Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
940 PM PST Thursday Dec 12 2013
Discussion...as of 8:06 PM PST Thursday...satellite imagery
reveals a band of high clouds spreading across the district ahead
of a weak shortwave that is currently moving inland over northern
California. This system will mainly bring an increase in high
clouds and a slight increase in northwesterly winds. No
precipitation is expected. Temperatures remain within a few degree
of 24 hours ago with overnight lows forecast to be slightly warmer
tonight. The increase in cloud cover will help insulate the region
a bit this evening. However at the rate this band of clouds is
moving it may be out of the area shortly after midnight. Therefore
the coldest inland valleys of the North Bay and southern Salinas
valley will likely see patchy frost once again.
Temperatures are forecast to begin rebounding this weekend as a
ridge of high pressure builds over the eastern Pacific and western
U.S. The surface high building over the eastern Pacific is
anticipated ridge across the Pacific northwest and into the Great
Basin producing another weak offshore wind event. 850 mb temperatures are
expected to reach 16 degrees c on Monday with 500 mb heights
around 586 dm. This will translate into unseasonably warm highs
across the district. High are expected to climb into the middle 70s
over the warmest inland valleys with upper 60s expected near the
coast for Monday and Tuesday of next week.
Model solutions diverge by midweek as they try to resolve what
will happen with an upper level low meandering over the eastern
Pacific. The low in question is currently spinning near 30n 136w
and is forecast to merge with another low that is approx. 600 nm
to the south. Once the two systems merge on Friday they are
prognosticated to move slowly northward. Models have not come to a
consensus as to the timing or trajectory of this low. However the
region should anticipate temperatures to cool to more seasonable
temperatures late in the week as the ridge that is expected to
bring the above average temperatures breaks down ahead of an
approaching upper level trough.
No rain is currently in the forecast...however with model
uncertainty it can not be ruled out.
Aviation...as of 9:40 PM PST Thursday...a weak cold front was
dissipating as it moved into northern California late on Thursday
evening. Light onshore flow and patchy coastal low clouds have
developed ahead of this front. Onshore flow will remain very light
overnight and expect low clouds to remain confined to areas near
the ocean and not affect the terminals. Confidence moderate.
Therefore...VFR conditions are forecast from tonight through
Friday evening. Winds will remain light...less than 10 knots.
Vicinity of ksfo...VFR with light winds. Few-scattered low clouds late
tonight into early Friday...but VFR conditions expected to
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...few-sct low clouds late tonight
into early Friday and there is a slight chance of IFR ceilings between
11z and 16z Friday morning. But VFR conditions are likely to prevail
through the forecast period. Light winds.
... Pinos to pt Piedras Blancas 0-10 nm from 3 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm from 3 am
Public forecast: CW
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