Scientific Forecaster Discussion
fxus66 kmtr 201744
Area forecast discussion
National Weather Service San Francisco Bay area
944 am PST Mon Nov 20 2017
Synopsis...a weather system will bring periods of light rain to
the North Bay and possibly San Francisco today. High pressure will
bring dry and warmer weather to the area Tuesday through Thursday.
The next chance of rain will be late this weekend.
Discussion...as of 08:52 am PST Monday...morning radar imagery
from kmux and Mt vaca radars continue to indicate light shower
activity across the North Bay. The showers are associated with
very moisture SW flow and weak isentropic lift along the 295 k
pressure level. Rainfall amount over the last few hours have been
a few hundredths across the North Bay. Current forecast for this
afternoon have showers north of the Golden Gate and see no reason
to change that. Locations south of the Golden Gate will be dry
this afternoon. No update is needed at this time.
Rain chances diminish tonight as a decent ridge builds over the
region ushering in well above normal temperatures.
Previous discussion...as of 3:15 am PST Monday...
Things will dry out tonight as the warm front lifts north. An
upper level trough deepening along 145w will cause an upper level
ridge to build over Southern California and Nevada. This will
keep rain north of the district while bringing warmer temperatures
Tuesday through Thursday. The warmest temperatures will be
Wednesday and Thursday with highs in the 70s to lower 80s in
Monterey and San Benito counties. Temperatures around the sfo Bay
area will warm into the upper 60s to lower 70s.
The ridge flattens on Friday and temperatures will cool off
slightly. Then the ridge moves a little to the east Saturday and
Sunday and the trough starts to move to the northeast. Medium
range models indicate a warm front will bring a chance of rain to
the North Bay Saturday night and most of the rest of the district
Sunday. Then another chance of rain Sunday night and Monday as the
Based on recent performances by the models...would not be surprised
if future model runs trend drier with the weekend system and track
it further north. In any case rainfall rates and amounts will be
Aviation...as of 9:42 am PST Monday...for 18z tafs. Cigs remain
VFR at all taf terminals but ksts, where MVFR cigs prevail. A few
rain showers are possible through the day today at ksts. Expect
MVFR cigs to continue through at least 00z, with intermittent VFR
possible. Elsewhere, ceiling heights are expected to remain above
3000 feet. Light southeast winds through the day, should stay
below 10 knots. Kept low level wind shear at ksts through 20z.
Vicinity of ksfo...light southeast winds will prevail, along with VFR.
Forecast still calls for dry runways. Could be some low
clouds/reduced visible before sunrise Tuesday, though not very
confidence with that occuring.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...Salinas valley continues to be the area
where southeast winds are the strongest this morning. Expect winds to
decrease this afternoon, once the winds switch out of the west-northwest.
Light winds expected at kmry. VFR expected through the forecast
Marine...as of 09:22 am PST Monday...high pressure to the south
will keep a very moist sub-tropical flow just north of the
coastal waters. Winds are expected to stay light to moderate out
of the south today, with the highest wind speeds remaining over
the northern coastal waters. By late week into early next week a
cold front will move southeastward over the coastal waters. Seas
are expected to remain light to moderate through the first part of
Public forecast: mm/west pi
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