FXUS66 KMTR 200406
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
806 PM PST Mon Jan 19 2026

...New UPDATE...

.KEY MESSAGES...
Updated at 1230 PM PST Mon Jan 19 2026

 - Dry weather, cool mornings, and mild afternoons this week

 - Morning fog across the Delta, North Bay Valleys, and interior 
   East Bay Valleys 

&&

.UPDATE...
Issued at 755 PM PST Mon Jan 19 2026

It looks like the Northern Lights are going to be a bust tonight.
The clouds are holding off, but the geomagnetic activity has
plummeted from the G4 level observed this afternoon to less than
G1 at the latest measurement. The issue is the orientation of the
magnetic field generated by the strong coronal mass ejection. 
When it first hit earlier today, the incoming field was oriented 
south, which is opposite of the earth's magnetic field, and 
allows for enhanced energy transfer into our magnetosphere. Europe
was getting a good display thanks to their earlier sunset. In the
early afternoon the orientation of the CME field flipped to 
northerly, in line with the earth's field. This blocks the energy 
transfer and is a big hindrance to the geomagnetic storm and thus
the aurora. While it's still possible for the field to flip back 
southerly, the raw strength is also waning. It's still worth 
taking a peek, but don't hold your breath.

&&

.SHORT TERM...
Issued at 1230 PM PST Mon Jan 19 2026
(This evening through Tuesday)

Very little change in day to day conditions anticipated through mid 
week. A ridge of high pressure remains just off of the Pacific coast 
that will continue to result in temperatures 5-10 degrees above 
average (up to 15 in the higher terrain). Overnight, we are 
expecting patch to areas of fog in the North Bay Valleys while tule 
fog (dense at times) is forecast to advect westward into the 
interior East Bay Valleys and Delta again either late tonight or 
into Tuesday morning. If driving or commuting in these areas; be 
aware of the potential for dense fog and be prepared for sudden 
changes in visibility, remember to slow down, and use your low beam 
headlights. 

Expecting a slight cool down on Tuesday as more widespread high 
clouds stream over the region, but only by a few degrees. Where 
mostly sunny sky conditions prevail, afternoon temperatures will 
warm into the mid 60s to lower 70s across the Central Coast and low 
to mid 60s elsewhere. That said, where fog lingers into late morning 
or early afternoon, expecting temperatures to only reach the upper 
50s.

&&

.LONG TERM...
Issued at 1230 PM PST Mon Jan 19 2026
(Tuesday night through next Sunday)

Dry conditions look to persist through much of the extended 
forecast. An upper level trough will develop over the north central 
Pacific between Tuesday night and Wednesday. A cut-off low will 
develop within that trough and move southward just off of the Bay 
Area/Central Coast, resulting in slightly cooler conditions and 
cloudier skies through late week. Thus, the greatest potential for 
rain will be across southern California and along the Santa Lucia 
Range on Thursday as a deeper plume of moisture advects inland to 
the south. However there is about a 20% probability of seeing 
greater than 0.01" and less than a 10% chance of that area seeing 
0.10" over that area. 

A weak upper level ridge is forecast to develop by this weekend and 
into early next week. As a result, a slight warming trend is 
forecast, but not as warm as what we have been the past week. Longer 
range guidance continues to push back our next potential widespread 
rainfall. It is not until late January or early February that we 
forecast widespread rain to return to the region. 

&&

.AVIATION...
(00Z TAFS)
Issued at 324 PM PST Mon Jan 19 2026

VFR is expected to prevail for all terminals except KSTS where
valley fog is expected to develop late tonight and persist 
through late morning Tuesday. Otherwise, we'll see light winds and
drifting high clouds from south to north.

Vicinity of SFO...VFR is expected to prevail through the forecast
period with low confidence, low chance of MVFR stratus in 
vicinity of KOAK and KSFO overnight into earl Tuesday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR is expected to prevail through the
forecast period with increase in offshore winds Tuesday morning 
through the remainder of the day.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 324 PM PST Mon Jan 19 2026

Light northerly breezes will continue through the middle of the
week and begin to gradually increase by the end of the work week
into next weekend across our northern outer waters. A weak upper
level disturbance will result in a subtle increase in
northwesterly swell to moderate both Wednesday and Friday, quickly
easing again into the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...JM
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Mon Jan 19 20:30:02 PST 2026