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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 240557

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1057 PM PDT Sun Jun 23 2019

.SYNOPSIS...A cooling trend will get underway tomorrow and
continue through midweek, with temperatures forecast to cool by 10
to 20 degrees by Wednesday. In addition, expect an increase in 
night and morning low clouds over the next few days. Temperatures
will warm a bit late in the week and into next weekend, but remain
near or slightly below seasonal averages. 


.DISCUSSION...As of 8:35 PM PDT Sunday...Today's weather was very
similar to Saturday. Afternoon highs were a few degrees warmer 
than normal in coastal areas and up to 10 degrees warmer than 
normal inland. 

The first signs of the impending cooling trend are already
evident, with stronger seabreeze winds in many areas this evening
compared to last evening. Also low clouds near the ocean are more
widespread this evening compared to last evening, and we will 
likely see fog develop in coastal areas overnight and persist into
early Monday. A forecast update was completed earlier this 
evening to add patchy fog to coastal areas from late this evening
through mid morning on Monday. Patchy dense fog is also possible. 
The marine layer is still rather shallow and so fog and low clouds
likely won't develop very far inland yet tonight.

GOES-West water vapor satellite imagery shows an upper trough
off the coast of the Pacific Northwest this evening. This trough
is forecast to deepen along the West Coast through midweek,
resulting in much cooler temperatures across our area, especially
inland, by Wednesday. The models agree that we can expect anywhere
from 3 to 8 degrees of cooling for each of the next three days as
the upper trough brings a cooler airmass into our area, and we 
also experience increasing marine air influence due to a 
deepening marine layer and stronger onshore flow. High 
temperatures were as much as 8 degrees warmer than normal today 
will be as much as 12 degrees below normal by Wednesday. In 
addition, expect more widespread night and morning low clouds and 
fog by Monday night, and especially Tuesday night.

The upper trough is forecast to weaken late in the week and into
next weekend. At the same time, an upper ridge is forecast to
strengthen over the Desert Southwest. The result will be slightly
warmer temperatures across our region by Friday and Saturday. 
However, temperatures will likely remain slightly cooler than 
normal through next weekend given that both the EPS and GEFS
maintain a weak trough near the West Coast through the end of the
extended forecast period. Beyond that, the EPS and GEFS agree that
the mean trough position will retrograde, possibly allowing for a
more robust warmup over California as we approach July 4th.  

&& of 11:00 PM PDT Sunday...For 06z TAFs. A shallow
marine layer is beginning to expand in coverage this evening, with
stratus currently along the coast from the Marin coastline south 
through the Monterey Bay terminals. High pressure over the area 
will weaken which may result in a slight increase in the marine 
layer depth tonight. As such some of the terminals around SF Bay 
and the North Bay should see more widespread low clouds developing
towards sunrise. Along the coast, once again will likely see 
reduced visibilities along with LIFR cigs through Monday morning 
as the marine layer remains compressed with observed cloud bases 
near 500-800 feet, lowering expected as the night progresses. The
stratus layer is expected to remain fairly thin resulting in 
clearing skies Monday morning with VFR developing at all TAF 

Vicinity of KSFO...VFR conditions this evening and overnight are
expected. A brief period of MVFR cigs may develop around sunrise
and continue through 16-17z, but confidence is low due to the
shallow depth of the marine layer. WNW winds overnight 10 kt or 

SFO Bridge Approach...Similar to SFO. 

Monterey Bay Terminals...LIFR cigs continuing overnight and into
Monday morning. Clearing expected around 16-18z with VFR after
18z. Light and variable winds overnight. 


.MARINE...As of 8:30 PM PDT Sunday...High pressure over the 
eastern Pacific will result in gusty northwesterly winds 
continuing over the northern outer waters and through the coastal 
gaps into Tuesday. Winds will diminish across the waters on 
Tuesday as high pressure over the Pacific weakens and low pressure
develops over the Pacific Northwest. Steep fresh swell will 
continue through Tuesday over the northern outer waters as a 
result of gusty winds.


     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm




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