Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 050014
Area Forecast Discussion
National Weather Service San Francisco Bay Area
414 PM PST Sun Dec 4 2016
.SYNOPSIS...A mainly dry cold front will approach northern
California Monday and Tuesday with seasonably cool temperatures.
There will be a slight chance of showers on Tuesday with the
front. Wednesday morning may be the coldest morning so far this
season with inland valleys around 30 degrees. Warm frontal rains
will be possible later Thursday into Friday.
.DISCUSSION...as of 1:53 PM PST Sunday...Some high clouds over
the Bay Area this afternoon with afternoon highs in the upper 50s
to around 60. The high clouds will keep overnight lows from
dropping too much as a mainly dry cold frontal boundary pushes
into northern California. Daytime highs will cool into the mid 50s
for Monday with high clouds and a cooler air mass in place.
A secondary cold front/short-wave will drop down on Tuesday with
steady rains confined to north of Cape Mendocino. There may be
just enough moisture and cold instability aloft to generate some
isolated showers across the area on Tuesday so slight chance pops
have been expanded for the Tuesday time frame. Any qpf with these
will be light and widely scattered in nature.
The coldest airmass of the season will be left in the wake of that
boundary and overnight lows by sunrise Weds morning could be the
coldest so far this season. Still a few days out so will hold off
on any frost/freeze type headlines as the leftover low clouds or
incoming high clouds could limit the amount of cooling.
Brief ridging will return on Wednesday with highs in the 50s as
high clouds begin to increase ahead of a warm advection pattern.
Confidence is increasing for warm advection rains to develop later
Thursday into Friday as a pacific jet approaches the region.
Early qpf numbers from the RFC shows 1-2.5 inches of rain
potential but at this time the best chances look to be focused
from the north bay southward to the Santa Cruz Mtns. Still a lot
of time to sort out timing and rainfall totals with this event but
the ecmwf has been consistent for at least the last four model
runs. With no strong cold advection not expecting heavy rain rates
but rather a prolonged period of soaking light to moderate rains
sometime later Thursday into Friday.
Low confidence beyond that with some type of break likely Friday
night into Saturday but then the models diverging on possible
continued systems later next weekend or early next week. Either
way no blocking ridges in sight and a nice moderately active start
to the rainy season.
.AVIATION...As of 3:48 PM PST Sunday...High clouds will continue
through this evening with cigs lowering to around 1000 feet around
06z-07z tonight as a weakening frontal boundary dissipates over
the region. Rain is not expected with this system but a moist
boundary layer will result in low cloud development overnight.
Moderate onshore flow will ease this evening becoming light and
variable overnight. Moderate confidence.
Vicinity of KSFO...VFR conditions expected this evening. MVFR cigs
expected to move in over area terminals around 06z-08z. Moderate west
winds between 5 to 15 kt expected through 03z. Winds will ease to
around 5 to 8 kt overnight. Moderate confidence with respect to
the return of the low clouds.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR conditions expected early evening.
MVFR cigs expected to move in over area terminals around 03z-06z.
West winds around 5 to 10 kt expected much of the period. Low confidence
with respect to the return of the low clouds. Thinking low clouds
may hold out a little long to around 06z.
.MARINE...as of 2:08 PM PST Sunday...Look for moderate
northwesterly winds to continue over the next several days
especially for outer water locations. A northwesterly swell
of 14 seconds of 8 to 10 feet will continue at least into
.Tngt...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...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Rough Bar Advisory for SF Bar until 3 AM
PUBLIC FORECAST: RWW
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