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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 240956
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
256 AM PDT Mon Jun 24 2019

.SYNOPSIS...A cooling trend will get underway today 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 slightly
below seasonal averages. 

&&

.DISCUSSION...As of 2:55 AM PDT Monday...Low clouds and fog 
formed overnight along most of our coastline from Bodega Bay 
southward, and also locally inland through the Golden Gate and up 
the Salinas Valley. This increasing coverage of marine layer 
stratus and fog is in response to a gradual uptick in onshore flow
as the upper ridge that brought very warm temperatures to our 
inland areas over the weekend begins to break down. The marine 
layer is still relatively shallow at present, but is expected to 
deepen over the next few days as an upper trough currently 
settling over the Pacific Northwest digs south over California. 
The deepening trough will also enhance onshore flow and bring a 
cooler airmass south into California. 850 mb temperatures are 
forecast to drop from about 21 deg C presently to around 11 deg C 
by Wednesday. Thus, we can expect a robust cooling trend through 
midweek. By Wednesday, high temperatures are forecast to be as 
much as 20 degrees cooler than this past weekend's temps and be 
anywhere from 5 to 12 degrees cooler than normal.

The models are in good agreement regarding this upcoming cooling
trend and indicate that Wednesday and Thursday will be the coolest
days of the week. Slightly warmer temperatures are expected on
Friday and on into the weekend, as the core of the upper trough
lifts to the northeast. However, the longwave trough position will
remain positioned near the West Coast, and so temperatures will
likely remain at least slightly below average on through the
upcoming weekend. 

In the longer range, the ensemble mean of both the GFS and ECMWF
indicate that the longwave trough position will retrograde as we
move into early July, allowing a ridge over the Desert Southwest
to build back towards California. Thus, we may see warmer
temperatures by the July 4th holiday, especially across inland
areas.  

&&

.AVIATION...as 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 
sites. 

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 
less.

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 2:06 AM PDT Monday...Gusty northwesterly winds 
will persist over the northern outer waters and along the coast 
north of Point Reyes into Tuesday as high pressure remains over 
the eastern Pacific. These winds will result in steep fresh swell 
creating hazardous conditions over the waters, especially for 
smaller vessels. Winds will diminish on Tuesday as high pressure 
weakens and an upper low moves offshore of the Pacific Northwest.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: ST
MARINE: AS

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