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Area forecast discussion 
National Weather Service San Francisco Bay area
1052 PM PDT Friday Oct 24 2014

Synopsis...a cold front will approach the coast late on Friday
night. Southerly winds will increase ahead of the front and become
locally strong and gusty near the coast and in the hills late
Friday night and Saturday morning. At the same time...rain will
spread across much of the region. The front will pass through
quickly on Saturday morning...but cooler unstable air will bring
scattered showers to much of the area Saturday afternoon and
evening. A few thunderstorms may develop as well...especially from
the Santa Cruz Mountains northward. Drier and cooler weather is
expected Sunday with a warming trend beginning Monday as high
pressure rebuilds along the coast.

&&

Discussion...as of 8:55 PM PDT Friday...a storm system over the
eastern Pacific continues to advance towards the West Coast at a
moderate pace. Satellite shows a well-defined cold front moving
just inside 130w and a pool of cold unstable air behind the front.

Southerly winds have already developed ahead of the front and have
begun to increase over our coastal waters. Wind speeds will
gradually ramp up overnight as the front draws closer. Winds will
become locally strong and gusty near the ocean and in the hills by
late tonight. Based on the latest NAM...the cold front should pass
through the North Bay by about sunrise Saturday morning and then
through the rest of the sf Bay area by middle morning. Winds are
forecast to veer more to the southwest after frontal passage...but
remain quite strong and gusty through midday Saturday. This looks
like a marginal Wind Advisory situation...with the most
significant pressure gradients and winds forecast to remain to our
north. Wind gusts up in the 40-50 miles per hour range will probably only
occur in some of our windiest coastal and Ridgetop locations late
tonight and Saturday morning. However...drought-stressed trees
have not been subjected to winds of any significance for quite
some time and many are prone to toppling with this first blustery
storm system of the season. Power outages or property damage are
possible due to fallen trees or tree limbs. Therefore...will
continue with a Wind Advisory for the North Bay coast and
mountains...the San Mateo and Santa Cruz County coasts...and the
Santa Cruz Mountains from 3 am to noon PDT on Saturday.

The cold front will spread rain across most of our region late
tonight and Saturday morning. There may be a bit of a break in the
precipitation action late Saturday morning after frontal passage...but
then bands of showers are expected to rotate through our region as
the cold and unstable airmass associated with the upper trough
arrives. The 00z NAM has backed off on the amount of instability
forecast across the sf Bay area on Saturday afternoon and so
thunderstorm chances appear to be dwindling. However...as pointed
out in the previous discussion...continued much warmer than normal
sea surface temperatures along our coast may provide the necessary
ingredient for greater instability and isolated thunderstorms.

Showers are expected to taper of Saturday evening and end by
daybreak Sunday. Sunday will be a relatively cool day with
northwest breezes under partly cloudy skies.

A warming trend is forecast for the first half of the work week as
a low amplitude upper ridge builds over California. The pattern will
remain active over the northeast Pacific...with storm systems
forecast to ride over the ridge and into the Pacific northwest. It currently
appears very unlikely that any of this precipitation will make it into
our area...and we may want to consider removing probability of precipitation from the
North Bay around the middle of next week.

Confidence in the forecast falls off considerably late in the
extended. The medium range models agree that the upper ridge will
move east by the end of next week...allowing the trough offshore to
approach the West Coast. But the forecast of precipitation onset in our area
varies considerably...from as early as Thursday night (gem) to as
late as Sunday night (ecmwf).

&&

Aviation...as of 10:51 PM PDT Friday...for 06z tafs. An
approaching low pressure system and associated cold front
situated off the northern California coast will bring increasing
southeasterly winds overnight and wet runways by morning. T-storms
remain a concert for Saturday afternoon.

Vicinity of ksfo...VFR conditions expected through late tonight. Light
south winds will turn southeasterly and strengthen overnight. -Ra
expected around 11z tonight. By Saturday morning moderate and
gusty southeast winds and wet runways will impact the morning
traffic. Winds expected to veer southwesterly Saturday afternoon.

Ksfo bridge approach...similar to ksfo.

Monterey Bay area terminals...VFR conditions expected through
late tonight. Light winds will turn southeasterly overnight.
-Shra expected to develop around 12z-15z Saturday. By Saturday
morning southeast winds and wet runways will impact area
terminals. Winds expected to veer southwesterly Saturday
afternoon.

&&

Marine...as of 8:57 PM PDT Friday...low pressure situated west
of Cape Mendocino will continue to deepen tonight resulting in
strong southerly winds across the coastal waters. Gale force winds
will develop overnight across the northern waters with strong
small craft winds developing elsewhere. A line of rain and showers
will move through the waters early Saturday morning with
thunderstorms possible north of the Golden Gate Saturday
afternoon. Winds will ease and showers will end by Saturday night
with lighter winds and moderate seas Sunday into Monday.

&&

Mtr watches/warnings/advisories...
... Advisory...North Bay coast and mountains
Wind Advisory...San Mateo and Santa Cruz County coasts
Wind Advisory...Santa Cruz Mountains
Small Craft Advisory...sf Bay north of the Bay Bridge from 3 am
Small Craft Advisory...sf Bay south of the Bay Bridge from 3 am
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm from 3 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm from 3 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm from 3 am
glw...pt Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm until midnight
glw...pt Reyes to Pigeon pt 10-60 nm from midnight
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm from 9 PM
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm from 9 PM
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm until 1 am
glw...pt Arena to pt Reyes 0-10 nm from 1 am
Small Craft Advisory...rough bar advisory for sf bar from 5 am

&&

$$

Public forecast: dykema
aviation/marine: CW

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