Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
433 am PST Friday Nov 27 2015
Synopsis...dry and cool weather can be expected through the
weekend. Temperatures will begin to moderate early next week.
There is also a chance of rain beginning late Monday.
Discussion...as of 3:30 am PST Friday...upper level low over
Nevada is bringing a dry and cold airmass to the area with flow
from the north to northeast. Winds have persisted in the North Bay
and parts of the sfo Bay area through the evening and kept
temperatures well above freezing. Winds may still drop off by
early morning allowing temperatures to drop rapidly but it is
looking less likely there will be subfreezing temperatures lasting
more than a couple of hours. Freeze warnings will be dropped for
the rest of tonight in the north and East Bay and frost advisories
dropped for the sfo Bay area. Freeze warnings remain in effect
through 9 am for the South Bay interior as winds there are lighter
and current temperatures are colder. Frost advisory will remain
for the mry Bay area as well.
The upper low will remain nearly stationary through Saturday
before moving east on Sunday. Clear and cool weather is expected
today with highs in the 50s. Winds will likely hold up through
Saturday morning before decreasing Saturday night. Minimum
temperature forecast will be tricky again tonight depending on the
winds. Minimum temperatures Saturday night may be the coldest
night of the week if the winds decrease as forecast.
An upper level ridge moves over the West Coast Sunday. The flow
will become more westerly and temperatures will start to moderate.
A weak system will dissipate as it bumps up against the ridge but
it will bring slight chance of rain Monday or Tuesday. Another
system will bring possibly a better a chance of rain next
Wednesday or Thursday but rainfall amounts are expected to be
Aviation...as of 4:33 am PST Friday...offshore wind coupled with
cyclonic flow wrapping around a large and wobbly low center over
California/NV/UT this morning. North-NE winds gusty in the North Bay and parts
of the East Bay as well. Surface winds are mostly decoupled from
winds aloft over the South Bay and across the north central coast.
Ksts reporting continued wind gusts to near 30 knots. Appears to
be just enough mixing around the Bay area thus low level wind shear not indicated
in 12z tafs... but pilot weather reports very helpful and will monitor winds.
Thought is directional shear is not likely a problem...but there
may be isolated pockets of speed shear in and around the Bay area
through sunrise this morning. 12z Oakland sounding shows a near
surface inversion based approx 400 feet off the ground. Otherwise
a dry air mass supporting high confidence VFR for the period.
Vicinity of ksfo...VFR. North-NE winds near 10 knots today.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR. Light offshore winds.
Marine...as of 3:18 am PST Friday...light winds and seas will
persist through the weekend. Winds and seas are expected to
increase beginning early next week as a weak frontal system moves
into the California coastal waters.
... Advisory...mry Bay area and Big Sur coast
freeze warning...southern interior valleys and
Public forecast: west pi
Visit US at www.Weather.Gov/sanfrancisco
Follow US on facebook and twitter at: