Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1136 am PDT Monday may 25 2015
Synopsis...cooler than normal weather...along with widespread
night and morning low clouds...will continue through Tuesday. Warmer
conditions are expected during the second half of the
week...especially for inland areas. However...coastal areas will
remain seasonably cool as onshore flow persists.
Discussion...as of 9:00 am PDT Monday...widespread clouds this
morning across almost all of our County Warning Area. In fact...compared to
yesterday the clouds extend farther inland and ot the north.
Interesting to note that around coastal Monterey County some
breaks are noted in the overall flow so quite possible that some
coastal spots there could see sunshine before San Jose or even
the far inland East Bay areas. Due to the clouds...marine layer
over 3000 feet...plus moderate onshore flow at the surface
temperatures will remain cooler than normal. Highs will mostly be
upper 50s to middle 60s at the coast with upper 60s to middle 70s for
most inland spots.
Models continue to bring a ridge of high pressure back to our area
later this week along with much warmer 850mb temperatures. Highs will
jump back into the 80s for many inland locations especially by Friday.
Coastal areas will see only limited warming as the flow off the
cool ocean water will keep the hotter weather at Bay.
Previous discussion...cooler than normal weather conditions...which have
persisted across the San Francisco Bay area and Monterey Bay area
for the past three weeks...will continue for at least a few more
days. Although an upper ridge has developed offshore along
135w...an upper low is settling into the Pacific northwest and helping to
maintain a deep marine layer across our area. And...cool marine
air is flowing well inland thanks to a persistent onshore flow.
Little change is expected through Tuesday. Widespread night and
morning low clouds will persist...along with patchy drizzle near
the ocean. Daytime temperatures will remain in the upper 50s along
the immediate coast where little or no afternoon sun is expected.
Afternoon clearing is expected inland...but high temperatures will
continue to be at least five degrees below normal in most
The models have been consistent in moving the upper ridge to the
east by midweek...with the ridge axis position forecast to be over
the West Coast by late Thursday. As the ridge builds over California
during the second half of the week...look for the marine layer to
be compressed and temperatures to rise...especially inland...as
the airmass warms aloft and marine air influence dwindles. Inland
temperatures are forecast to rise a few degrees above normal by
Thursday and Friday when 80s will finally return to locations like
Livermore...Gilroy and Calistoga. A shallow...but
persistent...marine layer along with continued onshore flow will
mean the coastal strip will see much less warming compared to
inland areas later this week.
Warm conditions will continue into at least the first part of next
weekend. But the ridge is forecast to move eastward over the
weekend as a trough approaches the West Coast. This will mean
cooler conditions by Sunday.
Other than patchy late night and morning coastal drizzle the next
few days...no precipitation is forecast through next weekend.
Aviation...as of 11:30 am PDT Monday...for 18z tafs. The marine
stratus deck is thinning out this morning and several holes of
clearing are evident on satellite imagery. MVFR ceilings will remain
through the day for areas with the strongest coastal influence...
including ksfo and kmry. Onshore flow will be light to moderate
with speeds 10 to 15 knots this afternoon and gusts up to 20 knots
possible. MVFR/IFR ceilings return this evening/tonight for all
Vicinity of ksfo... mixing out over the South Bay is spreading
northward towards the terminal this morning. Expect to see
clearing stall just short of the terminal as moist onshore flow
through the San Bruno gap will keep MVFR ceiling status quo over the
terminal. Ceilings may gradually rise from 1500ft to 2000ft through
the day before gradually descending after 03z Tuesday.
Ksfo bridge approach... clearing over the South Bay has lead to
VFR ceilings over ksmb with only a few clouds at or above 2000 feet on most of
Monterey Bay area terminals... broken/overcast 1500-2000 feet through most
of the day. Satellite imagery shows breaks in clouds upstream of
the peninsula so intermittent VFR/scattered possible during the
afternoon. Light to moderate onshore flow.
Marine...as of 11:13 am PDT Monday...northwest winds persist over
the central California coastal waters today. Very localized areas
of squared seas possible in the northern outer waters today. Winds
weaken and back towards the west through midweek then veer back
towards the northwest and increase late in the week. Predominately
gentle seas through the period.
... Bay north of the Bay Bridge from noon
Public forecast: Bell/dykema
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