Small Craft Advisory 179, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
339 AM PDT SUN AUG 21 2016

.SYNOPSIS...Slightly cooler than normal temperatures are forecast
over the next few days, along with widespread night and morning
low clouds. Smoke will continue to have an impact on air quality,
but mainly across areas to the south and east of Monterey Bay. Modest
warming expected by midweek. Long range forecast maintains a dry
and seasonable weather pattern.

&&

.DISCUSSION...As of 3:35 AM PDT Sunday...A complex weather
pattern is in place over California and surrounding areas early
this morning with an upper level high pressure ridge to our north
and east and a weak upper low to our southwest. In between these
systems an easterly flow aloft continue to advect high level
moisture across our area and offshore. A small upper level
disturbance offshore has triggered an area of convective
precipitation out along 130W between 35-40N with several lightning
strikes detected in that area since midnight. The GFS and NAM had
been inconsistent in forecasting both location and timing of
isolated convective precipitation, but the latest output from
these two models indicate isolated convective precipitation
approaching the Sonoma county coast tonight as the upper low moves
slowly to the east. Therefore, have increased POPs slightly over
our northern coastal waters tonight, but do not yet feel there is
sufficient model consistency to explicitly add shower/thunderstorm
chances to our forecast. If the convection currently offshore
persists through the morning hours, and if the 12Z model runs
continue to indicate at least isolated precipitation near the
North Bay coast, then forecast confidence should be sufficient to
add a mention of shower/thunderstorm chances for tonight.

Otherwise, no significant changes are expected in our weather over
the next few days. The Fort Ord profiler shows a slight reduction
in the depth of the marine layer overnight, but onshore surface
pressure gradients have increased slightly. All model guidance
indicates that daytime temperatures will remain slightly cooler
than normal through at least Monday and possibly into Tuesday.
And, we can expect continued widespread night and morning low
clouds. Modest warming is anticipated by midweek as the weak upper
low offshore finally moves inland and to our east and an upper
ridge builds just offshore.

Latest HRRR model output continues to indicate that smoke
concentrations from several wildfires across California will
continue to decrease from north to south across much of our
forecast area over the next 24 hours. So we can generally expect
improving air quality across the San Francisco Bay Area and as far
south as Monterey Bay. However, areas in closer proximity to the
Soberanes and Chimney fires will continue to see higher smoke
concentrations and poor air quality.

&&

.AVIATION...as of 10:35 PM PDT Saturday...Marine layer around
1800 feet tonight with light onshore flow. Satellite image shows
stratus through the Golden Gate into OAK but not at SFO. With more
of a westerly flow the stratus should get into SFO and much of the
SFO Bay Area after 10Z.

Vicinity of KSFO...MVFR/IFR cigs after 10Z clearing after 17Z.

SFO Bridge Approach...MVFR/IFR cigs after 10Z clearing after 18Z.

Monterey Bay Terminals...IFR conditions through 18Z at SNS and 19Z
at MRY.

&&

.MARINE...as of 10:35 PM PDT Saturday...A weak high will develop
off the southern California coast. This will bring light northwest
winds to the southern waters while winds remain west to southwest
over the northern waters. Northwest winds and swell will increase
by tuesday the eastern pacific high moves closer to the west
coast. Mixed seas with a short period northwest swell and a longer
period southerly swell will continue through much of the forecast
period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...None.

PUBLIC FORECAST: Dykema
AVIATION: BAM
MARINE: Sims

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook and twitter at:
www.Facebook.com/nwsbayarea
www.twitter.com/nwsbayarea