Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
412 PM PST Thursday Nov 20 2014
Synopsis...look for scattered shower to continue at least through
the evening with thunderstorms also possible. Unsettled
conditions will continue through Saturday when
another...potentially stronger system moves across our area
starting Friday evening in the North Bay and then across our
entire area Friday night into Saturday. Dry weather is then
forecast through at least Thanksgiving day.
Discussion...as of 3:00 PM PST Thursday...forecast continues to
be on track this afternoon as the main band of rain is pushing
across our County Warning Area and advancing to the southeast. Radar returns have
not been that impressive, although in the last 30 minutes a
stronger cell did pop up west of Bodega Bay that prompted a marine
weather statement to be issued. For the rest of the afternoon into
the evening the more unstable air (that triggered the cell over
the northern waters plus off the eka coast) will continue to
progress to the south. Decided to increase the mention of thunder
in the grids to most of the northern half of the County Warning Area.
Rainfall amounts so far have ranged from over an inch for parts of
the North Bay mountains to 1/3"-2/3" for a good portion of the sf
Bay region, with lesser amounts to the south. Radar does show a
nice band currently approaching the Monterey coastline, so numbers
down there should nicely increase before the evening is over.
After about a 24 hour break, another Pacific storm system associated
with will move to our area starting Friday evening for the North
Bay, continuing through the sf region Friday night, and down to
Monterey Bay area Saturday morning to early afternoon. Current
rainfall forecast is close to the amounts we are seeing today,
although with precipitable water values forecast to approach 1.5" at the coast,
still looks like there is a possibility of higher values being hit.
Instability does appear to be less with the second storm compared
to today, so at this time thunderstorms are not forecast. Rain
will end by Saturday evening.
Dry weather will return to our area for next week as a ridge of
high pressure returns to our County Warning Area. Temperatures will warm back to
above normal values. Also, Thanksgiving day at this time still
Aviation...as of 4:12 PM PST Thursday...for 00z tafs. Initial
band of precipitation has moved onshore but there are plenty of showers
still over the Bay area with more developing offshore. Winds at
the buoys and terminals are still southeast but should shift by
03-04z. Thunderstorms in the vicinity was kept in Bay area tafs until 03z and given current
radar returns that still seems plausible with most active cells
currently near Point Reyes. Clearing will be gradual overnight and
enough boundary layer moisture left over to expect some MVFR ceilings
to start the day Friday. Medium confidence.
Vicinity of ksfo...another band of showers and possible T-storms
through 03z...after which winds should shift to westerly with
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...-shra through this evening roughly
03-04z. Then light westerly and gradual clearing overnight.
Marine...as of 3:48 PM PST Thursday...northwesterly winds will
return to the coastal waters tonight behind the frontal boundary
that is moving across the region. The chance of rain will continue
through tonight with a slight chance of thunderstorms mainly
through this evening. Southerly winds will develop again Friday as
a stronger system passes to our north before moving southward over
the waters Saturday with rain and increasing winds.
Public forecast: Bell
Visit US at weather.Gov/sanfrancisco
Follow US on facebook, twitter, and youtube at: