NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 181747

Area Forecast Discussion
National Weather Service San Francisco Bay Area
947 AM PST Tue Dec 18 2018

.SYNOPSIS...High Surf Advisories continue today. Otherwise a weak
warm front will bring light rain to the far North Bay. Drying
trend Wednesday and Thursday all areas with the next weak front
bringing some light rain, mainly to the North Bay Thursday night.
Drying trend returns Friday and Saturday before rain chances
increase Sunday into Monday.

&& of 8:42 AM PST Tuesday...Visible satellite shows
high clouds continuing to stream over the San Francisco Bay Area
and Central California Coast this morning. There were some
isolated locations in the North Bay that have managed to squeeze a
few one-hundredths of an inch of rain earlier in the day as they
have been on the far southern edge of a system that is presently
impacting northern California, Oregon, and Washington State.
Locations south of the Golden Gate will remain dry today as a
ridge begins to strengthen off the southern California coast. Highs
this afternoon will be rather seasonable across the region,
ranging from the upper 50s in the North Bay to the low/mid 60s in
the Salinas Valley. The short-term forecast remains on track at
this time; for additional details beyond today, please refer to
the previous discussion.


.PREV of 3:07 AM PST Tuesday...Short term concern is
patchy dense fog. So far its mainly confined to the North Bay with
Sonoma, Napa and Novato all reporting overnight. Nighttime
microphysics on the Goes-17 shows some patches over the southern
Salinas Valley as well with more valley fog formation likely
between now and sunrise.

Upper and surface pattern features high pressure over the region
at this time but its a dirty ridge with lots of high clouds
spilling over in well defined anti-cyclonic flow aloft. 588 dm
ridge centered west of Point Conception with moist boundary
slamming into Cape Mendocino. Models bring rain shield as far
south as northern Sonoma county today, to about the 576 dm
contour. Pretty high confidence for light rain along the Mendo
county line but little precip south of Santa Rosa with amounts on
the light side across northern Sonoma county. Elsewhere filtered
sunshine with highs upper 50s and lower 60s today.

Dry conditions region-wide on Weds and Thursday as high pressure
noses across the Bay Area. Daytime highs seasonably mild in the
upper 50s and 60s with fairly mild overnight lows in the 40s.

Pattern remains progressive with another front poised to move
towards Cape Mendocino Thursday night. This should bring a quick
shot of light rain, mainly for the North Bay Thursday night.
Similar to recent trends the front will weaken and fall apart
south of I-80.

Lingering clouds, especially for the North Bay on Friday but
a return of dry and seasonable weather into Saturday.

The euro brings a shot of light/moderate rain Sunday and then
again later Monday into early Tuesday while the gfs has it focused
mainly on Monday as a one time storm. Ensemble and model blend
data is focusing on Monday right now as the best chance for an
organized rain storm. Will see if the latest euro is the leading
indicator or an outlier as model specifics beyond about 5 days
have been changeable as of late in this moist onshore flow.

Long range signals still look good for continued wet and active
weather beyond Christmas with the PNA signal forecast to turn
negative implying troughiness along the West Coast.

&& of 09:45 AM PST Tuesday...IFR/LIFR conditions
impacting the North Bay terminals this morning as a weak frontal
boundary has stalled over northern California. Look for these
conditions to persist through much of the day with VFR conditions
for the remainder of the region. High clouds will stream inland
ahead of the aforementioned frontal system with generally light
winds. There is a possibility of low clouds, developing between
09-15Z Wednesday over the northern portion of the region. This
may result in MVFR, or locally lower, conditions early Wednesday
morning for these locations. Confidence is low to moderate beyond
06Z Wednesday.

Vicinity of KSFO...VFR conditions and light winds.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions and light winds.

&& of 09:45 AM PST Tuesday...Hazardous beach
conditions will persist along the shoreline through this afternoon
as a large, long period northwest swell continues to gradually
subside. Breakers of 15 to 25 feet will remain possible, locally
larger at favored break points along the coast. In addition, large
wave run up is possible along the coast, particularly during high
tide. As a result, a High Surf Advisory remains in effect through
this afternoon. A different large, long period northwest swell
train will move into the waters late Wednesday into Thursday with
forerunners arriving earlier in the day Wednesday producing
increased risk of sneaker waves. Do not turn your back on the
ocean and stay aware of your surroundings if visiting the coast.

&& of 09:45 AM PST Tuesday...Locally gusty northwest
winds will develop along the Big Sur coast this afternoon and
evening. A weak front will bring light southerly winds to the
northern waters today. Otherwise generally light northwest winds
are expected through Wednesday. A large long-period swell will
slowly subside today but will increase again Wednesday night as
another swell train approaches.


     .Tday...High Surf Advisory...CAZ006-505-509-529-530
             SCA...Mry Bay
             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 Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Rough Bar Advisory for SF Bar




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NWS MTR Office Area Forecast Discussion