Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
534 PM PDT Wednesday Oct 22 2014
Synopsis...dry weather conditions and partly cloudy skies are
expected tonight...but then on Thursday the weak tail end of an
approaching Pacific weather system will likely bring some light
rainfall to northernmost portions of our district. Friday looks to
be mostly sunny and mild...but then a somewhat wetter system
will move in on Saturday and spread rain chances across much of
our area. Dry conditions and seasonal temperatures are projected
for Sunday into the first part of next week.
Discussion...as of 3:05 PM PDT Wednesday...skies are clear to
partly cloudy with middle afternoon temperatures around the bays
generally running in the upper 60s to middle 70s...a couple of degrees
warmer than at the same time yesterday. Tonight...the weak tail
end of a Pacific weather system now moving into the Pacific
northwest will spread in increasing middle and high cloudiness over
more northern portions of our area. Then on Thursday...model solutions
indicate a likelihood of some rain south to near Bodega Bay...with
a slight chance as far south as about San Francisco. Rainfall totals
look to be quite light...except in the far northern coastal hills
of Sonoma County where local amounts up to the 1/3 to 1/2 inch
range are possible.
Any residual North Bay showers should taper off and end Thursday
night with dry conditions then expected district-wide on Friday
as a short wave upper level ridge temporarily builds in westward from
the interior. By late Friday night however...the next Pacific
weather system is expected to rapidly approach from the northwest.
Latest model output continues to indicate it will be both a bit
stronger and wetter than the one on Thursday...with a likelihood
of at least some light precipitation spreading as far south as the
Monterey Bay region by Saturday afternoon. Should also note that
both latest NAM deterministic model output soundings and surface based
cape values...and sref MUCAPE plumes...indicate a sufficient
possibility of convection Saturday afternoon over the North Bay to
warrant inclusion in the forecast of mention of a slight chance of
Here again Post frontal showers look to taper off and end pretty
quickly...with dry weather conditions returning across all but
possibly the easternmost margin of our area by Sunday morning. Dry
conditions and seasonal temperatures are expected across the
district through at least Monday night. Thereafter longer range
model solutions begin to diverge...with for example the 12z GFS
bringing in another weak system and light precipitation to the North Bay
on Tuesday while the European model (ecmwf) confines associated rainfall to areas
north of our County Warning Area.
Aviation...as of 5:00 PM PDT Wednesday...VFR conditions will
persist through late tonight with high clouds streaming
across the region. A frontal boundary is forecast to approach the
North Bay tonight and should help increase the amount of low level
cloud cover...especially over the San Francisco Bay area
northward. Light rain or drizzle will be possible over ksts...yet
confidence remains low and have left precipitation out of the taf
for now. Low clouds that do develop over the region will be slow
to burn-off Thursday morning. Further south...confidence is lower
on the return of stratus over the terminals as boundary layer
moisture will be slower to return.
Vicinity of ksfo...VFR conditions will continue through this
evening. Low clouds expected to return late tonight. Moderate
winds will ease overnight. Moderate confidence.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR conditions will continue
through this evening. Low clouds expected to return after midnight.
Moderate winds will ease overnight. Moderate confidence.
Marine...as of 2:41 PM PDT Wednesday...generally light northwest winds
will persist across the coastal waters through Friday...with
moderate wind speeds off the Big Sur coast. Wind speeds will then
increase and become southerly Friday night into Saturday ahead of
an approaching cold front that will also bring chances of rain to
the region. Northwest swell will slowly diminish through Friday
then increase over the weekend.
... Pinos to pt Piedras Blancas 0-10 nm
Public forecast: blier
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