Small Craft Advisory 132, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1035 PM PDT THU JUL 7 2016

.SYNOPSIS...Onshore flow and a deep marine layer are expected to
persist the remainder of the week into the weekend. Low cloud
coverage will be widespread late night and morning hours, along
with patchy fog and local coastal drizzle. On Saturday, approach
of the tail end of a cold frontal system moving into the Pacific
Northwest will also bring the possibility of a few showers north
of about Pt Reyes. Temperatures will remain on the cool side for
this time of year with even inland areas seeing highs only in the
70s to lower 80s. A gradual modest warming trend then looks to be
in store for our area as we head into the first part of next week
as an upper level ridge of high pressure begins to slowly rebuild
over California.

&&

&&

.DISCUSSION...as of 08:24 PM PDT Thursday...Did a quick update
this evening to better reflect current reality with cloud cover
along the coast. Given the onshore flow, clouds are moving back
inland quick than previously thought. Additionally, included some
patchy fog along the San Mateo coast as Half Moon Bay is reporting
fog at two miles.

For the rest of tonight, very similar to the last few nights. The
N-S gradients are relatively weak while the W-E gradients are much stronger.
Therefore, the coastal clouds will continue to push back inland.
The marine layer will be nearly 2000 feet so inland penetration
will be good. Patchy fog and drizzle will also be possible along
the coast and locally inland. In fact, Oakland reported a trace
and Half Moon Bay reported 0.02 this morning. Would not be
surprised if a few places measured again Friday morning.

We are stuck in a very stagnant pattern so Friday will be similar
to Thursday. Morning clouds/fog will slowly erode back to the
coast. Sunny skies will prevail inland with patchy clouds along
the coast Friday afternoon.

The next weather item of note will be a weak boundary pushing
into NorCal Friday night/Saturday. Models continue to show a very
slight chance for light rain in our far North Bay areas. Current
forecast mentions rain and see no reason to change it.

&&

.PREV DISCUSSION...as of 3:00 PM PDT Thursday...

Friday night into Saturday, an unseasonably deep upper level low
will approach the coast of the Pacific Northwest with the tail
end of a cold front moving SE into far northern California.
Primary forecast issues for us are whether any shower activity
could make it southward into our area, the degree to which it
may further enhance the marine layer and associated coastal
drizzle Saturday morning, and the potential increase in onshore
winds Saturday afternoon and evening following its passage.

Based on consensus of latest NAM, GFS and ECMWF model output and
associated MOS PoPs, have introduced a slight chance of showers
Saturday coastal areas from about Pt Reyes northward. This may
well need to be adjusted as the time frame approaches, especially
if overall model trend in extending light precip chances
progressively a bit farther south continues. Do expect coastal
drizzle to be a bit heavier and more extensive Friday night and
Saturday morning as some lifting of the already deep and moist
marine layer occurs. Difficult to quantify this by specific
location, but describing in weather grid and forecast text as
areas of drizzle -- in contrast to patchy drizzle for tonight into
Friday morning. NAM and in-house 3 km WRF model output do indicate
winds along the coast and by the Bays will pick up Saturday
afternoon and evening, and result in locally breezy conditions.

Sunday and on into the first part of next week, a modest warming
trend is expected, primarily inland areas, as as an upper level ridge
of high pressure begins to slowly rebuild over California.

&&

.AVIATION...As of 10:35 PM PDT Thursday...Moderate onshore flow
and a deep marine layer will mean widespread MVFR/IFR CIGS through
the night with late clearing expected on Friday. Light westerly
winds overnight and into Friday morning, increasing on Friday
afternoon.

Vicinity of KSFO...IFR CIGS are forecast to continue through 16Z
Friday morning. MVFR CIGS are then forecast from 16Z until about
20Z on Friday before VFR conditions finally develop Friday
afternoon. Confidence moderate. Light west winds increasing to
20G28kt by late Friday afternoon.

SFO Bridge Approach...Similar to KSFO except earlier clearing on
Friday...probably by 18Z.

Monterey Bay Terminals...IFR CIGS forecast through the night with
possible LIFR CIGS from 12Z-16Z. IFR/MVFR CIGS likely to persist
for most of Friday except for a few hours of VFR conditions
in the afternoon. Confidence moderate.

&&

.MARINE...As of 8:29 PM PDT Thursday...High pressure offshore
will weaken tonight and friday...resulting in a temporary decrease
in northwest winds over the coastal waters. winds will then
increase again over the weekend as high pressure strengthens
offshore. a mixed northwest and southwest swell will continue to
move through the coastal waters through the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
             SCA...SF Bay until 11 PM

&&

PUBLIC FORECAST: MM
AVIATION: Dykema
MARINE: Dykema

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