National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KMTR 280606
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1102 PM PDT Sun Oct 27 2019

.SYNOPSIS...Strong offshore winds are forecast to continue through
tonight and into early Monday, particularly in the hills of the
North Bay. Winds will diminish in all areas by late Monday
morning. Cool nighttime temperatures are expected through much of
the week, especially in the valleys where patchy frost is
possible starting late Monday night. Another round of strong,
gusty, and dry offshore winds are forecast from midday Tuesday
through Wednesday morning across the same areas that are currently
experiencing strong winds. Winds for this next offshore event are
not expected to be as strong, or last as long, as the current
event, but they will still likely generate critical fire weather
conditions when combined with very low humidity.

&&

.DISCUSSION...As of 8:50 PM PDT Sunday...Offshore winds remain
strong and gusty this evening, especially in the hills where gusts
of between 55 and 65 mph continue at the higher elevations in the
North Bay. Winds at lower elevations have been gradually subsiding
since sunset and will likely continue to trend downward
overnight.  Winds in the hills will continue strong and gusty
through the night and will finally diminish on Monday morning. A
High Wind Warning remains in effect for the North Bay Mountains
through 11 am Monday. Wind Advisories remain in effect for much of
the rest of the northern and central SF Bay Area as well as the
Santa Cruz Mountains, through 11 am Monday. The Wind Advisories
for valley locations may be cancelled later this evening if winds
continue to trend downward at lower elevations.

After this current wind event ends tomorrow, two weather concerns
will dominate going forward. The first is another offshore wind
event expected to occur from midday Tuesday through Wednesday
morning. North to northeast winds with this next event are not
expected to be as strong as the current event, or last as long.
However, winds will still likely be strong enough to create
critical fire weather conditions in most, if not all, of the same
areas as this current Red Flag event. See Fire Weather Discussion
below for details. The upcoming offshore event may also require
issuance of Wind Advisories, mainly in the hills of the North and
East Bay.

The second upcoming weather concern regards cool overnight
temperatures. While the airmass over our area is relatively mild
for this time of year, the very low moisture content in the air
will allow for strong overnight cooling once winds subside,
especially in the valleys. Some interior valley locations may see
patchy frost starting late Monday night/early Tuesday, and
continuing through much of the week. We may even see some
overnight lows in the upper 20s later in the week, especially in
the interior valleys of Monterey and San Benito Counties. Frost
Advisories and or Freeze Warnings may be needed for the colder
interior valleys.

Other than another round of strong/dry offshore winds and cold
overnight temperatures in the valleys, our weather for the week
ahead will feature sunny days with mild daytime temperatures
mostly in the lower to mid 70s. Longer range models maintain a
high amplitude upper ridge near the West Coast through at least
the next 10 days, and so rain is nowhere in sight.

&&

.AVIATION...as of 11:02 PM PDT Sunday...VFR forecast except MVFR-
IFR in wildfire smoke in the North Bay, elsewhere smoke aloft will
reduce slant range visibilities to moderate or poor. Surface winds
at the Bay Area terminals will gradually decouple from gusty winds
aloft while to the south winds are overall generally lighter.

Dry air (low dew point temps) and less surface wind combining
tonight will further cooling vicinity KSTS where it could dip to
near freezing yet dry air in place should preclude freezing fog
developing by morning.

Vicinity of KSFO...VFR. N-NE wind settling back to around 10 knots
late tonight. Low level wind shear until 17z Monday morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Wind becoming E-SE 5 to 10 knots
tonight except up to 15 knots late tonight into Monday morning in
the Salinas Valley. Winds becoming light and shifting over to W-NW
by mid to late Monday afternoon.

&&

.FIRE WEATHER...As of 8:45 PM PDT Sunday...No change to current
Red Flag Warnings and they will remain in place through 11 am
Monday. Critical fire weather conditions continue to impact the
region with gusts still reaching as high as 55 to 65 mph across
the peaks of the North Bay as of 8 pm Sunday evening. Winds were
also quite gusty at lower elevations, in the 30-50 mph range,
earlier today. Winds in the valleys have been gradually subsiding
since sunset and are expected to continue to decrease overnight.
However, northeast winds will remain strong and gusty in the hills
through the night, and also locally along the Marin and San Mateo
County Coasts. Winds will decrease significantly in all areas by
late Monday morning. Little or no humidity recovery is expected
tonight, especially in the hills. Very low minimum daytime
humidity, as low as the single digits, will continue through
Monday.

Confidence continues to increase with regard to another offshore
wind event expected from midday Tuesday into Wednesday morning
(the third event over a 7 day period). Latest thinking is this
event will be more like the first event around the middle of last
week, and impact most of the same areas that are currently
experiencing Red Flag conditions. While this next event may not
be a strong as the current event, or last as long, it will almost
certainly result in critical fire weather conditions yet again.
Will let current round of Red Flag Warnings expire before issuing
any new Fire Weather Watch or Red Flag Warning for event number
three.

&&

.MARINE...as of 10:47 PM PDT Sunday...Winds will subside over the
coastal waters overnight, but small craft advisories will continue
due to locally hazardous conditions. Winds will be locally stronger
in the West Delta and along the immediate coast near gaps and passes.
A longer period northwest swell will arrive late tonight into Monday
morning.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Red Flag Warning...CAZ505>507-509>512
             Wind Advisory...CAZ006-505-506-508>512
             High Wind Warning...CAZ507
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: Canepa
MARINE: Canepa
FIRE WEATHER: Dykema/MM

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea