Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
924 am PST Friday Dec 26 2014
..much cooler temperatures expected tonight with patchy frost
in the valleys...
Synopsis...cold temperatures expected once again Friday night
into Saturday morning. These cold temperatures will result in wide
spread frost for many inland locations. Otherwise...dry weather
is expected to persist into the beginning of next week with cold
overnight temperatures possible once again by middle week.
Discussion...as of 9:24 am PST Friday...it was a cold start
around the forecast area this morning with many inland
temperatures falling into the low 30s and even 20s! Monterey
Airport fell to 37...Pinnacles National Monument fell to 27 and
Bradley reported 26 degrees at 7 am. Light offshore winds should
reinforce the cold airmass that is in place over our area which
will result temperatures falling a few degrees cooler tonight.
With this in mind will most likely issue a hard freeze warning for
our southern counties. The coldest temperatures anticipated to be
in the interior sections of Monterey and San Benito counties.
Our frost advisory criteria does not permit US to issue a frost
advisory for non urban areas after December 15th. However...due to
the cold crisp airmass expect wide spread frost to develop at many
locations overnight tonight.
The 0000z European model (ecmwf) along with the 1200z gfs40 and nam12 have
initialized well with the current synoptic pattern and remain in
good agreement through the next 84 hours. The forecast models are
suggesting another cold night tonight before the airmass modifies
permitting slightly warmer temperatures for Saturday night into
In the extended forecast both the 0000z European model (ecmwf) and 1200z gfs40 are
forecasting a cold storm system pushing into the Great Basin
states on Sunday. This cold storm system slides into northern and
central California on Tuesday. Unfortunately...model agreement
breaks down on the exact timing and trajectory of this storm
system. Depending on the track of the system our area could be in
for another round of cold temperatures by middle week with a
possibility of snow showers in the hills. We will be keeping an
eye on this developing weather story as it unfolds.
Aviation...as of 4:30 am PST Friday...a dry northerly wind flow
will continue for the period leading to VFR conditions. The acv-
sfo pressure gradient is almost 6 mb...in-line with the NAM model
forecasts for today. Nocturnal Delaware-coupling of the surface winds is
mostly found in the normally wind protected Bay area valleys while
Hill Top/mountain top winds are still fairly breezy with some
instances of surface wind to wind aloft linkage continuing in and
around the Bay area. For example the northwest-north-northwest winds at ksfo have
been slowly increasing since late last evening to a presently
sustained 20 knots. Vertical wind profiles not quite supportive of
non-convective low level wind shear but will monitor through day
Vicinity of ksfo...VFR.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
Marine...as of 4:13 am PST Friday...gusty north to northwest winds
will continue across the northern outer coastal waters. Elsewhere
winds will gradually diminish as the gradient relaxes through the
day. Moderate northwest swell will gradually diminish through the
weekend and into early next week. The weather will remain dry
through the weekend followed by a chance for showers by Monday and
Tuesday of next week.
... Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Public forecast: Larry
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