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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 170351

Area Forecast Discussion
National Weather Service San Francisco Bay Area
851 PM PDT Sun Jun 16 2019

.SYNOPSIS...Warming is forecast for Monday and Tuesday as high 
pressure strengthens over California, and onshore flow weakens. 
However, warming at coastal areas will be limited due to 
persistent onshore winds. Seasonable temperatures, along with 
areas of night and morning low clouds, are forecast through the 
end of the week.


.DISCUSSION...As of 8:50 PM PDT Sunday...A slight reduction of
onshore flow today resulted in modest warming across inland
portions of the San Francisco Bay Area. Otherwise, there was
little change from yesterday and afternoon highs were anywhere
from 5 to 10 degrees cooler than seasonal averages in most areas.

More widespread and significant warming is forecast by Monday as 
an upper ridge, currently centered over the Eastern Pacific along 
140W, noses eastward over northern California. The persistently 
deep marine layer should finally begin to compress by Monday, 
allowing for earlier inland clearing. In addition, onshore flow 
will continue to gradually subside. These developments will allow 
for anywhere from 5 to 12 degrees of warming tomorrow, with most 
warming expected in the hills and inland valleys. Over the past 
few days the models have been consistently too warm, and it looks 
like that may be the case once again tomorrow. A forecast update 
was recently completed to reduce tomorrows max temps in most areas
by 3 to 5 degrees. 

Little change is forecast on Tuesday, except perhaps a degree or
two of additional warming. Although night and morning low clouds
won't be as extensive across inland areas over the next few
days, lack of offshore flow will mean persistent marine layer 
clouds in coastal areas, and thus lack of significant coastal 

The upper trough will begin to weaken over California by midweek
as an upper trough over the Gulf of Alaska moves into the Pacific
Northwest. Cooling may begin as early as Wednesday, although the
magnitude of cooling looks to be slight that day. More significant
cooling is then forecast for Thursday as the upper trough digs
south into the northern Great Basin, forcing a retreat of the
upper ridge back offshore. Temperatures are then forecast to
rebound slightly on Friday and settle in at near seasonal averages
as we move into next weekend. 

&& of 4:305PM PDT Sunday...Marine layer continues 
around 2000 feet but is expected to compress overnight. Onshore 
gradient has turned more northwest as the SFO-ACV pressure 
gradient has increased to 4.2 mb. This will result in a later 
intrusion of clouds into the Bay Area. Latest tafs have backed off
the timing of the low cigs for a couple of hours. Cloud bases are
expected to be lower tonight. 

Vicinity of KSFO...IFR cigs after 06Z with bases 800-1000 feet. 
West winds 15-18 kt decreasing after 04Z. 

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Widespread MVFR cigs after 02Z lowering
to IFR after 05Z. 

&& of 04:22 PM PDT Sunday...Breezy northwest winds
across most of the waters today, with locally stronger, gusty
winds across the outer waters north of Point Reyes and through the
Golden Gate gap to Angel Island.  Steep fresh northwest seas.


     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay until 8 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm




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