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Area forecast discussion 
National Weather Service San Francisco Bay area
444 am PDT sun may 3 2015

Synopsis...a relatively deep marine layer and persistent onshore
flow will maintain areas of night and morning low clouds through
the middle of the week...along with temperatures near to slightly
below normal. An upper level low is then forecast to develop over
California by Thursday. This low will mix out the marine
layer...but also maintain relatively cool weather conditions into
the second half of the week. There is also a slight chance of
showers with this weather system...mainly across the southern
portion of our area from late Thursday night through Friday.

&&

Discussion...as of 3:10 am PDT Sunday...the marine layer has
deepened slightly since early yesterday morning and is currently
at a depth of just over 2000 feet at Fort Ord. Onshore pressure
gradients are similar to 24 hours ago...although the Delta breeze
at Travis AFB is stronger early this morning with the 2 am
observation indicating onshore winds of 25g33 knots. Widespread
low clouds have developed in coastal areas and also into many
valleys. Clearing will likely occur a little later today given the
increased depth of the marine layer. All of these factors suggest
that the cooling trend that began on Friday will continue
today...although the magnitude of today's cooling is expected to
be less than what occurred during the past two days.

A weak upper trough currently off the West Coast is forecast to
shift eastward over the California coast by Monday morning. Both the NAM
and WRF models indicate this will result in an even greater inland
surge of marine layer clouds tonight...as well as continued cool
conditions into Monday.

After the weak upper trough moves inland on Monday...surface high
pressure will strengthen off the northern California coast...resulting in
increasing northwest winds along the coast on Monday night and
Tuesday. These winds should produce sufficient mixing to clear out
much of the low cloudiness by Tuesday afternoon and thus bring
about slight warming on Tuesday.

An upper low is forecast to develop over the Pacific northwest by midweek.
The GFS and European model (ecmwf) agree reasonably well in dropping that low due
south across northern and central California from late Wednesday
night through Thursday night...and then ejecting that low
eastward on Friday. Both models also forecast scattered light
precipitation across portions of our area from Thursday afternoon
through late Friday...with the most widespread shower activity
projected to occur across the southern part of our area late
Thursday night and Friday morning as shortwave rotates inland over
the central coast.

The airmass over our area will cool several degrees from late
Wednesday into Thursday as the upper low drops in from the north.
This cooling will be sufficient to mix out the marine layer across
the northern part of our area by late Wednesday and in all areas
by Thursday. Temperatures will cool below normal in all areas by
Thursday and remain cool through the end of the week.

The upper low is forecast to move well off to our east by late
Friday...and shortwave ridging is expected to produce dry and
slightly warmer weather next weekend. But the longer range models
maintain an unsettled pattern...with another weak weather system
projected to approach California early next week.

&&

Aviation...as of 4:36 am PDT Sunday...as noted above deep marine
layer in place with widespread MVFR ceilings with a few pockets of IFR
conditions. Ksjc and klvk are on the edge and latest trends
suggest stratus around sunrise. Based on latest guidance clearing
will be middle morning for many locations with VFR this afternoon.
Ceilings return again tonight. Conf is medium-high.

Vicinity of ksfo...MVFR ceilings with clearing 17-18z. Brief period of
NE winds possible. Stronger west push of winds this afternoon.

Sfo bridge approach...similar to sfo.

Monterey Bay area terminals...MVFR ceilings through 18z. VFR this afternoon.

&&

Beaches...as of 4:36 am PDT Sunday...no real change from previous
forecast. A series of long period southerly swells will impact the
central coast today. Pt Conception buoy is already showing 3.5 feet
at 25 seconds. Although the wave heights associated with these
long period waves will be relatively small...4 to 6 feet...the
powerful nature of long period waves will result in exceptionally
strong rip currents along the coast especially on southerly facing
beaches such as Stinson Beach in Marin County and the beaches
along the Monterey Bay coast of Santa Cruz County.
Additionally...these long period waves will also result in large
shore break at Twin Lakes state beach and the Santa Cruz boardwalk
beach. Large shore break can result in neck and back injuries. If
you plan on entering the water please do so near a lifeguard and
always keep an eye on the ocean when visiting the beach.

&&

Marine...as of 04:31 am PDT Sunday...gusty northerly winds will
continue over the northern outer waters through early next week.
Elsewhere...southerly flow will continue today. Northerly flow
will develop over most of the coastal waters tonight and Monday as
high pressure builds over the region. A long period southerly
swell will impact the coastal waters Sunday and continue through
Tuesday.

&&

Mtr watches/warnings/advisories...
... Arena to pt Reyes 10-60 nm
Small Craft Advisory...sf Bay north of the Bay Bridge from 3 PM

&&

$$

Public forecast: dykema
aviation/marine: mm

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