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

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FXUS66 KMTR 190009

Area Forecast Discussion
National Weather Service San Francisco Bay Area
409 PM PST Wed Jan 18 2017

.SYNOPSIS...Widespread rain with gusty southerly winds can be
expected into the evening hours. Showers linger on Thursday but
in general there will be a break in the weather. Next front
arrives Thursday night into Friday with another round of wind and
rain. Lingering showers Saturday before the final front brings
more wind and rain Sunday before tapering to showers Sunday night
and Monday. Dry but cool Tuesday.

&& of 2:00 PM PST Wednesday...As expected rainfall
has returned to our region with KMUX indicating precipitation now
across most of our region. Please note that many of the higher
echoes being indicated are likely just bright banding and not
moderate to heavy rainfall. Rainfall totals to this point have
been light with Venado at the top over the past three hours with
just over half an inch.

Rainfall rates will increase through the remainder of the
afternoon and into the evening as a cold front eventually goes
across. Hourly rates of 0.20" to 0.40" and southerly gusts over 40
mph are possible for many locations during the frontal passage.
Rain will change over to showers starting this evening for the
North Bay and then quickly down to Monterey Bay overnight. By
tomorrow morning totals will range from 1.2" to 1.25" for most
urban spots with 1.5" to 3" for majority of higher elevation
areas. Hydro wise would expect reports of ponding on roadways plus
typical urban problem spots. However, do not expect creeks and
rivers to rise enough to cause flooding. CNRFC also updated its
numbers and now has the Russian River and Guerneville to monitor
stage by tomorrow afternoon. Also cannot rule out some thunder
tonight into early Thursday.

Scattered showers on Thursday will quickly give way to round two
as a second system approaches and brings more widespread rainfall
to our region. Timing has only slightly changed from previous
forecast packages with the bulk of the rain expected Thursday
night into early Friday. Guidance has rainfall amounts generally a
bit less with the second system, however the additional rainfall
will lead to another rise in rivers and streams. Rain will change
over to showers by Friday afternoon. Those showers will mostly
end by early Saturday morning. During this time snow levels will
drop down to around 3000 feet which will likely lead to some
accumulations for the higher local peaks. A few thunderstorms may
also pop up with this system.

A third and final system will bring widespread rainfall back to
the San Francisco and Monterey Bay Region for late Saturday into
Sunday. some disagreement with the models as far as how the
amounts of rain from this system will compare to the first two.
Current forecast has slightly lower values, however IVT and PW
amounts are actually higher than the second system. Regardless,
since it will be the third event in five days, any additional
rainfall will likely be problematic. Breezy southerly winds can be
expected once again.

Models start to diverge for next work week with the ECMWF/GEM bringing
across another system on Monday and showers into Tuesday. The GFS
is considerably drier and only indicates a few showers going into
Tuesday. For now went with higher PoPs but will hold off going
with very high values for now.


.AVIATION...As of 3:48 AM PST Wednesday...A cold front moving
across the state is bringing widespread rain and gusty winds to
the region. Periods of moderate to heavy rain and local vsbys
reduction are expected across area terminals this evening and
tonight. MVFR cigs will prevail with IFR cigs likely over the
North Bay tonight and locally elsewhere with accompanying
moderate/heavy showers. LLWS of 50-60 kt around 2000 ft will
remain possible through this evening. OAK and SFO have LLWS
mentioned. Did not include TSRA, but an isolated thunderstorm
remains a possibility...low confidence with regard to location
and timing. Rain will transition to more showers overnight into
early Thurs.

Vicinity of KSFO....MVFR cigs will prevail through much of the
period. IFR cigs possible with passing moderate to heavy showers.
LLWS of 50-60 kt around 2000 ft till 04Z. Wind shift from S to SW
more likely after 04Z. Strong and gusty winds will gradually ease

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR cigs will lower to MVFR after 06z
tonight. IFR cigs possible with passing moderate to heavy
showers. Strong and gusty winds will gradually ease overnight.

&& of 03:46 PM PST Wednesday...Strong and gusty
southerly winds will continue over the coastal waters through
tonight. the strong winds will result in hazardous conditions with
steep wind waves and rough seas. mariners are urged to use caution
if venturing to open waters. winds will decrease late tonight as
the storm lifts northeast but will increase again by friday as
another storm approaches. very large west swells will arrive later
this week with swells building as high as 26 feet friday and


     .Tngt...Wind Advisory...CAZ006-508>513-516>518-528>530
             Wind Advisory...CAZ505>507
             GLW...Pt Arena to Pt Reyes 0-10 nm
             GLW...Pt Reyes to Pigeon Pt 0-10 nm
             GLW...Pigeon Pt to Pt Pinos 0-10 nm
             GLW...Pt Arena to Pigeon Pt 10-60 nm
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 10 PM
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm from 10 PM
             SCA...Rough Bar Advisory for SF Bar
             SCA...Mry Bay
             GLW...SF Bay until 11 PM




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