Scientific Forecaster Discussion
fxus66 kmtr 162150
Area forecast discussion
National Weather Service San Francisco Bay area
150 PM PST Mon Jan 16 2017
Synopsis...dry weather will continue through Tuesday. An active
weather pattern returns midweek and persist into next weekend as
a series of storm systems impact California. Moderate to heavy
rainfall will be likely at times as well as locally strong and
gusty winds associated with the passage of each system.
Discussion...as of 01:47 PM PST Monday...a patch of low clouds
remain over the northern portion of the Sonoma Valley this
afternoon with temperatures beneath the cloud cover hold in the
40s. Do see signs of these clouds burning off and should allow for
additional warming through the afternoon before cooling after
sunset. Elsewhere, widespread 50s reported over the region under
mostly sunny conditions. Tonight, patchy fog and low clouds will
likely return to the North Bay valleys and around the Delta as
well. Could even see low clouds develop around the San Francisco
Bay and into the South Bay. Overall, conditions will be similar to
the past few days.
The forecast keeps conditions dry through Tuesday and likely even
into Tuesday night ahead of our next approaching system. The models
are in good agreement with widespread rainfall associated with a
frontal boundary spreading from north to south across the region
during the day Wednesday. Ahead of and along the boundary, southerly
winds will increase and become gusty at times. The strongest winds
and heaviest rainfall will likely occur during a short (3-6 hour)
period of time as the progressive system passes through. This should
help limit the overall Hydro and wind impacts across the region.
None the less, wind gusts up to 40 miles per hour will be possible in the lower
elevations with gusts upwards of 50 miles per hour in the higher, typically
In wake of the first frontal passage, winds will diminish and
widespread rains will turn to lingering showers Wednesday night into
Thursday. A second system will then bring another round of
widespread precipitation from Thursday night into Friday. As with
the first system, winds will increase and become gusty at times
during the overnight and early morning hours as the system passes
through. Rainfall amounts from these two systems will be greatest in
the coastal ranges where 2.00" to 4.00" will be possible with
isolated amounts upwards of 5.00". Meanwhile, lower elevations will
likely pick up between 0.50" to 2.00" (greatest along the coast and
in the north bay) while some of the driest inland valley locations
may receive less that 0.50". Lingering showers are then likely from
Friday night into much of Saturday. Snow levels are also forecast to
drop in wake of the second system and may result in some snow showers
in the higher peaks across the region.
A third system is then forecast to sweep through Saturday night into
Sunday and will bring another around of widespread rainfall. The
passage of this system should also be preceded by locally strong and
gusty winds. At this time, rainfall amounts are forecast to be
similar to the first two systems, yet may result in locally higher
totals. Will continue to monitor the latest guidance and update the
forecast as we get further into the workweek.
Aviation...as of 9:36 am PST Monday...mostly VFR this morning as
widespread fog/clouds did not form. However, ksts has dense fog
and ksjc has 3sm br. Do expect a gradual thinning of the lingering
fog. VFR this afternoon with some patchy haze...could cause some
slantwise vsby issues. Low conf for tonight...some of the hi-res
models are hinting as a poss fog event. The WRF shows lighter
offshore flow with higher sfc relative humidity...especially in the Delta and
Bay. Conf is not high enough to add for koak or ksfo, but will
have to watch closely between now and then.
Vicinity of ksfo....VFR through the period with high clouds. Will
have to watch for some haze today and poss fog tonight.
Sfo bridge approach...similar to sfo.
Monterey Bay terminals...VFR.
Marine...as of 08:33 am PST Monday...light to moderate northerly
winds will persist along the central coast as high pressure
remains off the West Coast. A moderate westerly swell with a
moderate period will also persist today. A front will approach
late Tuesday night into Wednesday with increasing south winds
that will turn southwest by Wednesday night. Large northwest swell will
build midweek and beyond with potential for 20 foot plus seas by
Friday and into the weekend with at least two more strong storms
passing over the waters.
Public forecast: rgass
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