National Weather Service Raw Text Product

Displaying AFOS PIL: AFDMTR Received: 2018-01-12 17:55 UTC

FXUS66 KMTR 121755

Area Forecast Discussion
National Weather Service San Francisco Bay Area
955 AM PST Fri Jan 12 2018

.SYNOPSIS...High pressure will build over California today and 
bring dry and mild weather to the area through the Martin Luther 
King Jr. Holiday Weekend. The next chance of rain will be on 
Monday night and Tuesday, with additional rain chances next 
Thursday and Friday.


.DISCUSSION...As of 8:20 AM PST Friday...Patchy fog continues
around our region this morning with many spots under two miles.
Worst conditions appear to be over the East Bay Interior valleys
with less than 1/2 mile in many spots. Upper air sounding nicely
showed the surface inversion which gave favorable conditions today
for fog development. Conditions will improve later this morning
with upper 50s to the mid 60s forecast. 

Latest models in are fairly close to the previous couple of runs.
Look for rainfall to return on Tuesday with a second round slated
for Thursday.

.PREVIOUS DISCUSSION....Satellite fog product is showing low 
clouds over a portion of the coastal waters, and also spreading 
through most inland valleys at this time. There is also a fair 
amount of fog being reported at area airports with visibilities 
bouncing around from 1/4 mile to 7 miles at our TAF sites. A dense
fog advisory may be needed towards dawn if 1/4 mile or less 
becomes more widespread. Otherwise, today should see warmer high 
temperatures with most locations seeing highs in the 60s. Even 
warmer temperatures are anticipated for Saturday and Sunday as 
high pressure aloft builds over the state, and warmest inland 
areas could see highs in the mid 70s.

The next rain event is forecast to begin late Monday as an upper
level trough approaches the coast. Light rain is expected to begin
across much of the San Francisco Bay Area by late Monday night 
and early Tuesday, and then reaching the Monterey Bay area Tuesday
morning. The heaviest rainfall is expected to be mostly north of 
our CWA but northern Sonoma and Napa counties could see periods of
moderate rainfall at times. This system is expected to be through
our area by midday Tuesday with perhaps some lingering early 
afternoon showers. Rainfall totals with the Monday Night/Tuesday 
system are currently forecast to range from 0.25-0.75" in the 
North Bay...locally up to 1.25" in the far northern coastal 
mountains...and generally a third of an inch of less south of the 
Golden Gate.

A second system is forecast to impact the district with 
widespread rain on Thursday with showers continuing into Friday. 
This second system is currently expected to be about as wet as the
first (or somewhat wetter for areas from San Francisco 
southward). Medium range models still indicate another system 
after next weekend. 

&& of 10:00 AM PST Friday...For 18z tafs. Latest
GOESR CH2 imagery over the area shows abundant fog throughout the
Central Valley and smaller valleys of the San Francisco and 
Monterey Bay areas. Despite northeast winds that would normally
advect in drier air and hasten the morning burn off, the abundant
low level moisture over the Central Valley is doing the opposite
and delaying the morning burn off. Expect to see patchy dense fog
in the eastern Carquinez Strait/Delta into the afternoon and
possibly over areas like KAPC KLVK and KCCR. Elsewhere, seeing
some contraction on the west most boundary of the low level 
moisture near KSJC and on the northern flank near KSTS, so 
looking more optimistic for VFR there by late morning. Elsewhere, 
KOAK and KSFO will be the main tossups, with current thinking
around 21Z. Monterey Bay should remain clear, with KSNS possibly
lingering as low level moisture rotating around the southern San
Joaquin Valley is advected in from the southeast.

Vicinity of KSFO...Low confidence, current thinking around
2030-2130 for improvements. The key will be to watch the western
flank for continued eastward progression, which is making slow but
steady progress. Light northeast winds become light northwest 
later in the day.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...SKC at KMRY. Low clouds over the Salinas
Valley are slowly burning off from north to south, but are being
reinforced from south to north. Since KSNS is on the extreme north
side of the valley, expect to see it clear out by late morning to
around lunch time, with continued low clouds from Gonzales

&& of 09:46 AM PST Friday...Light north winds across
most of the waters today, except from Point Pinos southward, where
stronger north winds will prevail. A long period northwest swell
will continue to pass through the waters today. A longer period
northwest swell will arrive late Sunday into early Monday.


     .Tday...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm




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