Strong Wind in California, February 9 to 10, 2020

Area Forecast Discussion
National Weather Service San Francisco Bay Area
447 AM PST Sun Feb 9 2020

.SYNOPSIS...Strong, gusty, and dry north winds will continue overnight,
mainly in the hills of the San Francisco Bay Area. Gusty winds
will then become more widespread on Sunday and persist through
Monday morning, and perhaps through Tuesday morning in the North
Bay Mountains. Dry conditions will prevail, with a warming trend
forecast for Monday and Tuesday. Slight cooling is expected from
the middle of next week through next weekend, but precipitation
remains unlikely.

&&

.DISCUSSION...As of 3:35 AM PST Sunday...One word describes the
biggest weather impact over the next seven days and that word is
wind. A Wind Advisory remains hoisted for North Bay Mts and East
Bay Hills Area early Sunday morning. Additional areas will see a
Wind Advisory kick in later this morning as stronger winds surface
to lower elevations. Why so windy? Synoptically speaking an upper
level trough continues to deepen and swing through the Great
Basin. Upstream from the trough an upper level ridge continues to
strengthen and build across the PacNW. At the surface, high
pressure is building over the PacNW and the Great Basin with lower
pressure toward the Central Coast. The orientation of the inland
surface high pressure and coastal lower pressure is a perfect
setup for offshore/northerly flow. The added support aloft helps
to strengthen the offshore/northerly wind event. If this were Fire
Weather Season lookout, but fortunately it's February and the
fuels moistures are high and the hills are mostly green. So how
windy is it? Observations overnight are rather impressive over the
higher peaks of the North and East Bay with most gusts in the
30-50 mph range. Mt St Helena is once again an overachiever. Peak
gust thus far for Mt St Helena W is 87 mph and Mt St Helena E 66
mph.

No major change to the previous forecast - gusty winds will
persist over the higher peaks the next few hours. Gusty winds
will gradually mix to lower elevations around sunrise and continue
through roughly midday. The stronger lower elevation winds will
be the Coastal North Bay, San Francisco Peninsula, East Bay
Valleys, San Mateo Coast, and Santa Cruz Mountains. A Wind
Advisory will cover these locations starting at 7 AM. Winds may
ease a bit late Sunday, but latest guidance continues to show
another push of strong winds Sunday night into Monday morning. A
few fringe locations for a Wind Advisory will be North Bay Valleys
and San Francisco Bay shoreline. Winds will be gusty there too,
but shy of criteria. As mentioned on the previous discussion, the
00Z NAM/WRF models keep winds strong through Tuesday morning. The
Wind Advisory may need to be extended for the North Bay Mts again
Monday night, but for simplicity's sake will leave the Wind
Advisory as is for now.

The northerly winds definitely brought drier conditions to the
region with little in the way of clouds/fog early this morning.
The gusty winds area also keeping temperatures up in the valleys
with lows mainly in the 40s. The higher peaks are chilly though
with temps in the 30s. For today, despite the cooler airmass the
downsloping winds will help to warm up temperatures into the 60s.
Further warming is expected on Monday/Tuesday as high pressure
builds over the region with a few 70s possible across the
interior.

Winds will finally relax mid week with a weakening offshore
pressure gradient. Temperatures cool slightly mid week as well
with the high pressure shifting westward. After about Thursday
models take a dive with agreement. The operational ECM still wants
to bring a slight chance of rain to the Central Coast late week,
but ensembles and other operational models say otherwise. Will
follow persistence and keep the current forecast dry at this time.
Would like to see better agreement and more ensemble members
showing rain before adding it to the forecast.

&&

.AVIATION...as of 03:49 AM PST Sunday...For 12z TAFs. VFR
conditions to prevail through the period aside from patchy low
clouds around the Monterey Region this morning. Still waiting on
the stronger winds to mix down to the surface in some places, but
expect that to occur over the next couple of hours. Models still
show winds aloft between 35 to 50 kt at 1500 to 2000 ft AGL, so
expect some LLWS issues when surface winds are lighter. N to NE
winds to increase this morning with sustained winds 15 to 20 kt
(locally higher) and gusts 25 to 35 kt. Winds expected to ease
this evening, but gusts to around 20 kt may continue overnight.

Vicinity of KSFO...UPDATE 04:45 AM. VFR. Winds will continue to
increase this morning with sustained NW to N winds between 15 to
around 20 kt and gusts 25 to 35 kt. Given that winds have
increased quickly this morning and guidance is suggesting wind
gusts later over 35 kt, have gone ahead and issued an AWW from
16z to 20z. Winds will begin to ease this evening but gusts to 20
kt may persist overnight. When surface winds are lighter LLWS may
be an issue with winds aloft between 35 to 50 kt.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Patchy low clouds around the area, but
not expecting persistent BKN cigs. VFR conditions through the
period with increasing winds into the afternoon. NW to NE winds 10
to 15 kt with gusts 20 to 25 kt before winds ease tonight. Models
show winds aloft increasing late this afternoon/early evening to
between 35 to 40 kt. This may create LLWS concerns.

&&

.MARINE...as of 02:50 AM PST Sunday...Gusty gale force northwest
winds will continue into the morning across the coastal waters.
Breezy northerly winds will then persist into this afternoon
before diminishing tonight. These winds will produce steep short
period waves and choppy waters hazardous to smaller vessels. A
moderate and longer period northwest swell will prevail through
the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Wind Advisory...CAZ006-505-509-510-512
             Wind Advisory...CAZ507-511
             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
             GLW...Pt Arena to Pigeon Pt 10-60 nm until 9 AM
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 AM
             SCA...Pt Arena to Pt Reyes 0-10 nm until 9 AM
             SCA...Mry Bay
             SCA...SF Bay until 7 AM
             GLW...SF Bay from 7 AM until 3 PM

&&

PUBLIC FORECAST: MM
AVIATION: AS
MARINE: AS

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