FXUS66 KMTR 201145

Area Forecast Discussion
National Weather Service San Francisco Bay Area
345 AM PST Thu Jan 20 2022

.SYNOPSIS...Low elevation fog and low clouds this Thursday morning
should give way to mostly sunny sky conditions by the afternoon.
Look for strengthening offshore winds in the higher terrain of the
Bay Area heading into late week with warming daytime temperatures.


.DISCUSSION...as of 03:07 AM PST Thursday...Satellite imagery
early this morning shows less in the way of low cloud cover
compared to 24 hour ago as drier offshore flow has developed
aloft. Meanwhile, areas of dense fog have developed once again in
the North Bay Valleys, across the San Francisco and San Pablo
Bays, along the coastline and locally in portions of the Monterey
Bay. Do expect fog formation to continue through the early morning
hours before slowly eroding by mid/late morning. With this, a
Dense Fog Advisory has been issued through 10 AM PST for the North
Bay Valleys, San Francisco, San Francisco and San Pablo Bays and
along the Bay Shoreline. While some locations just inland from the
bays may remain fog free, major thoroughfares around the area are
likely to see visibility reduced to 1/4 mile or less at times.

Otherwise, high pressure over the eastern Pacific will continue to
build toward the coastline through late week. This will result in a
warming trend with daytime temperatures reaching into the 60s to
lower 70s for most urban areas. Given the dominate high pressure
aloft, dry weather conditions will prevail through the foreseeable
future. Breezy to locally gusty north to northeast winds have
already developed in the region`s higher terrain this morning with
Mt. Diablo reporting wind gusts in excess of 50 mph as of 2 AM PST
Wednesday. Expecting these offshore winds to mainly remain confined
to the higher terrain of the Bay Area through Friday morning.

A mid/upper level low and associated trough will then drop southward
through the Great Basin from Friday into Saturday driving a dry
frontal boundary across the region. This will result in
strengthening 925 mb winds ranging from 35 to 50 kt across much of
the region with some areas likely to exceed 50 kt over the North Bay
and East Bay. Thus, strong and gusty surface winds are likely to
develop first in the higher terrain and then potentially mixing down
to the valleys from late Friday morning into Friday night. Winds
begin to diminish aside from the higher peaks and ridges on Saturday
as the pressure gradient relaxes.

High pressure over the eastern Pacific then continues to dominate
our weather pattern heading into next week. Temperatures look to
remain above seasonal averages with ongoing dry weather conditions.
Forecast ensembles indicate no significant precipitation through the
end of the month. This too is in line with the 6-10 and 8-14 Day
Outlooks from the Climate Prediction Center.


.AVIATION...as of 03:42 AM PST Thursday...For the 12Z TAFs. Dense
fog around the San Francisco Bay, with clearer VFR skies down the
Central Coast. There is a chance for some improved vis around 16Z,
but there is stronger confidence in LIFR conditions through 19Z
for the North Bay, KSFO, and KOAK terminals. The fog is in the
South Bay, but hasn`t reached KSJC yet. There is low confidence
getting there, but a TEMPO group was added as it inches that way.
LLWS is also expected for San Francisco terminals through 16Z. VFR
and breezy northwest winds Thursday afternoon, before winds
diminish Thursday night. Low clouds will try to form Thursday
night, but as an upper level trough moves down the inter mountain
west, winds aloft will increase dramatically. This should provide
enough mixing for clearer skies overnight. However, LLWS has been
added to the terminals after 06Z for these strong winds.
Subsequent forecasts/TAF packages will evaluate the likelihood of
the winds mixing down to the surface.

Vicinity of KSFO...Low clouds and fog sit at the terminal. A Dense
Fog Advisory that includes KSFO will last through 18Z. Winds
aloft are breezy, so LLWS remains in the TAF. Expect winds aloft
to diminish after 16Z. That TAF line item has included a chance
for slightly improved vis; however, there is stronger confidence
that the reduced conditions of LIFR or lower will last through
18Z. VFR and breezy onshore winds Thursday afternoon. Surface
winds subside Thursday night, but northerly winds aloft increase.
LLWS will return and expected to be stronger overnight into Friday
morning. VFR through the end of the TAF.

KSFO Bridge Approach...Low clouds and fog are sitting over the
South Bay providing reduced visibilities on approach.

Monterey Bay...The low clouds overnight have mostly peeled away to
the ocean. A few stray low clouds may linger near coastal
terminals, but otherwise VFR with light winds. Chance for an
increase in southerly drainage winds through the Salinas Valley.
Winds will switch back to the northwest Thursday afternoon. VFR
condition will last through the end of the TAF period.


.MARINE...as of 01:31 AM PST Thursday...Areas of dense fog are
being observed around the San Francisco Bay Thursday morning. Use
caution if on the waters this morning. Fog is not projected to
lift until after 10 AM local time. Winds will remain out of the
northwest and breezy to locally gusty across  the coastal waters
with strongest winds in the northern outermost  waters. Winds
diminish on Thursday, then increase again late  week. Moderate
period west-northwest swell continues into the weekend. Next
northwest swell not expected to arrive until mid- next week.


     .Tday...Dense Fog Advisory...CAZ006-506-508
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             Marine Fog Advisory...SF Bay until 10 AM




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NWS MTR Office Area Forecast Discussion