Scientific Forecaster Discussion
fxus66 kmtr 151206
Area forecast discussion
National Weather Service San Francisco Bay area
406 am PST Fri Nov 15 2019
Synopsis...a weak front will move through the North Bay this
morning with some light showers or sprinkles possible. Elsewhere
skies will be cloudy this morning then turning partly sunny by
this afternoon. High pressure builds Saturday through Monday with
a warming and drying trend as light offshore winds develop in the
hills. Cooling by Tuesday as the ridge breaks down as the next
front drops through the Bay area by Wednesday but the best rain
chances stay over the Sierra and eventually Southern California.
Discussion...as of 3:29 am PST Friday...for the first time in a
while we've put the radar into precip Mode. A weak front is
currently draped across Mendocino County and shifting towards
Sonoma County. Elevated returns are showing up over the coastal
waters west of Bodega Bay with some light showers or sprinkles
possible this morning, mainly across Sonoma County. So far not
seeing any tips of the bucket but there is plenty of low level
moisture and enough synoptic lift to generate some drizzle/light
showers/sprinkles through about 18z this morning. Other locations
will start out cloudy, with some dense pockets of fog. There will
be a trend towards partly sunny skies by midday or early afternoon
as high pressure quickly builds over the region.
The surface pattern then supports some light offshore winds
developing in the hills overnight. The ridge will be building in
so quick and offshore winds light enough that residual clouds will
likely persist near the coast and coastal valleys into Saturday
Noted warming trend develops Saturday through the weekend with
afternoon highs back into the 70s, warmest readings on Sunday as
the ridge peaks. So the stage is set for an ideal Bay area weekend
with plenty of sunshine and comfy afternoon temps in the 70s.
Overnight lows wont be as cold as recently as the airmass is more
moist with higher dewpoints allowing for milder nights in the 40s
Monday still looking like a nice day but the ridge weakens
slightly and offshore flow eases by afternoon as the next Pacific
trough approaches the region.
Much cooler by Tuesday as a mainly dry upper trough and surface
cold front will move through the Bay area. The best chance for
precip will be over the Sierra though cant completely rule out
some local showers. Though nothing of significance is forecast at
The boundary will drop into socal and then tap into some deeper
moisture such that the Sierra and socal could eventually get some
moderate precip while the Bay area remains mostly dry.
The long range trends then suggest dry and seasonable later next
week and into next weekend. Looking out towards Thanksgiving the
pna ensembles show more members trending negative (cooler and
wetter pattern for norcal). This then gives some credence to some
of the long range ensembles (eps/gefs) showing precip by the last
week of the month.
Aviation...as of 4:07 am PST Friday...for 12z tafs. Mainly MVFR
cigs this morning as another weak front approaches. The front is
weakening and will dissipate as it moves inland. The North Bay
terminals may see some patchy drizzle or brief light rain this
morning but the other taf sites are expected to remain dry. The
front will bring lowering cigs but the terminals will remain MVFR.
After the front passes through will see some scattering out of
the clouds late this afternoon. As high pressure begins to build
overhead this evening, low level moisture will persist with cigs
reforming and lowering overnight. Fog developing across the North
Bay valleys overnight. Winds today are generally light with west
winds developing this afternoon.
Vicinity of ksfo...MVFR cigs this morning with bases 2500-3000
feet. MVFR cigs may briefly scatter out early this afternoon. As
a weak front approaches will see lowering clouds this afternoon.
Scattered to possibly broken clouds will develop around 1000 feet around
20-22z. MVFR cigs persisting through the evening with bases
potentially lowering to IFR overnight tonight. Light winds this
morning becoming westerly and breezy this afternoon.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...light winds this morning becoming onshore
this afternoon. MVFR cigs with bases around 3000 feet gradually
scattering out this morning. Will see a return to MVFR cigs this
evening with bases lowering to 1000-2000 feet overnight.
Marine...as of 03:03 am PST Friday...light rain along a cold
front will occur this morning across the northern waters. Winds
will shift to the northwest today behind a cold front and
gradually increase through tonight. A relatively large, long
period northwest swell will increase this morning and persist
through Saturday. Wave heights around 10 feet with breezy to
gusty northwest winds will create hazardous conditions for small
crafts today through Saturday.
... Pt to pt pinos 0-10 nm from 3 PM
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm from 9 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm from 9 am
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm from 9 am
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm from 3 PM
Public forecast: rww
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