Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 061237
Area Forecast Discussion
National Weather Service San Francisco Bay Area
437 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
.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
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
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 4:40 AM PST Tuesday... MVFR cigs expanding
across the Central Valley and interior SF/Monterey Bay valleys.
Currently have MVFR cigs at KSNS and KLVK ranging from
1200-2200ft. Expect to see gradual expansion towards KMRY into
sunrise. Cigs are spreading westward through the delta this
morning could spread towards and bring lowering cigs to KOAK...
and possibly KSFO as well. Otherwise, patchy dense fog posbl into
sunrise for KSTS and other inland valleys as well. VFR through the
daylight hours with some high clouds passing over head. Winds
generally light at the surface but stronger along the coast and
over the waters.
Vicinity of KSFO...VFR with a very slim chance of lower cigs
spreading southwestward from the Delta/Carquinez Strait area. WNW
winds up to 15knot today. East winds overnight into tomorrow
morning with high clouds over head.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Intermittent VFR/MVFR cigs spreading
towards the Monterey Bay from the Salinas Valley thru 17-18Z.
Otherwise, VFR today with winds 10 knot or less with high clouds
.MARINE...as of 04:31 AM PST Tuesday...Expect to see gusty
northerly winds continue along the coastal waters through today
and into tomorrow...producing hazardous conditions with steep wind
waves. a moderate northwesterly swell with a moderate period will
weaken into midweek. winds and waves increase thursday.
.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: Bell
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