Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 230400
Area Forecast Discussion
National Weather Service San Francisco Bay Area
900 PM PDT Wed Mar 22 2017
.SYNOPSIS...Clearing and drying trend overnight through Thursday.
Widespread rainfall and stronger winds return to the northern
portion of the region late Thursday night and will spread
southward during the day Friday. Dry conditions return for most of
Saturday with another weather system forecast to push through
starting Sunday night into Monday.
.DISCUSSION...as of 9:00 PM PDT Wednesday...As expected shower
activity quickly winding down as the sun has set. Still a stray
shower or two on radar but those should end before midnight.
Thursday still looks on track to be our break day with some
sunshine and seasonably cool highs in the lower 60s.
00z nam and gfs look on track with the next storm bringing rain
into the north bay about 24 hours from now. Then the front will
slowly shift southward Thursday night into Friday setting the
stage for a wet Friday morning commute. The rain wont reach the
Central Coast until Friday afternoon and evening but then drop
steady rains from the Santa Cruz mountains southward to the Santa
Lucia range of Big Sur as an upper wave and surface low develop
along the boundary and slow its southward progression. QPF numbers
remain on track as described below. Precip ends in the North Bay
Friday night but showers linger from the Golden Gate southward
until about 12z Saturday.
Saturday looks to be a dry and cool day (not too different than we
are expecting for Thursday). Models have been hinting that the
next storm due to arrive late Sunday could be trending stronger as
well but the 00z gfs and ecmwf have not arrived. If the trends
hold true we`ll see another cold and wet storm to wind out the
weekend and start the work week. The system looks cold with not as
much moisture as the Friday system. Behind that things should dry
out for a while.
.PREV DISCUSSION...as of 3:00 PM PDT Wednesday...KMUX radar shows
scattered showers continuing across our region -- especially for
the southern third of the CWA. Returns indicate a few moderate
cells so would expect a few are dropping small hail. Showers will
greatly diminish once the sun goes down, and additional
accumulations will mostly be under a tenth.
Dry weather will return for tonight through the majority of
Thursday before another system from the north moves through and
brings widespread rainfall back into the picture. Models have been
advertising this system for nearly a week and the latest guidance
has only slightly wavered from previous runs. Now looks like rain
will move into the North Bay Thursday night, down to SF Bay Friday
morning and to Monterey Bay starting around noon. However, the
main story will be the moderate to heavy band of rain associated
with a surface front that will go through later than the initial
round of rain. That band could produce high rain rates for a brief
period possibly leading to some urban and small stream issues. At
the same time southerly winds will be on the increase as the front
approaches. Gusts in many urban locations of 25 to 35 mph can be
expected. Values to 50 mph are possible above 1,500 feet. Guidance
has slightly trended downward so at this time do not expect to
issue wind advisories.
Rainfall amounts have only slightly changed from previous forecast
packages. Still looks that the best IVT numbers (and longest
duration) will focus on the North Bay with widespread 1.5-3"
expected (locally 4+" for the North Bay Mountains). Similar values
can be expected for the SC Mountains plus the Santa Lucias.
Around SF Bay generally 2/3" to 1.5" is forecast with mostly less
than 2/3" from the Santa Clara Valley southward.
Behind the front scattered showers are possible into early
Saturday. This will be followed quickly by another system that
will again move north-to-south late Saturday night through
Sunday. This feature will be the weakest of the week and rainfall
totals should be generally under 1/2" for most urban locations.
A ridge of high pressure will build behind that system and bring
warmer and drier conditions back to our region for most of next
week and possibly through the following week.
.AVIATION...As of 5:15 PM PDT Wednesday...A few showers continue
over the interior Santa Clara and San Benito counties but only
sct-bkn040 over the terminals. Clouds decreasing after 03Z. Patchy
low clouds reform late tonight and we cannot rule out brief local
Vicinity of KSFO...VFR. West winds 15-20 kt decreasing after 04Z.
SCT020 12Z-16Z but cannot rule out a brief cig at BKN020.
SFO Bridge Approach...Same as KSFO.
Monterey Bay Terminals...VFR with scattered clouds through 05Z.
Low clouds forming over the hills will spread into MRY and SNS after
05Z leading to MVFR cigs 05Z-16Z.
.MARINE...as of 08:50 PM PDT Wednesday...High pressure off the
southern california coast will weaken tonight resulting in
decreasing northwest winds. the winds will become southerly and
increase on thursday a ahead of the next system. winds will
increase during the day thursday. winds will switch to the
northwest friday but another system may impact the waters on
.Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 9 PM until 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
PUBLIC FORECAST: RWW
AVIATION: W Pi
MARINE: W Pi
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