Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
453 am PDT Sat may 30 2015
Synopsis...seasonable weather today with temperatures 60s
coast...70s around the Bay and some 80s well inland. As the marine
layer Burns off today high clouds will be on the increase ahead of
an incoming weather system. Slight cooling trend on Sunday as the
system stays off the coast and brings only a slight chance of
showers to the far North Bay. Zonal flow Monday through most of
next week will keep temperatures on the cool side of normal with
dry weather and widespread night and morning stratus.
Discussion...as of 3:21 am PDT Saturday...the marine layer is
compressing with The Fort Ord profiler at around 1000 feet. Dense
fog of 1/4 mile or less is now being reported at Watsonville and
Monterey and further evidence of the compressed layer. Given the
shallow nature of the marine layer it should mix out fairly
quickly around the Bay. However there are some increasing middle and
high clouds associated with an upper trough out near 35n/140w that
may inhibit burn off closer to the coast. The inland valleys
should be able to warm into the 80s but 60s and 70s will continue
to be the rule coast and bays.
Incoming upper low is fairly robust on Sunday but main rain shield
will stay off shore and then shift north towards Cape Mendocino as
it weakens. Cant completely rule out a stray North Bay shower but
main impact will be some increasing clouds...deeper marine layer
and cooler inland temperatures for Sunday afternoon. The Bay area will
stay in the warm core of the surface front and low so no significant
synoptic cooling but a robust seabreeze Sunday afternoon will
usher cooler marine air into the Delta and far East Bay by Sunday
Will be following the European model (ecmwf) solution for the middle and long range
which keeps the flow zonal early in the week and then shows upper
troughing middle to late week. This will keep temperatures near or
slightly below normal for the first week of June...similar to what
we saw much of may. Other than coastal drizzle the forecast
remains dry in the long range.
Aviation...as of 4:45 am PDT Saturday... high pressure with significant
subsidence aloft is resulting in a compressed marine layer and widespread
IFR ceilings this morning. Cloud bases are ranging from the surface to 1000
feet with fog being reported at kmry. The ceilometer at kmry is out
this morning... but visibility sensor and manual observations
confirm fog with likely vv001-vv002 ceilings this morning. Fort Ord
profiler and goesw satellite product indicating cloud thickness is
around 500 to 1000 feet which is thinner than previous morning. Will
likely see early mix out this morning due to shallower layer and
additional mixing. Drizzle possible along the coast. IFR ceilings
Vicinity of ksfo...IFR ceilings clearing after 18z. Onshore
winds through the day with gusts up to 25 knots this afternoon.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...IFR ceilings clearing after 18z at sns.
Low confidence for mry as the ceilings may become scattered in the afternoon
allowing for some brief VFR conditions.
Marine...as of 04:25 am PDT Saturday...high pressure shifts
inland and is replaced by a weak low pressure over the coastal
waters. Winds weaken through the weekend with the strongest winds
through the northern San Francisco Bay... Sonoma coastline... and
Big Sur coastline. Northwest winds increase and seas build midweek
into next weekend.
Public forecast: rww
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