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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 172344

Area Forecast Discussion
National Weather Service San Francisco Bay Area
444 PM PDT Fri May 17 2019

.SYNOPSIS...The next front will quickly approach on Saturday with
morning rain in the North Bay spreading southward through the day
before turning to showers Saturday evening. Numerous showers will
linger on Sunday as the core of the upper low passes over the 
region. Dry weather returns Monday but yet another system will 
bring a chance of rain Monday night into Tuesday.

&& of 1:32 PM PDT Friday...Under mostly sunny to 
partly cloudy skies, afternoon temperatures are warming above 
yesterday's temperatures at this time by several degrees with 
current temperatures in the upper 50s to upper 60s. 

Meanwhile, an upper level trough continues to approach the coast.
This trough will bring a front that will spread rain from north 
to south across the area on Saturday. Models remain in good 
agreement showing a well defined cold front moving from north to 
south through the day Saturday across the Bay Area. Rain will 
develop along the Sonoma county coast by 8 am Saturday, then 
spreading through the North Bay by late Saturday morning. The 
proximity of the upper low, jet dynamics and well defined surface 
cold front all suggest that most areas will see a several hour 
period of steady rainfall from late morning through mid afternoon,
likely impacting Saturday outdoor activities. Precip should turn 
to showers by early evening as the surface front moves to the east.

The core of the cold upper low will pass across northern
California Saturday night into Sunday maintaining showers across
the region with isolated thunderstorms being possible as well on 
Sunday. Showers will end Sunday night with dry but cool weather on
Monday. Another cold shortwave is forecast to drop southward 
along the coast from British Columbia Monday night with continued 
shower chances into Tuesday. 

Long range models keep the trough over the west coast for much of
next week keeping below normal temperatures across the Bay Area. 
Latest climate outlooks keep cool and wetter than normal 
conditions across California until nearly the end of May. 

&& of 4:43 PM PDT Friday...Drier air aloft descending
towards the lower levels has caused clearing of the stratus this 
afternoon. VFR conditions should hold until Saturday morning when 
the next frontal system approaches the area. Models showing deep 
moisture arriving between 16-18Z in the SFO Bay Area and 18-20Z in
the MRY Bay Area which is when rain is expected to begin with 
cigs lowering to near 3000 feet. Winds will become southerly 
overnight with max speeds reaching 15 kt gusting to 20-23 kt late 
Saturday morning. 

Vicinity of KSFO...VFR expected tonight. West winds gusting to 20
kt through 04Z. Clouds with cigs down to 4000 ft Saturday 
morning may produce some light rain. Steady light rain is expected
Saturday afternoon. Winds becoming southeast and increasing to 15
kt midday.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR expected through tonight. Cigs with
heights at or above 4000 feet expected late tonight after
06Z. Winds switching to light southeast Saturday morning
increasing Saturday afternoon with gusts to 20 kt in the Salinas 

&& of 04:24 PM PDT Friday...Light to moderate winds will
continue with locally gusty winds  along the Big Sur coast and
around the Monterey Bay into this evening. Winds will increase and
turn southerly tonight ahead of an approaching system. These winds
will generate steep fresh swell creating hazardous conditions over
the waters, particularly for smaller vessels. Winds will turn more
westerly towards the end of the weekend.


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




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