Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1047 PM PST Sat Nov 22 2014
Synopsis...dry weather conditions and unseasonably mild
temperatures are expected through midweek as a ridge of high
pressure builds over the region.
Discussion...as of 8:50 PM PST Saturday...the weak front that moved
through our area earlier today has since moved well to our south
and all precipitation has ended. Because orographic enhancement
contributed significantly to rainfall intensity with this
system...rainfall totals varied considerably across the region.
Most lower elevation inland locations accumulated less than a
quarter of an inch. Some inland valleys locations in the North
Bay and lower elevation coastal locations picked up as much as a
half inch of rain. The coastal mountains fared much better with
several locations seeing more than an inch of rain...with isolated
spots in the Sonoma and Marin County coastal hills managing to
accumulate 2 to 3 inches from this system.
Surface high pressure is building across far northern California
this evening...and northerly winds have begun to develop in the
hills. North winds will likely increase overnight with local
gusts up to 30 miles per hour possible after midnight. These northerly winds
are forecast to continue well into Monday and will bring a much
drier airmass into our region. Patchy low clouds should mostly
clear overnight as this drier air begins to filters in.
However...the nocturnal inversion may trap enough moisture in the
valleys to result in patchy fog late tonight into early Sunday
morning. After a cool start on Sunday...temperatures will warm at
least a few degrees above normal under mostly sunny skies.
A low amplitude upper ridge centered offshore along 135w is
forecast to amplify over the next few days and shift eastward to
the West Coast by late Tuesday. The combination of light offshore
flow and a warming airmass under the strengthening upper ridge
will push daytime temperatures well above normal early in the work
week. High temperatures by Tuesday will range from the upper 60s to
middle 70s and be about 10 degrees above normal in most areas.
However...long late autumn nights...clear skies...and light winds
at lower elevations will mean cool overnight lows. Patchy frost is
likely in the coldest interior valleys late Sunday night/early
Monday. And local frosty conditions may continue during the late
night and early morning hours through at least midweek.
The upper ridge is forecast to begin breaking down and moving to
the east by Thursday. However...Thanksgiving is expected to still
be a dry and mild day...just a bit cooler than Tuesday and
Wednesday. The models agree that a Pacific weather system will
spread rain into our area late in the week...by Friday or Friday
night. Also...the longer range models indicate this could be the
start of a significant pattern change with more wet weather to
follow into the early part of December.
Aviation...as of 10:45 PM PST Saturday...we're seeing signs of
fog developing in the East Bay...kccr for instance reports 2 miles.
On the central coast kwvi now reports 1/4 mile visibility. Surface
high pressure is building over northermost California which will soon be
followed by pressure rises over the Great Basin early Sunday morning
..raising the wmc-sfo gradient to approx 6 mb. Over the North Bay the
northerly gradient from uki-sts is 2 mb...sufficient to sustain
enough wind to prevent fog formation in the area as long as the
gradient does not weaken overnight. The 00z NAM model under-forecasted
the present gradient by 1 mb...correcting for this the 2 mb gradient
should hold through early Sun morning. Based on this decided to
issue an amdendment for the ksts 06z taf to reduce the duration of
IFR...due to forecasted fog...down to a tempo group from 12z to
16z Sunday morning. Elsewhere fog patches will have a better chance
of persisting...watch out for quickly reduced visibilities very late tonight
and early Sun morning.
Vicinity of ksfo...moderate to high confidence VFR forecast for ksfo
..mixing westerly winds should help overnight.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...less certain (low confidence) that
the Monterey area terminals will hold onto MVFR/VFR overnight.
Satellite pictures Show Low cloud cover and fog patches from
about Fort Ord north to Watsonville.
Marine...as of 8:40 PM PST Saturday...high pressure over the
coastal waters will lead to a period of dry weather from early to
middle week...including the Thanksgiving Holiday. Building northwest
swell are expected Saturday evening into Sunday morning before
tapering off late Sunday.
... Reyes to Pigeon pt 0-10 nm until 1 am
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 1 am
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm until 1 am
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
Public forecast: dykema
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