FXUS66 KMTR 200539
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
939 PM PST Mon Jan 19 2026
...New AVIATION, MARINE...
.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...
(06Z TAFS)
Issued at 932 PM PST Mon Jan 19 2026
LIFR/IFR vis and cigs are expected for the North Bay terminals as
Tule Fog fills in in the vicinity of KAPC and valley fog develops
near KSTS. Expect VFR conditions for remaining terminals to the
south, including Bay Area terminals.
Vicinity of SFO...VFR is expected to prevail through the forecast
period with relatively weak offshore winds prevailing tonight and
through the majority of the forecast period Tuesday.
SFO Bridge Approach...Similar SFO.
Monterey Bay Terminals...VFR is expected to prevail with weak but
persistent offshore flow through the forecast period.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 932 PM PST Mon Jan 19 2026
Light north/northeasterly breezes will increase later in the week
becoming moderate, especially across our northern outer waters.
The weak upper level offshore system expected to move southeast
through our outer waters this week will result in moderate
northwest swell early Wednesday and then again Friday.
&&
.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: Tue Jan 20 02:30:03 PST 2026
From the National Weather Service
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