Forecast Discussion
Forecast Discussion for MTR NWS Office
FXUS66 KMTR 112336

Area Forecast Discussion
National Weather Service San Francisco Bay Area
336 PM PST Tue Dec 11 2018

.SYNOPSIS...A weak system may bring a few showers to northern Sonoma
County tonight. However, for the most part our forecast area is
expected to remain dry and seasonably cool through Thursday.
Another disturbance will bring rain to the region on Friday and
Friday night, especially for areas north of the Golden Gate. A
potentially wetter system will then bring widespread rain to the
region on Sunday.

&& of 01:50 PM PST Tuesday...The dense fog from
this morning was slow to burn off, but eventually gave way to
sunny skies this afternoon. The last bit of fog is hanging on in
the vicinity of SFO. Given the foggy start temperatures were slow
to rise, but have gradually warmed up this afternoon.
Temperatures are generally running in the 50s to mid 60s.

A weak cold front currently off the PacNW Coast is still ontrack
to drift southward toward the North Bay tonight. The general trend
over the last few days has be drier and much weaker with the cold
front. In fact, some of the latest hi-res models do not bring much
in the way of precip to the North Bay anymore. There could be a
few sprinkles over far northern Sonoma county. Fog will also be
possible across the N and E Bay Valleys tonight, but nothing like
this morning.

High pressure re-builds on Wednesday in response to a digging
trough over the Pacific. Dry weather with slightly warmer
temperatures are expected Wed and Thur. Some night and morning
patchy fog will once again be possible.

High pressure shifts eastward by Friday as another cold front
approaches from the NW. Latest timing brings some pre-frontal
showers early Friday, but rain chances increase through the day.
Models are at odds on how much rainfall with the Friday cold front
as the GFS continues to be dry and the ECMWF is much wetter. Will
lean toward the ECMWF given recent performances and bring rain
chances through the entire forecast area Friday into Saturday. A
few lingering showers are possible Saturday during the day, but
likelihood is low. The strongest system of the bunch will impact
the region Sunday into Monday. Atmospheric river guidance
indicates a decent moisture plume putting this in the Moderate
Category for ARs. Rainfall will be greatest over the North Bay and
terrain favored locations. Would like to see some better model
consensus on the details, but regardless it looks like a good
beneficial rain for the region.

&& of 03:36 PM PST Tuesday...For 00Z tafs. VFR
conditions through tonight with increasing high clouds as a weak
cold front approaches. Possible fog development again around the
North and East Bay terminals overnight. Low clouds may also
develop at other area terminals overnight and through tomorrow
morning. Timing and the extent of fog/low cloud development is
uncertain and overall confidence remains low. VFR conditions
forecast to return late tomorrow morning/early in the afternoon.
Winds will remain generally light through the period.

Vicinity of KSFO...VFR through tonight before possible return of
IFR/LIFR cigs overnight. Expecting winds to turn onshore late this
afternoon and remain light overnight. Overall confidence on cigs

SFO Bridge Approach...similar to KSFO, may see more cloud
development over the approach.

Monterey Bay Terminals...VFR with increasing high clouds.
Potential for low clouds and reduced vis overnight, but confidence
is low.

&& of 02:47 PM PST Tuesday...North to northwest winds
will diminish briefly this evening before increasing again to
moderate levels during the overnight. Wind speeds will diminish
Wednesday night into Thursday and become southerly. However, a
building northwest swell will impact the coastal waters late in
the week resulting in hazardous conditions. A much more
significant northwest swell is forecast to impact the region
Sunday into Monday.

A larger northwest swell with a moderate period of around 16
seconds will arrive over the coastal waters late Wednesday night
into Thursday. Another reinforcing swell train arrives Friday into
Saturday with the potential need for a High Surf Advisory. A much
more significant northwest swell is forecast to impact the region
by Sunday afternoon and build into Monday morning. Swell heights
of 18 to 24 feet at around 20 seconds will result in breaking
waves in excess of 30 feet would be possible. Thus, the need for a
High Surf Warning will be evaluated as the event draws closer.


     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 9 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 3 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm




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NWS MTR Office Area Forecast Discussion