Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
451 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 4:51 am PDT Friday...the current satellite infrared
fog product is showing mostly clear skies around the forecast area
this morning with the exception of low clouds and fog along the
immediate coast...impacting ksns and kmry. A large field of
stratus also is present over ocean along the California coast at
A low pressure system is pushing towards the Pacific northwest
which will drag a cold front into northern California this
morning. This cold front may push stratus into the terminals by
late afternoon early evening. In addition to this front the local
pressure gradient is expected to increase...promoting moderate
gusty winds later this morning into the afternoon and evening
Vicinity of ksfo...VFR is expected to prevail today with stratus
possible this evening. Gusty west winds will reach 15 to 20 knots
this afternoon with gusts to 25 knots.
Confidence is high.
Sfo bridge approach...similar to ksfo.
Monterey Bay area terminals...ground fog will reduce visible to around
1/4sm this morning but is expected to burn off by around 1600z.
However...once the fog Burns off sct007-012 will linger around
through this afternoon. And early return of bkn008 is likely by
0200z. Winds are expected to increase out of the west today
reaching 10 to 15 knots this afternoon with gusts to 20 knots possible.
Confidence is moderate.
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.
... 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
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