Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
857 PM PST Wednesday Nov 26 2014
..periods of rain forecast from late Friday through the middle of
..potential heavy rain...Hydro concerns...and strong and gusty
winds during the first half of next week...
Synopsis...high pressure will maintain dry and mild weather
through Thanksgiving day. Rain will develop in the North Bay by
late Friday and press south through most of the rest of the region
Friday night into Saturday. Periods of rain are expected to continue
into Sunday. More rain...possibly heavy...is then likely from late
Monday through the middle of next week.
Discussion...as of 8:55 PM PST Wednesday...high pressure and
light offshore flow continued to generate dry and mild weather
across our region today. Highs today were generally in the 60s and
lower 70s across the San Francisco Bay area and in the 70s to
lower 80s from Monterey Bay southward. Highs were anywhere from 5
to 15 degrees above normal for the date and two daily high
temperature records were tied...at Oakland museum (72) and Salinas
No significant changes are forecast for Thanksgiving day.
Temperatures will cool a bit as the upper level ridge begins to
weaken and shift east. Most of the cooling will be confined to the
northern portion of our area where light onshore flow will develop
by afternoon...and where periods of high clouds will filter the sun.
The much-anticipated pattern change is still on track...with
periods of rain expected from late Friday through the weekend and
on into next week. The ingredients are in place for significant
rainfall in our area from the weekend on into next week...with the
longwave trough position forecast to remain just off the West
Coast...and with ample moisture availability. The frontal boundary
to our northwest will initially remain stalled well to the north
of our area...blocked by the slowly weakening ridge. But a
shortwave trough currently seen on infrared satellite as a comma cloud
our near 35n/148w...will push the frontal boundary to the
southeast and into our North Bay counties by late Friday. Rainfall
is then forecast to spread south through the rest of the sf Bay
area on Friday night...and into the Monterey Bay area by Saturday
morning. The boundary will then stall out and weaken on Saturday
evening as shortwave ridging develops ahead of the next incoming
shortwave. That second shortwave will trigger an increase in
rainfall intensity by late Saturday night into Sunday.
Rainfall from late Friday through Sunday will mostly be light to
moderate in intensity but could be briefly heavy at
times...especially in the coastal mountains. Southerly winds will
be gusty at times from Friday night through the weekend...but
should remain below advisory levels.
More significant rainfall and winds are then possible early next
week as a more powerful storm system potentially impacts
California. That system is currently developing in the Bering Sea
and is forecast to drop southeast and form a cutoff low offshore
along 140w over the weekend. The low is then forecast to move
gradually to the east early next week and potentially produce
periods of heavy rain and strong winds across our region from late
Monday through Tuesday night. The models agree on the general
idea...although there is disagreement on timing of heaviest
precipitation. The upshot is that our area could see some Hydro
issues...including minor Urban and Small Stream flooding...during
the first half of next week along with strong and gusty winds.
Aviation...as of 3:40 PM PST Wednesday...VFR conditions with
light winds through the forecast period. High cloud continue to
stream in over the North Bay this evening. These insulating clouds
will work against fog development... however cant quite rule out
fog at ksts... but may do so at the 06z tafs.
Vicinity of ksfo...VFR.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR.
Marine...as of 03:33 PM PST Wednesday...southerly winds will
prevail north of Pigeon Point and northerly winds will prevail
south of Pigeon Point through Friday. Southerly flow will develop
over all of the coastal waters this weekend as a storm system
begins to impact the region. Unsettled weather is expected Friday
into early next week with periods of rain and gusty winds. The sea
state will likely deteriorate rapidly early next week as the
strongest storm moves through.
Public forecast: dykema
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