High Wind Watch 1, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1013 AM PST Fri Jan 31 2020

.SYNOPSIS...Warmer temperatures expected today with daytime highs
inland reaching well above seasonal averages. Significant cooling
is projected over the weekend. Sunday looks to be particularly
chilly and breezy with even lower elevation highs confined largely
to the 50s. Can't completely rule out the possibility of a few
showers too for the North Bay, as a cold upper level trough moves
through from the northwest. Cool and dry conditions then look to
continue into the first part of next week.

&&

.DISCUSSION...as of 08:38 AM PST Friday...With weak winds around the
Bay Area, fog has developed around Santa Rosa, down the Pacific
coastline, and in the Salinas Valley. Web cams have also showed a
shallow low cloud layer around San Francisco. As the sun shines, it
will help mix out the clouds and the fog will leave later this
morning. Temperatures will warm later today into the 60s.

The next main system being monitored is the cold front coming in
overnight Saturday into Sunday morning. Afternoon temperatures will
drop by about 10 degrees, with overnight lows on Monday morning in
the 40s, with isolated areas of the North and East Bays in the 30s.
Strong winds will be associated with it, particularly along the
coast. Light rain can't be completely rules out for the North Bay,
but chances are small and accumulations would be minimal. Otherwise
the forecast for cooler and drier conditions for next week remains
on track.

&&

.PREV DISCUSSION...as of 2:57 AM PST Friday...High clouds moving over
the state are obscuring the satellite view of low clouds below.
Current surface observations indicate a few areas with low clouds,
and Hollister, Santa Rosa and Napa are reporting dense fog with
1/4 mile visibility or less. Current temperature readings are
mainly in the 40s to lower 50s. As the upper ridge axis moves over
the state, look for slightly warmer high temperatures today with
60s to lower 70s expected, above normal for this time of year.
Saturday should be slightly cooler as an upper level trough
approaches the coast, although most areas should still see highs
in the 60s.

On Sunday, the upper trough will move onshore across Northern
California towards the Great Basin. This will usher in a much
colder airmass, and sharply tighten the N/S surface pressure
gradient for windy conditions developing first over the coastal
waters, then inland, especially near the coast and in the higher
terrain. Gale conditions are expected to develop on Sunday, and
wind advisories may also be needed over portions of the district
Sunday going into Monday. High temps will be markedly cooler,
dropping more than 10 degrees over highs the day before, with
lower to mid 50s forecast. Widespread rainfall is not expected,
although a few showers or sprinkles are possible as this trough
moves through.

Dry and chilly conditions will persist through early in the week
with cold, near-freezing morning low temperatures possible on Monday
and Tuesday. High pressure will rebuild over the coast during the
week with gradually moderating temperatures expected.

&&

.AVIATION...as of 10:05 AM PST Friday...For 18z tafs. High
pressure overhead with generally light offshore winds (locally
breezy in favored valleys) and passing high clouds. A patch of fog
NNE of KSFO was diminishing in the last hour but a wind shift
towards the north has allowed it shift back over the runway and
drastically dropped visibility and cigs. If winds hold N/NNE/NE(as
they are expected to do so through around 20-21Z) could possibly
see this fog bank linger near the KSFO approach through 1930-2030Z
depending on the rate of decay/expansion of the fog bank over the
San Francisco Bay. Low clouds/fog redevelop to an extent tonight
into tomorrow morning. Looking beyond the taf period, a dry
frontal boundary will bring very wind conditions on Sunday.

Vicinity of KSFO...Watching a deck of low clouds/fog expand and
drift over the KSFO runways late this morning, with an expected
clear out time of around 20Z given a persistent N/NE direction to
the winds. Otherwise, winds 10kt or less, with low clouds
redeveloping overnight tonight and high clouds through the
duration.

SFO Bridge Approach...Low clouds at KSFO not present over SMB but
will impact final approach through the rest of the morning.

Monterey Bay Terminals...VFR with high clouds. Breezy up valley
winds in the Salinas valley with light onshore near the coast. Low
clouds/fog redevelop overnight into tomorrow morning.

&&

.MARINE...as of 10:02 AM PST Friday...High pressure will bring
light to locally moderate northwest  winds through the day
Saturday. Northwest winds strengthen  significantly through
Saturday night and into Sunday ahead of a  frontal boundary. Gale
to locally storm force winds are possible  Sunday into early
Monday morning. These strong winds will generate steep waves and
create hazardous seas conditions over the waters. Moderate
northwest swell will continue through much of the  forecast
period. Small craft advisories for seas at or above 10 feet in
effect through 10am this morning.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...NONE.

&&

PUBLIC FORECAST: Sims/DK
AVIATION: DRP
MARINE: DRP

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