today through Friday)
Issued at 900 AM PST Sun Dec 7 2025

Moderate to fresh north to northwest winds hold for much of the
waters today with strong gusts focused on the southern waters.
Moderate seas with wave heights 6 to 8 feet across the outer
waters today, subsiding to around 4 to 6 feet for Monday. Winds
increase on Tuesday, with strong to near gale force gusts possible
for much of the waters. A new, long period northwesterly swell is
anticipated by Wednesday of next week.

&&

.MARINE...
(Today through Friday)
Issued at 900 AM PST Sun Dec 7 2025

Moderate to fresh north to northwest winds hold for much of the
waters today with strong gusts focused on the southern waters.
Moderate seas with wave heights 6 to 8 feet across the outer
waters today, subsiding to around 4 to 6 feet for Monday. Winds
increase on Tuesday, with strong to near gale force gusts possible
for much of the waters. A new, long period northwesterly swell is
anticipated by Wednesday of next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 3 PM PST this afternoon for CAZ006-
     506-508-529-530.

PZ...Small Craft Advisory from 3 PM Monday to 3 AM PST Tuesday for 
     Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 
     NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 
     NM.

     Small Craft Advisory until 9 PM PST this evening for Pigeon Pt 
     to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PST Tuesday for Pt Pinos to Pt 
     Piedras Blancas 0-10 nm.

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

&&

$$

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

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Prepared by Boulder-Creek.com Weather at: Sun Dec 7 12:30:03 PST 2025
From the National Weather Service