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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 181759

Area Forecast Discussion
National Weather Service San Francisco Bay Area
959 AM PST Fri Jan 18 2019

.SYNOPSIS...Shower chances will continue across the North Bay on 
Friday and Saturday as the storm track shifts north. A weak
boundary will move into the SF Bay on Saturday morning, bringing 
a chance of showers to most of the Bay Area. Dry conditions are
anticipated elsewhere through Saturday. More widespread light 
rain is forecast for Sunday as a Pacific storm system moves
through the area. Dry and mild weather is expected to develop on 
Monday and continue through the remainder of next week.

&& of 9:26 AM PST Friday...KMUX radar indicated 
some weak echos associated with light rain showers earlier this 
morning across the North Bay. The showers were sufficient enough 
to register some measurable rainfall, including both the Napa and 
Santa Rosa Airports where 0.01" and 0.02" were recorded, 
respectively. The latest run of HRRR suggests light rain showers 
to continue off/on in the North Bay, primarily focused during the 
the afternoon and evening hours. Most locations south of the 
Golden Gate can generally expect dry conditions for the day on 
Friday before light rain chances nudge upward after sunset and for
the overnight hours. High temperatures are forecast to rise to 
middle 50s to middle 60s across the region this afternoon, with 
the warmest locations in the Salinas Valley. The short-term 
forecast remains on track and do not anticipate making any major 
updates to the grids at the present. For additional details beyond
Day 1, please refer to the previous discussion section.


.PREV of 03:20 AM PST Friday...KMUX radar indicates a 
few light showers over the coastal waters, which appear to be 
dissipating before they move inland. These showers are not being 
resolved by models but expect any showers which manage to reach 
land to be light. Extensive cloud cover has kept temperatures 
fairly mild with current temperatures in the mid 40s in the North 
Bay valleys to the mid 50s near the SF Bay shoreline. Cloud cover 
is preventing fog from forming apart from isolated locations. 

An upper level ridge forming just offshore will build along the
California Coast on Friday. This will shift the storm track to the
north with heavy rainfall expected in Oregon and far northern 
California Friday through Saturday. Moisture will move far enough
south to bring scattered light showers to the North Bay for much 
of Friday. A weak boundary is then forecast to move southeast into
the greater Bay Area Saturday morning before dissipating. This 
will bring a chance of light rain as far south as San Jose. Light 
showers will continue across the North Bay through Saturday. Up to
a half inch of rain is anticipated through Saturday night in 
portions of the North Bay, tapering to only a few hundredths 
around the Golden Gate. High temperatures Friday and Saturday 
will be slightly above normal in our southern regions with low to 
mid 60s expected. Thicker cloud cover and light precipitation will
keep the North Bay cooler with highs in the upper 50s to near 60.

An upper level trough will push the ridge east and bring a chance
of rain to the entire area on Sunday. A cold front will push
through the area Sunday morning into Sunday afternoon, with 
precipitation along the front. The front is expected to weaken as 
it passes through the area, and moisture appears limited with PWAT
remaining under an inch. Showers will continue behind the front 
as the cold core of the upper low moves overhead. Rainfall totals 
with this system will be light, with an additional half inch 
possible in the North Bay with less than a quarter inch elsewhere.
Behind the cold front, northwest winds could become breezy near 
the coast and in the higher terrain as surface high pressure 
builds to the west and the surface low deepens over the Great 

The pattern will transition to much drier beginning on Monday. High
pressure will strengthen over the East Pacific and gradually shift
east. By Thursday, the ridge will become highly amplified with 
the storm track shunted north into Alaska and the ridge axis 
along the coast. Models are in excellent agreement about the 
ridge remaining anchored in place through at least the end of 
next week. This will result in no chance of precipitation during
the extended. Dry weather and mostly clear skies will create seasonably
cool nights, while high temperatures will be above normal.

&& of 9:53 AM PST Friday...for 18Z TAFs. Showers have
ended, but mid-high cigs remain. A few weak disturbances will pass
through NorCal bringing a chance for some showers, but most likely
for the North Bay and OAK/SFO. Winds will be generally light.

Vicinity of KSFO...Light winds and mid level cigs through this
evening. A few showers may impact the terminals overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR conditions expected through the
period. Light winds.

&& of 9:57 AM PST Friday...Buoys continue to show
moderate-large swell with a moderate period. Breaking waves of 20
to 30 feet are possible today. A High Surf Warning remains in 
effect until 5 PM today. These large breaking waves will lead to 
increased wave run- up on beaches with waves topping and washing 
over large rocks and jetties. These conditions may also produce 
localized coastal flooding of vulnerable locations, especially 
early this morning during high tide. Use extreme caution near the 
surf zone as these large waves will be capable of sweeping people 
into the frigid and turbulent ocean water. Cold water shock may 
cause cardiac arrest, and it also can cause an involuntary gasp 
reflex causing drowning, even for a good swimmer. The surf zone 
will be very dangerous due to strong currents and powerful 
breaking waves. 

&& of 09:51 AM PST Friday...Swells will continue
gradually diminish through the day, but still remain hazardous
through this evening. Of greatest concern will be near the
immediate coastline, harbor entrances and the  San Francisco Bar.
Conditions will improve tonight and into the  weekend as the
swells continue to diminish.


     .Tday...High Surf Warning...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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