Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
828 am PST sun Nov 23 2014
Synopsis...an upper level ridge will produce dry and mild weather
across the region through Thanksgiving day. Daytime temperatures
will warm well above normal by Tuesday. Nights will be
cool...especially in the valleys. A weather pattern change is
expected to occur late in the week...which will result in rain
chances by next weekend.
Discussion...as of 8:28 am PST Sunday...quiet weather in store for
today and most of the upcoming week. Some patchy dense fog this
morning has already burned off and skies are mostly sunny except
for some increasing high clouds over the North Bay region. Expect
comfortable afternoon highs in the 60s with a drier air mass in
place behind yesterdays frontal passage. The flow is
offshore...although not too strong with some northeast wind gusts
from 20 to 35 miles per hour in the East Bay hills.
For tonight expect mostly clear skies with cool overnight lows in
the 40s most locations except some upper 30s in the coldest
valleys of the North Bay and interior Monterey/San Benito. With an
offshore trend will need to monitor for any Tule fog that may try
and ooze into the region but in general it looks like Central
Valley fog will be confined to the southern San Joaquin which
should keep the Bay area mainly fog free.
High pressure will build Monday through Wednesday with sunny and
seasonably mild weather across the Bay area and most of the state.
From a travel perspective weather looks good for California. Look for
highs from the upper 60s to upper 70s with some light offshore
flow and 850 mb temperatures pushing 16-17 celsius.
On Thanksgiving day the ridge will flatten but weather looks nice
for outdoor plans with highs still in the 60s and plenty of sunshine.
Right now Friday looks to stay dry as well ahead of any pattern
change. Onshore flow with seasonable temperatures.
Models are trending towards a wetter solution by next weekend but
will wait for 12z guidance and address that in the afternoon
package. Some light rain chances look to return Saturday but
overall confidence remains medium at best at this time.
Previous discussion...as of 3:35 am PST Sunday...today is shaping up
to be a mostly sunny and mild day with highs mostly in the middle
60s. The low amplitude upper ridge currently centered offshore
along 135w is forecast to amplify and shift eastward over the next
few days. Subsidence under this ridge will warm and dry the
airmass over our region. 850 mb temperatures are forecast to rise from
7-8 degree c today to 15-16 degree c by midweek. In addition...light
offshore flow will persist through at least Tuesday...helping to
maintain a dry airmass over our area. These developments will
result in a warming trend over the next few days with high
temperatures reaching into the upper 60s to middle 70s range by
Tuesday...about 10 degrees warmer than normal. Daytime
temperatures will probably reach their peak on Tuesday and
The combination of clear skies...light winds...and a dry airmass
will mean cool nights. Patchy frost is likely in the coldest
inland valleys of the North Bay...as well as southern interior
Monterey County...late tonight and early Monday morning. Minimum
temperatures will gradually moderate through the week...but inland
valleys will continue to see temperatures dip into the middle and upper 30s
through at least midweek.
Fog should not be much of an issue after this morning...except
perhaps near the Delta.
The medium range models agree that a pattern change will begin to
develop late in the week. The upper ridge will start to break down
and move to the east by Thursday. However...the ridge will hold on
long enough to maintain dry and mild weather through
Thanksgiving...and possible into Friday as well. Daytime temperatures
will begin to cool by Thursday as the ridge weakens and light
onshore flow develops. Rain chances are forecast to begin in the
northern part of our area by late on Friday as a storm system
approaches California from the west. Rain chances will then develop across
most of the rest of the area Friday night into Saturday. Both the
European model (ecmwf) and GFS then bring a second round of heavier precipitation through
our area during the early part of next week as a deep upper trough
with ample moisture arrives along the California coast. This is still
beyond our seven day forecast period and obviously subject to
change. However...the model agreement is at least encouraging.
Aviation...as of 4:00 am PST Sunday...there has been patchy fog
in the East Bay interior as well as in the Salinas valley. Surface
high building into northern California will bring a light north to
northeast flow to the sfo Bay area. The fog is expected to stay
out of the sfo approach zone this morning as the flow has not
quite established itself. Less fog is expected Monday morning as
the airmass dries out even though the north to northeast flow
becomes established so fog will not be an issue for sfo and Oak.
Vicinity of ksfo...moderate to high confidence VFR forecast for ksfo.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...patchy fog around sns through 15z
with visibilities as low as 1/2 mile.
Marine...as of 08:10 am PST Sunday...high pressure off the
California coast extends into northern California and northern
Nevada. This will bring stronger winds to the southern waters
through Monday night. Winds will become light Tuesday and
Wednesday then switch to southeast Thursday as the high moves into
the Great Basin.
... Pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
Small Craft Advisory...rough bar advisory for sf bar
Public forecast: rww
aviation/marine: west pi
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