Scientific Forecaster Discussion
fxus66 kmtr 271151
Area forecast discussion
National Weather Service San Francisco Bay area
451 am PDT Sat may 27 2017
Synopsis...dry with seasonable temperatures for much of the
Holiday weekend. The next trough and associated cooling trend
arrives Tuesday and Wednesday with long range trends indicating
dry and benign weather pattern.
Discussion...as of 4:00 am PDT Saturday...cloud coverage is much
more patchy this morning compared to 24 hours ago with profiler
data showing a weak inversion above 4000 feet. At this time clouds
are most numerous around sf Bay, Marin County and the Santa Clara
Valley. Clouds will likely continue to expand through sunrise but
given the patchy nature inland and cooling aloft expect skies to
turn mostly sunny much earlier today as high pressure builds. The
increased sunshine will lead to a noted warming trend today,
especially after such a cool Friday where most climate sites
stayed in the 60s or struggled to reach around 70 even inland. It
should be a nice start to the Holiday weekend with widspread 70s
away from the coast and even some lower 80s for the warmest inland
spots while the coast should see peaks of sunshine with beach
temps in the lower 60s.
High pressure will nose over the region on Sunday with 850 mb
temps this morning around 12 celsius approaching 18 celsius inland
on Sunday afternoon. This should lead to a pronounced warming
trend for inland areas with more widespread 80s.
In general weather should be nice for Memorial Day but increasing
onshore flow ahead of the next trough will likely bring some gusty
west winds to the beaches with increased marine clouds. Inland
areas should enjoy another sunny and seasonably warm afternoon on
Monday for those looking to enjoy outdoor activities.
A fairly well defined upper trough will approach Cape Mendocino by
early Tuesday morning and likely bring some coastal drizzle and
increased marine push of clouds for Tuesday morning. In addition
temperatures will trend cooler again with a synoptically cooler
airmass aloft. Surface pressure gradients will increase such that
breezy west winds are forecast both Tuesday and weds in what will
likely be a fairly cool end to the month.
ECMWF shows dry with high pressure for the start of June into the
first weekend of the month.
Aviation...as of 4:45 am PDT Saturday...stratus deck retreated
offshore late last evening and has slowly been building back
towards the coast over the last few hours. A mixed bag of VFR to
MVFR cigs currently, but expect to see deteriorating ceilings up
to and around sunrise, then persist around those levels for around
an hour or two into the morning. Otherwise, light winds today,
with some breezy west winds along the immediate coastline by the
afternoon. For tonight, subsidence aloft will contribute to a
compressed marine layer, reducing the inland intrusion extent,
but bringing much lower LIFR to IFR cigs. In addition, onshore
winds increase tomorrow.
Vicinity of ksfo...stratus deck expanding and thickening during
the pre dawn hours. Currently VFR but would not be surprised to
see MVFR by 12-13z... persisting into or just beyond sunrise. Low
confidence due to discontinuity of marine layer and lack of
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...patchy cigs in the predawn hours will
become increasingly lower and more widespread as additional
moisture is advected onshore. MVFR cigs by sunrise, which will
linger into the mid morning. Model guidance is sketchy on a return
time of stratus for later today, with a return possible as early
as 01z. Light onshore winds.
Marine...as of 04:43 am PDT Saturday...light west winds through
the morning. Northwest winds will begin to increase later today
and through the Memorial Day weekend as high pressure builds
offshore. The swell train will be generally 5 foot or less
through the forecast period so wind waves will dominate the sea
... Pinos to pt Piedras Blancas 0-10 nm from 3 PM
Small Craft Advisory...mry Bay from 3 PM
Public forecast: rww
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