Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 260629
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1029 PM PST Wed Nov 25 2020

.SYNOPSIS...Northerly offshore winds will develop overnight into
Thanksgiving morning in wake of an earlier frontal passage. The
offshore winds will allow temperatures to warm into the mid 60s
most areas Thanksgiving afternoon. High pressure builds Friday
through the weekend with sunny and mild days followed by clear and
cool nights.

&&

.DISCUSSION...as of 09:07 PM PST Wednesday...Cooler and drier
conditions continue to settled into the region this evening in
wake of the frontal passage earlier today. That said, some
locations such as Santa Rosa are experiencing slightly warmer
temperatures compared to 24 hours ago where offshore winds are
mixing down to the valley floors. Winds in the region`s higher
elevations have seen a gradual up-tick out of the north to
northeast through the evening with gusts of 25 to 35 mph being
reported. Short-range guidance indicates these winds will increase
in elevations generally above 1,000 feet through the night and
remain breezy and gusty through Thanksgiving Day. As mentioned in
the previous forecast discussion below, we could see some peak
gusts in excess of 50 mph in the highest peaks of the North Bay.
Thankfully, earlier rainfall this month should help limit fire
weather concerns through late week, yet offshore winds combined
with drying conditions will be closely monitored.

Temperatures region-wide will fall into mid/upper 30s for most
interior locations tonight while 40s are likely elsewhere. This will
make for a chilly start to Thanksgiving with even colder nights
anticipated by Friday morning and into the upcoming weekend as winds
diminish region-wide. This said, the ongoing forecast remains on
track for tonight with no updates anticipated. For additional
details, please see the forecast discussion below.

&&

.PREV DISCUSSION...as of 01:57 PM PST Wednesday...After a somewhat
cloudy and foggy start to the day skies cleared this afternoon
with ample sunshine across the Bay Area. Despite the sunny skies
temperatures are actually running cooler this afternoon. The
cooler weather is thanks to a dry cold front that pushed through
the region earlier today.

The region will see a change behind the front besides just
temperatures. The larger scale synoptic pattern shows a decent
upper trough/low digging through the Great Basin. At the surface
high pressure (>1030mb) builds over the region setting up offshore
flow. Northwesterly flow will begin to shift to more northeasterly
flow later today and more so tonight. The peak of the offshore
still looks to occur late tonight through Thanksgiving evening.
Winds will be strongest over the hills of the North and East Bay.
Some occasional gusts will surface to lower elevations, but the
peak winds will be over the hills. In house local WRF model shows
peak wind of 50-55 mph over Mt St Helena. Needless to say this
would be of greater concern if it were not for our recent rains in
the North Bay, but they will help tamper down fire concerns.
We`ll still be watch it closely though. Winds not strong enough
for enough for a wind advisory however.

The offshore flow will help to dry out the airmass and allow for
pleasant afternoon temperatures heading into the weekend. The dry
airmass will promote radiational cooling at night too, especially
locations that see weaker winds.

12Z runs have now backed off on any precip potential next
Monday/Tuesday for the North Bay. There is an outside chance for a
sprinkle in the North Bay, but dry to the south. Beyond that it`s
not looking good for precip chances. Longer range guidance shows a
low pressure way off the coast the first week of December, but dry
for the Bay Area. CPC long range shows below normal for the
region.

Total side note, but what a difference a year makes on many
fronts(no pun intended). This time last year, Nov-26-28,2019, a
bomb cyclone dropped down the coast bringing wind, rain, and lower
elevation snow to the Bay Area. Much quieter weather this year.

&&

.AVIATION...As of 10:29 PM PST Wednesday...For the 06z TAFs.
Offshore winds and dry air resulting in VFR for the period. Low
level wind shear tonight over the Bay Area with gusty north to
northeast winds aloft. A gradual easing of winds aloft Thanksgiving
Day and surface to lower level diurnal mixing should then minimize
low level wind shear, though with a continued stable air mass and
continuing gusty northeast winds aloft it may redevelop Thanksgiving
night.

Vicinity of KSFO...VFR, west wind 10 to 15 knots overnight. Gusty
northwest winds resuming Thanksgiving Day, mainly in the afternoon
and evening.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR, west to northwest winds 5 to 10 knots
becoming light southeast late evening, locally to around 10 knots
in the Salinas Valley late tonight and Thanksgiving morning. Winds
shifting to northwest near 10 knots Thanksgiving afternoon and light
southeast Thanksgiving evening.

&&

.BEACHES...A long period northwest swell arrives today with
wave heights increasing throughout the day, reaching a maximum of
18 to 24 feet overnight into Thanksgiving morning, with largest
breaking waves at northwest facing beaches. These large breaking
waves, along with brisk northwest winds will enhance coastal
runup. At some shallow northwest facing beaches, runup will
envelop most of or all of the beach. Winds turn offshore Thursday
which will allow large breakers to persist through at least
midday. In addition, enhanced coastal erosion of the summer beach
profiles will continue in earnest with this large swell.
Anomalously cool water temperatures and turbulent, unpredictable
seas will lead to hazardous conditions along the coast. It is
recommended that individuals stay off rocks and coastal jetties if
visiting the coastline and remain vigilant of their surroundings
until a safe distance from the coast.

&&

.MARINE...as of 9:07 PM PST Wednesday...Gusty northwest winds
continuing across the coastal waters tonight, with slight
weakening Thanksgiving Day. Gusty winds will generate steep fresh
swell hazardous for small craft vessels. A large long period
northwest swell train will continue tonight then diminish on
Thanksgiving Day. Another moderate northwest swell arrives late
Friday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...High Surf Advisory...CAZ006-505-509-530
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...SF Bay from 3 AM

&&

$$

PUBLIC FORECAST: RGass/MM
AVIATION/MARINE: Canepa

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