Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 271146

Area Forecast Discussion
National Weather Service San Francisco Bay Area
446 AM PDT Sun May 27 2018

.SYNOPSIS...A robust warming trend is forecast through Memorial
Day as high pressure builds over California and onshore flow
weakens. Coastal cooling will develop by Tuesday with more
widespread and significant cooling expected by Wednesday as a dry
upper trough develops over the state.


.DISCUSSION...As of 2:40 AM PDT Sunday...Early morning satellite
imagery shows areas of low clouds, mainly in coastal areas south
of the Golden Gate, and also inland from Monterey Bay. Expect
low clouds to mostly clear by midday...although patchy clouds may
persist into the afternoon hours near the San Mateo County coast
and around the southern portion of Monterey Bay. Otherwise, mostly
sunny conditions are forecast for today as an upper ridge
currently centered offshore builds eastward along the California
coast. High temperatures today are forecast to climb to near
normal or slightly above, and be anywhere from 7 to 15 degrees
warmer than yesterday.

The upper ridge is forecast to continue strengthening over
California into Memorial Day, resulting in further airmass
warming and drying across our region. In addition, onshore flow is
forecast to decrease significantly by Monday morning. These
developments will result in an additional 10 degrees or so of
warming tomorrow. Monday`s highs are forecast to mostly be in the
70s near the ocean, and in the 80s to lower 90s inland. Coastal
low clouds on Monday morning will likely be limited to just a few
patches and most coastal areas should be sunny in the afternoon.

Monday will be the warmest day of the week for most of our area.
By Tuesday the models agree that the upper ridge axis will move
off to our east as a dry upper trough approaches from the
northwest. Onshore flow will begin to ramp up on Tuesday which
will result in cooling at the coast and in the coastal valleys.
The inland valleys and hills will probably remain mostly isolated
from the cool marine air on Tuesday and so those areas are
expected to remain warm one more day. However, by Wednesday the
upper trough is forecast to dig south along the California coast,
bringing much cooler air well inland. Temperatures by Wednesday
and Thursday are expected to drop to about 5 to 10 degrees below
normal. Also, look for an increase in night and morning low clouds
by Tuesday morning and especially by Wednesday morning. The upper
trough is forecast to begin to move off to our east by the end of
the week, allowing for at least a modest warming trend next


.AVIATION...As of 04:45 AM PDT Sunday...Drier air mass advecting
into Bay Area under northerly flow is scouring out the marine
layer for most areas leading to predominately VFR conditions.
Satellite imagery shows a thicker stratus deck alone the coast
from Half Moon Bay southward which is gradually being pushed
farther southward, mainly impacting KMRY/KSNS to some extant.
Satellite imagery also shows lower level moisture manifesting into
a BKN-OVC003 layer across the North Bay and increasingly across
the coast, which will lead to some LIFR conditions at KSTS.
KSFO/KOAK are in the low confidence zone between these two decks,
however, highest probability is VFR prevailing at those two
terminals with very brief sunrise surprise BKN010 deck forming
btwn 12-14Z this morning. Winds generally light today. Mostly
clear skies for tonight.

Vicinity of KSFO...VFR should prevail this morning however there
is a slight possibility that a SCT-BKN010 deck could develop
prior to or around sunrise this morning, hence the tempo in the
TAF. Otherwise, generally light winds north winds this morning
increasing to onshore breezy winds by the afternoon. VFR should
prevail tonight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Marine layer deteriorating this morning,
however, lingering stratus deck caught in the Monterey Bay eddy
could bring brief IFR cigs (BKN-OVC008) to the KMRY/KSNS/KWVI
terminals thru around 16Z this morning. Otherwise, light winds
today. Patchy cigs redevelop late tonight/early Monday.

&& of 04:39 AM PDT Sunday...Northwest winds will prevail
through the coming days with the strongest winds expected over the
outer waters north of Point Reyes. In addition to a northwest
swell, steep fresh swell will be generated by the moderate to
locally strong winds. Winds  increase in strength after the
Memorial Day weekend with possible  gale force winds over the
outer waters beginning Tuesday.


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 6 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 6 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 5 PM




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