Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1011 am PST Wednesday Dec 17 2014
Synopsis...a weak system will move across the region and bring
isolated to scattered showers. Another weak system will affect
the area Friday and Friday night. High pressure to build over the
west this weekend and will bring a drying trend to the area well
into next week.
Discussion...as of 10:05 am PST Wednesday...isolated showers
continue over portions of the region this morning as a weak
middle/upper level system approaches the coast. Expecting these
showers to increase in coverage through the afternoon and early
evening hours as the weak disturbance moves inland. Thus...have
increased chances of precipitation for this afternoon and evening.
Generally speaking...rainfall amounts are forecast to remain light
today...especially compared to the rainfall totals from the
previous systems over the past week. Many locations are forecast
to receive between 0.10" to 0.15" of additional rainfall with up
to 0.25" possible in the higher elevations.
Previous discussion...as of 3:26 am PST Wednesday...radar loops show
showers are decreasing across the district. Currently light
showers can be seen moving across Marin County into Alameda and
Contra Costa counties. This shower activity will continue to
diminish by daybreak. Most of today should see a brief break in
the rain...but another system is forecast to approach the area
this afternoon spreading light rain across most areas overnight.
Less than a quarter of an inch is anticipated. After this system
moves through...the rest of Thursday is expected to be dry.
Another weak system is prognosticated to brush across the northern part
of the state on Friday with a half inch or less expected.
On Saturday high pressure aloft will begin edging eastward over
the state and pushing the storm track to the north. This will
usher in a drying trend that could persist until or beyond
Christmas day. The 00z GFS keeps the ridge strong over the state
through the end of the period. However the European model (ecmwf) and the Gem both
bring an inside slider across northern California late Wednesday
and Thursday which would bring cool...showery weather to the area
Aviation...as of 13:00 am PST Tuesday...the infrared satellite is
showing a weak storm system pushing towards the coast this
morning. Southeasterly winds are expected to prevail ahead of this
system becoming more southerly overnight. Light rain should reach
the terminals by late morning early afternoon. A period of
moderate rain is anticipated as the storm system passes over the
terminals between 0200 and 0600z tonight.
Vicinity of ksfo...advanced the timing of rainfall to be a few
hours earlier than previous forecast. Steady showers are
anticipated to begin around 2100z with a period of moderate rain
anticipated between 0200 and 0600z this evening. Southeasterly
winds are anticipated to prevail with this system reaching 8 to 12
knots as the system draws closer.
Confidence is moderate.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR is anticipated to persist into
the afternoon hours with showers possible by late morning. Light
rain and MVFR ceilings are anticipated to begin around 2300z with a
period of moderate rain expected between 0200 and 0600z. Southerly winds
are anticipated to reach 5 to 10 knots as the storm system passes
over the area.
Confidence is moderate.
Marine...as of 09:43 am PST Wednesday...west and northwest winds
will prevail along the central coast today as a cold front exits
the region. Winds will become more southerly as another storm
system approaches the region. Moderate northwest to west swells
will impact the coastal waters through Thursday. A long period
northwest swell will increase Friday and next weekend.
... Pt to pt pinos 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...rough bar advisory for sf bar until 3 PM
Public forecast: rgass
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