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Area forecast discussion 
National Weather Service San Francisco Bay area
303 am PDT Friday Mar 27 2015

Synopsis...a return of coastal fog and light onshore flow will
mean cooler temperatures today...especially near the coast.
Onshore flow will weaken on Saturday... and result in mostly clear
skies and warming temperatures for Sunday. Cooler temperatures are
then expected beginning on Monday. Dry weather to persist through
the forecast period.

&&

Discussion...as of 3:03 am PDT Friday...a very shallow marine
layer right along the coast has resulted in some patchy dense fog
near the coast...around the Monterey Bay and into the northern Salinas
valley. Currently the visibilities at kmry...ksns and kwvi are
wavering between 1/2 and 1/4 mile...as well as Half Moon Bay. A
very shallow fog layer is also showing up behind the buildings in
San Francisco on webcams. Given the extreme shallow nature of this
fog...it is not expected to persist too long this
morning...although the onshore wind flow will increase as the
onshore surface pressure gradient tightens throughout the day. The
00z nam12 indicates that the sfo-SAC surface pressure gradient
will increase to 3.5 mb by 00z Saturday which would result in a
strong enough sea breeze to bring cooler air inland. As a
result...today's high temperatures are forecast to be from 5-15
degrees cooler than those on Thursday.

Saturday should see similar temperatures with 60s and 70s most
areas...and up to the middle 80s far inland areas. A weak ridge of
high pressure will then build over the West Coast on Sunday for
slight warming. By early next week...however...a trough is prognosticated
to brush across the West Coast including northern California.
This will bring cooler temperatures to the district by Tuesday and
Wednesday...with highs expected to be in the 60s and 70s. Rain
chances with this trough will remain well to the north. Zonal
flow aloft to maintain across the West Coast through the remainder
of the forecast period.

&&

Aviation...as of 9:45 PM PDT Thursday...fog has developed along
the coast this evening and will impact mry and sns. Warm and dry
airmass over the interior will keep fog and low ceilings out of the
sfo Bay area.

Vicinity of ksfo...VFR through Friday.

Sfo bridge approach...similar to ksfo.

Monterey Bay area terminals...IFR for ceilings and visibilities through 12z.
Drainage wind from the sns valley expected to push fog out after
12z.

&&

Marine...as of 2:45 am PDT Friday...the surface pressure
gradient will increase today as a storm system passes to the
north. This will result in increasing north westerly winds across
the coastal waters. The strengthening winds will generate steep
fresh swell which will persist through the weekend and possibly
into the first half of next week.

&&

Mtr watches/warnings/advisories...
... Arena to pt Reyes 10-60 nm from 2 PM
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm from 2 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm from 5 PM
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm from 5 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm from 5 PM
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm from 2 PM
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm from 5 PM
Small Craft Advisory...sf Bay north of the Bay Bridge from 2 PM
Small Craft Advisory...sf Bay south of the Bay Bridge from 2 PM

&&

$$

Public forecast: Sims
aviation: west pi
marine: Larry

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