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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 201151

Area Forecast Discussion
National Weather Service San Francisco Bay Area
451 AM PDT Sat Oct 20 2018

.SYNOPSIS...Continued mostly sunny and seasonably warm through 
the weekend. Some cooling back to more seasonable temperatures by 
early next with onshore flow and a deeper marine layer. High 
pressure stays in place through next week with continued dry 


.DISCUSSION...as of 3:11 AM PDT Saturday...Marine layer is only a
couple hundred feet along the coast with fog and low clouds over 
the ocean. Locally some dense fog is forming in places like Santa 
Rosa and Monterey reporting 1/4 mile fog. The onshore sfo-sac is 
only 0.5 mb and with the shallow marine layer dont expect much 
inland intrusion of stratus this morning. Large scale gradients 
still feature 8 mb of offshore from the Nevada deserts to the 
coast. This all points to another sunny and warm day with lots of 
highs in the 80s inland with 70s around the coast/bays.

A very weak 500 mb low will move up the coast today but there
doesnt appear to be much surface reflection or for that matter
much of an impact on the marine layer. The main impact will be
some subtle airmass cooling at 850 mb by Sunday with some precip
developing over the southern Sierra. So for the Bay Area we expect
2-4 degrees of cooling on average for Sunday afternoon but still
ideal weather for the second half of the weekend.

More noted cooling by Monday with highs generally in the 70s
inland and 60s coast as 850 mb temps drop to 12-14 Celsius.

Mid to long range forecast for next week then shows the pattern
becoming more active across Oregon into far Northern California
but not expecting much impact for the Bay Area other than perhaps
some North Bay high clouds as jet energy passes just to our north.
Meanwhile high pressure over Southern California will nose
northward with warm and dry weather pushing into the Central
Coast. Continued dry through next work week with the next front 
poised perhaps by the weekend of Oct 28th.


.AVIATION...as of 4:50 AM PDT Saturday...For 12z tafs. Shallow
marine layer bringing cloud bases to 500 foot or less, with areas
of thin patchy fog near the coast. Look for a few fingers of thin
stratus sneaking through the Golden Gate gap and along the lip of
the Monterey Bay through sunrise and potentially into mid morning
before mixing out. Generally VFR regionwise, except brief FEW-
SCT002-004 at Bay Area terminals and a thin fog bank over
KSTS/KMRY.  Winds light. 

Vicinity of KSFO...VFR. Patchy FEW003-SCT003 possible thru 
sunrise hours. Light winds.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR except patchy dense fog near the
southern lip of the Monterey Bay incl KMRY thru sunrise hours.
Light winds.  


.MARINE...as of 02:45 AM PDT Saturday...Generally light to locally
breezy northwesterly winds will continue as high pressure over the
Great Basin and the eastern  Pacific weakens heading into next
week. Mixed moderate period  northwest and southerly swell will
persist before a longer period  southerly swell arrives early next





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