Small Craft Advisory 93, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
257 AM PDT Mon May 28 2018

.SYNOPSIS...A warming trend will continue today as high pressure
builds over California and onshore flow weakens. Coastal cooling
will develop on Tuesday with more widespread and significant
cooling expected by Wednesday as a dry upper trough develops over
the state. Cool conditions will persist into Thursday, with modest
warming expected Friday into Saturday.

&&

.DISCUSSION...As of 2:55 AM PDT Monday...Latest Fort Ord Profiler
indicates the depth of the marine layer has decreased to about
500 feet as an upper ridge continues to strengthen over
California. Current satellite imagery shows areas of low
clouds/fog along the coast from the Golden Gate southward. Given
the shallow nature of the marine layer...and relatively weak
onshore pressure gradients...expect low clouds and fog to mostly
remain confined to the immediate coast this morning. Latest WRF
shows drying in the boundary layer through the morning hours,
suggesting clearing in most coastal areas by late morning,
although a few patches of coastal fog may linger through the day.
The warming trend that got underway on Sunday will continue today
as the airmass over our region continues to warm under the upper
ridge. High temperatures today are forecast to be about 5 to 10
degrees warmer than yesterday. The warmest inland valleys are
expected to warm into the low to mid 90s while the coastal valleys
and areas near San Francisco Bay are forecast to see afternoon
highs in the 80s. Light onshore flow will keep areas near the
ocean relatively cool by comparison...mostly in the upper 60s and
70s.

Today is expected to be the warmest day of the week for most of
our forecast area. A dry upper trough approaching from the
northwest on Tuesday will trigger an increase in onshore flow,
resulting in cooling at the coast and in the coastal valleys. The
marine layer will still probably be relatively shallow on Tuesday
and so the inland valleys and hills are expected to remain warm
for one more more day. The upper trough is then forecast to dig
south along the California coast by midweek, resulting in
widespread and significant cooling on Wednesday. High
temperatures on Wednesday are forecast to be about 10 degrees
cooler than today in coastal areas and from 15 to 20 degrees
cooler inland. Night and morning low clouds and fog are expected
to increase along the coast by Tuesday and then spread into the
valleys on Wednesday and Thursday.

The models agree that the trough will move off to our east late in
the week, allowing for a modest warmup on Friday. As we move into
next weekend the models disagree somewhat. The GFS shows the next
trough approaching the northern California coast on Saturday,
resulting in renewed cooling that day. The ECMWF shows that trough
coming in about 24 hours later and thus delays any weekend
cooling until Sunday.

&&

.PREV DISCUSSION...as of 1:35 PM PDT Sunday...Two parts of
today's forecast verified well: much warmer and less cloud cover.
The forecast did come up a little short regarding the amount of
clearing along the immediate coast. Afternoon visible satellite
still shows pesky low clouds hugging the immediate coast from near
the Golden Gate southward to Big Sur. There is a slow trend for
some additional clearing along the coast, but it looks like some
clouds may linger through the afternoon. None the less, interior
locations warmed up nicely today with temps in the 70s to lower
80s, which is about 15-20 degrees warmer than 24 hours ago.

No major changes to the overall forecast. High pressure will
continue to build across NorCal through Monday night. The warming
noticed today across the interior will warm a few more tomorrow.
In fact, some interior spots will dip into the lower 90s. Likely
some of the warmest temps observed in a few weeks. Max temps in
the 80s and 90s tomorrow would be 5-10 degrees above normal for
late May. Individuals with outdoor activities should be mindful of
the warmer temperatures and plan accordingly - stay hydrated,
wear sunscreen, take breaks, etc. Simply put, tomorrow could be a
shock for some as it will feel noticeably warmer across the
interior. At the coast is a different story as onshore flow
lingers. Similar to today, pesky low clouds will keep the
immediate coast in check with seasonable temps.

By Tuesday the ridge of high pressure moves eastward as a trough
of low pressure begins to deepen off the West Coast. Stronger
onshore flow returns reinvigorating the extent of night/morning
clouds. Max temps will begin the downward trend on Tuesday.

By Wednesday/Thursday the upper trough is forecast to be over the
Bay Area with some of the coldest weather of the upcoming week. By
Thursday max temps will struggle to even hit 70 across the
interior, which is about 5-10 degrees below normal. What a change
from Monday to Thursday.

A slight warming trending will develop Friday into next weekend as
high pressure returns with warming 850mb temps.

&&

.AVIATION...As of 10:43 PM PDT Sunday...For 06z TAFs. Dry
northerly flow over the region will maintain mostly clear skies
across area terminals through the forecast period. Otherwise light
winds will prevail tonight. Winds will strengthen Monday
afternoon with the onset of the seabreeze.

High confidence.

Vicinity of KSFO...VFR conditions will prevail through the
forecast period. West winds will ease overnight then increase
once again Monday afternoon to around 15 to 20 kt.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions will prevail through
tonight. Light winds.

&&

.MARINE...as of 9:00 PM PDT Sunday...Moderate to strong northwest
winds will continue through this evening and into the upcoming
week, especially over the northern outer waters. Steep fresh swell
will be generated by the moderate to locally strong winds. The
pressure gradient is forecast to gradually tighten along the
northern California coast starting Monday afternoon. This will
increase NW winds to gale force or near gale force by Tuesday for
the outer waters through at least Wednesday, before decreasing.
Very rough and erratic seas can be expected with these winds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 PM

&&

PUBLIC FORECAST: Dykema
AVIATION: CW
MARINE: BAM/CW

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