Weather Service Report


437 
FXUS66 KMTR 061746
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
946 AM PST Tue Dec 6 2016

.SYNOPSIS...Look for continued cool conditions into Wednesday with
areas of frost possible tomorrow morning. A weather pattern
change will occur during the second half of the week, with periods
of rain likely from late Wednesday potentially through the
weekend.

&&

.DISCUSSION...as of 8:51 AM PST Tuesday...Low clouds and patchy
fog continue to impact portions of the region this morning, mainly
southern/inland areas of the Central Coast and around portions of
the East Bay. Do see improving sky/visibility conditions across
this region though since sunrise. Meanwhile, passing high clouds
will continue to stream across the region today with temperatures
warming into the 50s for most locations. The ongoing forecast for
the short-term remains on track and no updates are needed at this
time. Will focus our attention to the upcoming weather pattern
change that will result in widespread precipitation across the
region for the second half of the week.

&&

.PREV DISCUSSION...As of 3:00 AM PST Tuesday...Look for two chilly
mornings (today and tomorrow) before rain returns to our region
for the second half of the week. Thanks to drier air across our
region plus fewer clouds compared to yesterday temperatures are
running anywhere from 3 to 7 degrees cooler in most spots. A few
North Bay spots are already in the mid 30s and will probably drop
to around 30 by sunrise. Most urban spots around the Bay Area will
be in the 40s with a few upper 30s likely. 

Tonight will be a near repeat of today although many spots will
likely be a few degrees cooler. Based on the latest guidance,
values will drop close to some of our frost/freeze levels. Will
let the day shift make the call after the morning lows for today
come in plus full slate of 12Z guidance. Right now have majority
of metro locations tomorrow morning in the mid 30s to the lower
40s.

Later on Wednesday that synoptic pattern will undergo a major
switch as the dry northwesterly flow is replaced by a much wetter
zonal flow due to an approaching longwave trough. At the same
time a plume of moisture extending well to the west of Hawaii
will move directly toward the coast. This will bring rain into the
North Bay first and slowly to the the bulk of our CWA by Thursday.
Right now appears that the morning commute will be the worst for
the North Bay and then down to the SF Bay Area for the afternoon
drive.

After a brief break in the rain a second shot of moisture will
move back to our CWA late Friday through Saturday as the plume
slowly works down the coast. Similar to the first push, PW values
will remain quite high (potentially over 1.40" at the coast and
over 1.30" inland). Rain will mostly end by Sunday.

QPF forecast into Sunday is close to yesterday morning with
locally 3" possible for coastal ranges. Generally look for 1-2"
in most urban spots.

Models diverge for next week with the latest GFS keeping wet
conditions going through the middle of next week while the ECMWF
shows a break for Monday and Tuesday.

&&

.AVIATION...As of 9:40 AM PST Tuesday...Low clouds are scattering
out quickly this morning with widespread high clouds streaming in
ahead of disturbance out over the Eastern Pacific. High cloud will
persist across the region through the forecast period. Winds will
be mainly light over area terminals with a moderate seabreeze
around 10 kt expected over select terminals. 

Vicinity of KSFO...VFR conditions will prevail through the
forecast period with mainly light winds and streaming high clouds.
The typical onshore seabreeze will present itself around 21z this
afternoon at around 10-15 kt. Winds will ease once again after
sunset then veer offshore around midnight tonight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions will prevail through the
forecast period with mainly light winds and streaming high clouds.
Winds will turn offshore around midnight tonight.

&&

.MARINE...as of 8:51 AM PST Tuesday...Gusty northerly winds
expected today and into tomorrow that will produce hazardous
conditions with steep wind waves. A moderate northwesterly swell
will weaken briefly into midweek before winds and waves increase
again Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...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 Arena to Pigeon Pt 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: CW
MARINE: Anna


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