Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
343 am PST Sat Dec 27 2014
..colder weather expected Tuesday and Wednesday with the
potential for a strong offshore wind event...
Synopsis...freezing temperatures primarily over inland areas will
modify slightly the next couple of nights. However...the chilly
airmass will remain over central California through much of the
upcoming week with a reinforcing shot of cold air arriving late
Tuesday and Wednesday. This next system has the potential of
bringing strong gusty offshore winds especially to the north and
East Bay and Santa Cruz Mountains.
Discussion...as of 02:58 am PST Saturday...the freeze warning for
interior Monterey and San Benito counties is on track this morning
with Pinnacles at 29 degrees and Hernandez down to 26 degrees. Most
inland valley locations closer to the coast and Bay reporting
temperatures in the middle to upper 30s with locations exposed to
offshore east winds mainly in the 40s. Urban Bay area temperatures
are generally in the 40s. Would expect winds to decouple other
than ridgetops and mountains gaps around sunrise with a quick drop
in temperatures in many valley locations.
Trough approaching Vancouver Island digging southeastward and models
in good agreement shearing this feature across the Great Basin
tonight and Sunday. High clouds will drift across the area today
with patchy middle level clouds as well tonight. Forecast model
soundings indicate some increase in precipitable water tonight
associated with the middle and higher level moisture and should be
enough to raise tonights lows a couple of degrees. Not
anticipating a need to renew the freeze warning again tonight
given the slightly warmer readings. Areas of inland frost are
still expected tonight with even patchy frost in some coastal
valleys. Anticipating slightly higher dew points tonight which
could generate a few patches of fog North Bay by Sunday morning.
A major cold airmass is forecast to push southward from Canada
early in the week carving out a deep trough over the far west. Main
shot of cold upper level energy is projected to dig into central
California Tuesday and Wednesday and models all support this
solution. Central coast winds will shift from weakening offshore
flow to boundary layer winds paralleling the coast or even turning
onshore Sunday night and Monday and increasing. Main impact will
be increasing boundary layer humidity and more areas of morning
fog on Monday...and reflected this trend in the grid forecasts
with the addition of patchy fog at least into the North Bay and
parts of East Bay. Would not be surprised to see fog or low clouds
develop in the Bay area as well.
As system digs southward and forms a closed low over central
California Tuesday would expect to see a slight chance of showers
with lowering snow levels and the potential for a dusting of snow
at least down to 3000 feet. However...the main message with this
system will be wind and not precipitation with the drier overland
trajectory. The main threat for showers will be the Santa Lucia
mountains and interior Monterey County mountains as cold advection
and northwest to north winds drive low level moisture over the
elevated terrain. The airmass will dry quickly behind the trough
with strong gusty northeast flow developing. Could easily see Wind
Advisory conditions Tuesday into early Wednesday especially north
and East Bay. Inland areas should observe widespread freezing
conditions especially as winds decrease Wednesday night and
The dry pattern continues into next weekend with a warming trend
expected late in the week as the ridge edges eastward toward the
coast. There are hints of jet stream energy attempting to undercut
the ridge beyond next weekend...but confidence is very low at this
time. European model (ecmwf) is not as robust with this scenario and maintains a
strong ridge with minimal Pacific energy breaking it down...and a
continuation of digging systems into the Great Basin from Canada.
Aviation...as of 9:35 PM PST Friday...a cool dry airmass will
remain over the region providing clear skies across area
terminals. Light winds will persist through the forecast period.
Vicinity of ksfo...VFR.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
Marine...as of 9:00 PM PST Friday...light north winds are
anticipated to veer east to southeast tonight and Saturday. Winds
are forecast to turn northerly and strengthen Sunday night as a
weather system slides south across the state. Moderate north winds
will persist through the first half of the week. Northwest swell
will prevail through the weekend then gradually diminish.
... Warning...southern Salinas valleys and interior
mountains of Monterey and San Benito counties
Public forecast: kbb
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