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

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FXUS66 KMTR 171212
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
412 AM PST Sun Dec 17 2017

.SYNOPSIS...Gusty northerly winds and dry conditions will continue
this morning, especially over the North and East Bay hills. Winds
will then diminish, but with dry conditions and above average
daytime temperatures continuing through the first part of the
week. A Pacific weather system is projected to move rapidly
southeastward through Northern California Tuesday night and
Wednesday, with rain chances spreading southward into the greater
San Francisco Bay Region. High pressure then looks to rapidly
rebuild along the coast with dry weather and seasonal temperatures
for the latter part of the week and next weekend.

&&

.DISCUSSION...as of 03:30 AM PST Sunday...Aside from some thin
high cloudiness drifting through, mostly clear skies prevail
across our district. Winds continue to be locally strong and
gusty in the North and East Bay hills and am therefore continuing
the Wind Advisory for these zones into the morning. Elsewhere
winds have generally diminished and the Wind Advisories have been
cancelled. Will note that at a few locations the winds did
surface. Napa Airport, in particular, stood out as a low elevation
site with an interval of strong winds during the overnight hours,
recording a peak gust of 43 mph at 1:25 AM PST. The Red Flag
Warning remains in effect across all higher elevation portions of
our district until 10 AM PST.

The ridge of high pressure now building into the West Coast will
persist through the first part of the week, but then looks to
begin weakening and shifting inland as a strong upper level system
moves rapidly southeastward through the Pacific Northwest.
Although latest model output continues to show the primary
associated precip band moving inland to our north, more recent
solutions have trended westward and now do bring its tail end
through our district in a late Tuesday night to Wednesday time
frame. Have therefore begun ramping up associated PoPs, and noted
just received 06Z runs of the NAM and GFS are a bit wetter still.
That said, rainfall totals are likely to be on the small side,
given the limited moisture supply and rapid speed of movement.

As we then head into the latter part of the week, high pressure at
the surface and aloft again looks to rapidly rebuild along and
into the West Coast, with dry conditions and offshore flow
returning for the latter of the week and into next weekend.

&&

.AVIATION...As of 4:00 AM PST Sunday...Dry northerly flow will
bring VFR conditions through Monday. Stronger winds aloft will
cause low level wind shear this morning. Winds decrease after 18Z.

Vicinity of KSFO...VFR. Northerly winds gusting as high as 40 kt
above 1000 feet will cause low level wind shear through 16-17Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR.

&&

.FIRE WEATHER...as of 3:35 AM PST Sunday...A Red Flag Warning
remains in effect through 10 AM PST Sunday for elevations at or
above 1,000 feet across the entire region. Dry conditions will
persist with early morning maximum humidity values likely confined
to the 20 to 30% range, especially in the higher elevations.
Along with the very dry air mass, breezy to gusty winds will
continue during the morning hours, especially over higher
elevations in the North and East Bay hills. Wind speeds are then
forecast to diminish, however dry conditions will continue into
the first part of the week.

&&

.MARINE...as of 3:02 AM PST Sunday...A broad thermal trough
positioned over California will maintain moderate winds over the
northern outer coastal waters with lighter winds along the coast
through Friday. Steep fresh swell is expected to accompany the
moderate winds across the northern outer waters. The thermal
trough is anticipated to slide west Friday afternoon promoting
generally light southerly winds and improving sea conditions into
the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Wind Advisory...North and East Bay Hills until 10 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 2 PM

&&

$$

PUBLIC FORECAST: Blier
AVIATION: W Pi
MARINE: W Pi
FIRE WEATHER: W Blier

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