Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
454 PM PST sun Nov 29 2015
Synopsis...cold temperatures again tonight. Weak storm system
fizzles in North Bay tomorrow. Slight warming trend into midweek
then a wet and windy storm system early Thursday.
Discussion...as of 3:00 PM PST Sunday... the area saw another
round of frost and subfreezing temperatures this morning.
Temperatures dropped like a rock where winds were calm... with
temperatures in the upper teens to lower 20s in the North Bay... and
temperatures jumped in areas with higher mixing winds... such as
around the Monterey Bay. The winds are having such a tremendous
impact on temperatures primarily because the synoptic scale
pattern has been roughly been in a holding pattern the last
several days as a Rex block is over the western Continental U.S.. the
California coast has remained in the cold dry northeasterly flow
on the Lee side of this feature. This will change by tomorrow as
the Rex block over the western Continental U.S. Will be ejected from the
Great Basin and pushed east of The Rockies by tomorrow and we
should see a gradual warming trend into midweek. Temperatures
today are already running a few degrees warmer than yesterday.
Temperatures tonight are likely to be cold again... but a few
degrees warmer than last night. Winds are not expected to be
strong... however... an approaching upper low will cause increased
cloudiness tonight... which will keep the region somewhat
insulated. The timing...coverage...and thickness of this cloud
deck will be the driving factor for temperatures tonight. Have
decided to reissue a freeze warning for tonight as many inland
locations still look to be in the 25-32 range for Monday
A shortwave disturbance will approach the region later tomorrow
but this feature will fizzle out as it hits the dry air mass in
the wake of the Rex block. The main impact from the feature will
be an increase in clouds tomorrow. A few stray rain showers are
possible over the North Bay tomorrow before the system
degenerates. A weak ridge then develops for Tuesday and
Wednesday and will bring our daytime temperatures to near normal for
Medium term models have come into general agreement that a
stronger storm system will move into the region early Thursday.
This storm system currently looks sufficient to bring breezy winds
and moderate amounts of rain to the region. Precipitation amounts look to
range in the quarter of an inch to an inch range... with locally
higher amounts over elevated terrain.
Long term models show another storm system approaching about a
week out from now... next Sunday. Will need to keep an eye on
this... however... the midweek storm system looks to be the
strongest of the upcoming 3 disturbances.
Aviation...as of 4:45 PM PST Sunday...a dissipating front will
bring middle and high clouds to the area late tonight otherwise VFR
conditions through Monday. Light east to southeast winds through
Vicinity of ksfo...VFR.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR.
Marine...as of 8:22 am PST Sunday...light winds will continue
over the coastal waters today...except local moderate easterly
winds near the Golden Gate. Winds will turn southerly over the
northern waters tonight as a weak frontal system approaches. A
stronger Pacific weather system will generate moderate to strong
southerly winds by midweek. Seas will be light today and then
build tonight into Monday.
... Warning...inland zones until 9 am Monday
Public forecast: drp
aviation: west pi
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