Small Craft Advisory 74, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
140 PM PDT Wed May 9 2018

.SYNOPSIS...Seasonable temperatures today into Thursday followed
by a warming trend into Friday. Some strong northeast winds
develop in the North Bay Mountains, East Bay Hills and Santa Cruz
Mountains Friday night, but mostly end by sunrise Saturday.
Continued seasonably mild Saturday but then cooling into Sunday as
an upper low impacts the region.

&&

.DISCUSSION...as of 01:40 PM PDT Wednesday...Morning low clouds
and patchy fog dissipated giving way to abundant sunshine across
the Bay Area this afternoon. Onshore flow is keeping the immediate
coast and bay shoreline in check, but interior locations are
running a few warmer than 24 hours ago for the most part. The
North Bay for instance is approaching 80 degrees as of 1 PM.

Not much has changed in the short term forecast. Latest hi-res
models continue to develop another round of low clouds/fog along
the coast and inland tonight. Patchy drizzle will be possible as
well as models generate very light QPF along the coast. Clouds
will once again peel back to the coast mid-late morning Thursday
with sunny skies in the afternoon. Similar to today, temperatures
creep a few degrees, especially across the interior. Highs will be
in the 60s/low 70s coast and 70s/mid 80s inland.

By Friday morning the longwave pattern shows an upper low swinging
into the Great Basin resulting in offshore flow. Morning low
clouds and fog will be possible again, but with less coverage
given the developing NE winds. Clouds will be most likely along
the San Mateo Coast southward to Big Sur. Expect earlier burn off
time given the NE/downslope flow. Offshore flow will also lead to
warmer temperatures on Friday. It should noted that the overall
model trend has been to back off on heat potential for Friday.
None the less, temperatures will still be mild with many inland
locations in the 80s.

Offshore flow really ramps up as the upper low drifts westward
tightening the pressure gradient over the Bay Area Friday night.
All models convey the strong winds at 925 mb (~2,500 ft) with
30-45 kt wind barbs. High wind watch remains in effect Friday
evening through Saturday morning. Decided to include the Santa
Cruz Mountains as well. Winds will be strongest over the terrain
of Napa with gusts to 60 mph, but gusts 45-55 mph seem likely for
the East Bay Hills and Santa Cruz Mountains. Of concern would be
any remaining fire weakened trees across the North Bay could come
down with the stronger wind.

Saturday will be a tricky forecast as the local WRF model is
suggesting a southerly surge coming up the coast. If the surge
happens temps will be much cooler at the immediate coast. Inland
areas of the North and East Bay will still be rather mild given
the lingering, but weakening offshore flow.

Cool and dry weather for late in the weekend into next week as the
upper low continues to drift westward.

&&

.AVIATION...As of 10:44 AM PDT Wednesday...For 18z Tafs. Patchy
stratus remains across the Bay Area, affecting mainly Bay Area
terminals as of 1730z. Expect clearing by 18-19z for all TAF
sites. Have stratus returning relatively early tonight at all
sites, between 03-05z for Bay Area terminals and as early as 02z
for Monterey Bay terminals. Westerly winds will be on the breezy
side through the day, occasionally gusty at many sites. KSFO is
already seeing sustained west winds around 15 kt. Breezy winds
will continue through the evening and possibly spilling into the
overnight hours as an upper level trough axis pushes onshore.

Vicinity of KSFO...VFR forecast by 1830z and prevailing through
the afternoon. MVFR cigs returning around 04-05z, possibly as
early as 03z. Breezy west winds through the day, around 20 kt,
gusting to near 30 kt after 20Z.

SFO Bridge Approach...Expect clearing over the bridge by 19z,
perhaps a half hour earlier. Otherwise, similar to KSFO.

Monterey Bay Terminals...Slow clearing of stratus occuring at
KMRY. Cigs have finally lifted to IFR levels. Expect VFR by 18z
at KSNS and by 1830z at KMRY. Breezy onshore winds today and into
this evening, 10-15 kt with gusts around 20 kt in the afternoon.

&&

.MARINE...as of 8:57 AM PDT Wednesday...Northwest winds will
increase today as high pressure strengthens over the eastern
Pacific. Gale force winds are possible along the coast south of
Point Pinos this afternoon and evening. Winds will increase
further to gale force or near gale force Thursday and Friday,
especially over the northern waters as low pressure deepens over
the Great Basin.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Mry Bay until 9 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...SF Bay until 11 PM

&&

PUBLIC FORECAST: MM
AVIATION: BAM
MARINE: BAM/W Pi

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