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FXUS66 KMTR 210624

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1024 PM PST Fri Jan 20 2017

.SYNOPSIS...Scattered showers will continue tonight into Saturday 
morning with another, likely wetter system arriving late Saturday
into Sunday. Given the antecedent conditions from recent rainfall,
this system will have the potential to result in additional 
flooding concerns across portions of the region. Showers will then
linger behind this cold front through Monday with dry conditions 
returning later next week.

&& of 9:00 PM PST Friday...A 517MB upper low
is approximately 300 miles offshore of Washington state late this
evening. The surface cold front associated with this system swept
through the area overnight last night, which brought another round
of rainfall and gusty winds. 24 hour rainfall totals were topped
by the higher terrain of the Santa Cruz mountains, where 2 to
nearly 4 inches of rain fell. Other coastal ranges saw locally
higher amounts, while urban valley locations picked up 0.5-1.5".
More impressive were the winds, with gusts over 60 MPH recorded
in Big Sur, at Buoy 14, and near the Los Gatos Raws, while closer
to sea level, KSFO observed a gust to 49 MPH.

Numerous rain showers have moved across the state today in
response to the unstable environment left in the wake of the
surface cold front that is currently pushing into the Great Basin
and extreme southwest California. Embedded convection within this
unstable environment also intensified some of these storm cells
into thunderstorms, with reports of gusty winds, small hail, and
brief heavy downpours coming in throughout the day and into this
evening. A broad cumulus field south of the core of the
aforementioned upper low still remains upstream, so additional
rain showers are expected through the night and into tomorrow
morning. That said, convective parameters taper off further into
this evening, so the strongest storm cells are now over for the
local area.  

A very large swell train will traverse the coastal waters and
bring hazardous conditions along our beaches tonight and
tomorrow. Large sneaker waves (up to 30 foot) will be mixed in
with smaller wave sets and can knock unsuspecting people into the
frigid, turbulent ocean. Remember to never turn your back on the

The last in a long series of wet storms so far this month is set
to arrive late Saturday into Sunday morning. This system is
anticipated to be stronger than the previous system that just
moved through the area, both in terms of rainfall accumulations
and winds. Rainfall amounts will range from .75" to 1.5" for most
urban valleys, with locally up to 2" in North Bay valleys, while
coastal ranges will see 2-5" due to orographic effects. Given the
wet antecedent conditions and battered storm infrastructure from
this extremely wet few weeks, any additional rainfall will bring
greater flooding and mudslide threats than typically anticipated
for a similar storm. A flash flood watch is in effect for the
entire forecast area from Sonoma to Monterey counties through the
duration of the storm. In addition, the strong winds will likely
cause more downed trees and sporadic power outages as trees and
power poles will tip easier in the supersaturated soils. A high
wind watch is in effect for Saturday night as the surface front
shifts across the region. The strongest winds are expected over
the coastal waters, along the coast, and over our highest terrain.
Winds gusts of 60 mph or greater are possible, with localized
gusts to 70 mph not out of the question over Big Sur and other
coastal peaks. Post frontal rain showers will linger through
Sunday night and into the day Monday.

Models show a dry weather pattern returning to the area late Tuesday
as a ridge of high pressure moves into the vicinity. There is some
uncertainty for how long this will last, as latest model shows do
show a weak disturbance entering the area on Wednesday. A longer
duration of dry weather will then set up for late next week into
the foreseeable future.


.AVIATION...As of 10:25 PM PST Friday...A continuing moist and
unstable atmosphere will maintain showery conditions across the
region. Showers will be hit and miss in nature, and gradually
diminish during the day on Saturday. Winds may become temporarily
gusty, and ceilings and visibilities reduced, in the vicinity of
heavier showers. Also, can't completely rule out the possibility
of a thunderstorm. 

Vicinity of KSFO....Scattered showers will continue to pass
through the area overnight and Saturday morning, then diminish.
Winds will generally be west 8 to 15 kt, but possibly gusting to
20 to 25 kt vicinity of heavier showers along with temporary
reduction in ceilings and visibilities. Can't completely rule out
the possibility of a thunderstorm.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Scattered showers will continue to pass
through the area overnight and Saturday morning, then diminish.
Winds will generally be less than 10 kt, but possibly gusting to
20 to 25 kt vicinity of heavier showers along with temporary
reduction in ceilings and visibilities. Can't completely rule out
the possibility of a thunderstorm.

&& of 9:06 PM PST Friday...Moderate and locally gusty
west winds will prevail across the coastal waters tonight along
with scattered showers and possible thunderstorms. Winds will
increase again Saturday evening as another strong frontal system
approaches. Very large swells arrived today with swell heights
building to 25 to 30 feet by later tonight and Saturday. Occasional
wave heights of 30 feet or greater are possible during this


     .Tngt...High Surf Warning...Entire coastline from Sonoma to 
                                 Monterey county
             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
             SCA...SF Bay




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