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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 191759

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1059 AM PDT Wed Jun 19 2019

.SYNOPSIS...Cooler temperatures are expected today and Thursday
before trending warmer Friday and Saturday. There is the potential
for moderately gusty offshore winds over the North and East Bay 
hills Thursday and Friday nights. 

&& of 9:05 AM PDT Wednesday...The marine layer is 
about 1500 feet deep and current satellite imagery shows coastal 
low clouds extending well inland this morning. Stratus should be 
fairly slow to clear from near-coastal areas as the area remains 
under a moderate onshore flow, with 2.1 mb from SFO to SAC. High 
temperatures today are forecast to be a few degrees cooler than 
yesterday in most places, with 60s to lower 70s at the coast, and 
80s to lower 90s inland. Some of the warmest inland areas could 
see highs in the middle 90s. 

The upper level ridge off the California coast will continue to 
weaken as an upper level low drops south from Western Canada into
the Pacific Northwest. This will lead to continued cooling during 
the next couple of days. Thursday will be the coolest day as an 
upper level disturbance moves south across Nevada with the trough 
axis moving through our district. This disturbance will tighten 
an offshore surface pressure gradient with north to northeast 
winds increasing Thursday night as this trough moves through. The 
12Z run of the NAM12 model shows 925 mb winds in the 25 to 35 kt 
range...strongest winds over the higher terrain in Napa County. 
After weakening on Friday the north to northeast winds will ramp 
up once again Friday night as the flow aloft becomes northeast on 
the back side of the trough bringing another night of potentially 
gusty winds for the North and East Bay hills Friday night. 
Currently there are no watches or advisories for the North and 
East Bay hills but will continue to monitor. 

Longer range models indicate a long-wave upper trough over the
eastern Pacific, with high pressure over the Rocky Mountain 
states. This will maintain cool or near seasonally normal temps 
going into the first week of Summer. 

&& of 11:00 AM PDT Wednesday...For 18z TAFs. Marine
layer deepened to around 2000 feet this morning as the shortwave
ridge weakened and onshore flow increased. Winds near the coast
have been southerly with anticyclonic rotation associated with
coastal eddies over the Monterey and San Francisco Bay feeding
stratus into the bays a little longer than expected. Low clouds 
were widespread this morning and are retreating from inland areas.
Stratus is expected to remain along the coast this afternoon with
VFR at the TAF sites. Winds will become onshore and increase this
afternoon, with most sites experiencing speeds of 10-15 kt. For 
tonight, onshore flow is expected to persist and a return to MVFR 
or lower cigs are expected at all terminals by sunrise.

Vicinity of KSFO...Clouds are rapidly decreasing per satellite and
web cams with full clearing expected to occur around or shortly
after 18z. Winds this afternoon will become onshore and increase 
with speeds of around 15 kt, and occasional gusts to around 20 kt.
Borderline MVFR/IFR cigs will develop overnight tonight and
continue through Thursday morning.

SFO Bridge Approach...A slightly thicker area of stratus over SF
Bay will result in clearing occurring closer to 19z over parts of
the approach. Otherwise, similar to SFO.  

Monterey Bay Terminals...MVFR cigs will continue through 19-20z
with clearing expected for the rest of the afternoon. Winds
becoming onshore with speeds around 10-15 kt. IFR expected to
develop early to mid evening with LIFR possible at MRY after
midnight continuing through Thursday morning. 

&& of 8:37 AM PDT Wednesday...Generally light to 
locally moderate south to southwesterly winds will prevail across 
the coastal waters with the exception of strengthening northerly 
winds over the northernmost outer waters. Strong northerly Gale 
Force winds are forecast to be confined mainly to the northernmost
outer waters north of Point Reyes from this evening through at 
least Thursday evening. Gusty northerly winds will become more 
widespread across the coastal waters Thursday evening through 
Friday. This will result in steep fresh swell creating hazardous 
seas conditions, particularly for smaller vessels.


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm




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