Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 202346

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

.SYNOPSIS...Scattered showers are expected to continue today in
the unstable airmass behind the front that moved through this
morning. In addition, isolated thunderstorms will be possible. A
few showers will then linger 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 into Monday with dry conditions returning by Tuesday.

&& of 2:10 PM PST Friday...showers continue to move
across the area in the unstable post-frontal airmass. There have
also been recent reports of pea-sized hail and thunder across
portions of the East and South Bay associated with a robust line
of showers currently moving across that area. Expect showers to
persist through this evening and slowly taper off by Saturday mid
day. At this time, showers will likely be ending with a bit of a
break in precipitation for a good portion of the region through
the rest of the day.

The next system in this series remains on track to impact the
area from late Saturday into Sunday morning. This system appears
to have a deeper moisture tap with PWAT values forecast to range
between 1 to 1.25 inches. Given this, expecting rainfall amounts
to be greater than the previous two systems which will likely
lead to a greater threat for flooding issues. Additional rainfall
amounts from Saturday into Sunday will range from 0.75 to 1.50
inches in most urban areas and upwards of 2 inches in the North
Bay Valleys. Meanwhile, the coastal ranges and North Bay Mountains
will likely see 2 to 4 inches with isolated amounts upwards of 5
inches. A Flash Flood Watch has been issued for the entire CWA
effective from midnight Saturday through 6 pm Sunday. Considering
a few creeks went to flood stage with last night`s storm, additional
moderate to heavy rain is likely to cause flooding issues. Along
with the additional rainfall, southerly winds will also increase
and become gusty at times ahead of the frontal boundary that will
sweep through late Saturday night into early Sunday morning. A
High Wind Watch is in effect for the entire CWA for the time frame
from late Saturday evening through Sunday morning. The areas most
likely to see the strongest winds will be the coasts and hills,
however, with the frontal passage, strong winds are possible

Showers will then likely linger into Sunday night and even through
much of the day Monday as the main mid/upper level low drops
southward down along the northern California coast. By Tuesday, the
trough will shift inland while a ridge begins to develop off of
the West Coast. This ridge will maintain dry weather conditions
through the remainder of next week with temperatures near seasonal


.AVIATION...As of 3:45 PM PST Friday...A moist and unstable
atmosphere will maintain showery conditions across the region.
Showers will be hit and miss in nature therefore have kept -SHRA
in the TAFs through this evening. Showers will ease overnight
hence the VCSH through the remainder of the TAF period.
Borderline VFR/MVFR Cigs will prevail. Period of gusty
southwesterly winds will continue through this evening then ease

Vicinity of KSFO....Gusty southwesterly winds will prevail through
late tonight. Showers will continue through this evening with both
winds and showers gradually diminishing overnight. Borderline
VFR/MVFR cigs will also continue.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Gusty southwesterly winds will prevail through
this evening. Showers will continue through this evening with
both winds and showers gradually diminishing overnight. Borderline
VFR/MVFR cigs will also continue.

&& of 2:40 PM PST Friday...Moderate and gusty west
winds will prevail across the coastal waters through tonight in
the wake of the cold front that passed through earlier today.
Winds will increase again Saturday evening as another frontal
system approaches. Very large swells arrived today with swell
heights building to 25 to 30 feet by tonight and Saturday. Rogue
waves of 30 feet or greater are possible during this timeframe.


     .Tngt...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
             SCA...SF Bay until 10 PM




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