Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1007 PM PDT Tue Oct 25 2016
Synopsis...a few isolated showers will remain possible over the
North Bay through late tonight with dry weather likely region-
wide on Wednesday. Our next weather system will bring widespread
rainfall,locally heavy at times, to just about all on Thursday as
an upper level low approaches the central coast. Showers will
linger on Friday with yet another storm system set to impact the
region from Saturday afternoon into Sunday.
Discussion...as of 8:55 PM PDT Tuesday...rain appears to have
come to an end over the North Bay this evening with the Santa
Rosa ASOS and the Venado no longer reporting rain. That being
said isolated showers will remain possible through late tonight.
Spotter report from the North Bay earlier this evening confirm a
steady light rain across that region through most of the day
today. Even though Doppler radar didn't pick up on much over the
North Bay ground truth observations picked up 1" of rain over
Venado over the last 6 hours alone. Venado was our wettest spot
today with all other locations coming in significantly drier with
accumulations of a few hundredths to a few tenths during the same
time period. Rain chances will quickly diminish overnight with dry
conditions expected across the forecast area Wednesday.
The forecast remains on track to bring in a significantly wetter
system Thursday. This system is progged to bring widespread
precipitation to the region with period of heavy rain expected
especially over the san cruz and Santa Lucia mountains as the
system takes aim at the central coast. Latest model guidance
depicts precipitable water values in the 1.50" to 1.70" range.
Values vary by model however they do tend to agree that the
deepest moisture advection will be south of the Monterey Bay.
Rainfall totals are expected to range from 0.50" to 1.50" for
most locations with 2.00" to 3.00" expected over elevated coastal
terrain such as the Santa Lucia and Santa Cruz Mountains.
Thunderstorms cannot be ruled out at this point but model
solutions differ with respect the the timing of when the upper
level low will pass overhead. Will add thunderstorms to the mix
if warranted with future model runs.
From previous discussion...as the aforementioned mid/upper level
low shifts inland, widespread rainfall will tapper off Thursday
night into Friday with only lingering showers/rain possible on
Friday. Precipitation amounts will likely be on the low side from
Friday night into Saturday ahead of yet another mid/upper level
system. As this storm system pushes inland to our north, a frontal
boundary will push southward across the region Saturday afternoon
into Sunday morning. With that said, confidence remains lower on
timing of the system and rainfall amounts. Then, lingering
precipitation will be possible through Sunday and potentially into
An active, unsettled weather pattern looks likely to persist heading
into next week as well with temperatures near or below seasonal
averages. If you have any plans late in the forecast period, be
sure to stay tuned for the latest updates.
Aviation...as of 10:07 PM PDT Tuesday...areas of MVFR cigs.
Plenty of moisture lingers over the area, may see patchy fog
developing reducing visibilities to IFR-LIFR. A subtle increase in
wind Wednesday should provide sufficient mixing for MVFR/VFR over
most if not all of the area by afternoon.
Vicinity of ksfo...moderate-high confidence VFR continues this
evening, tempo MVFR cig 06z-10z to prevailing MVFR cig through
Wednesday morning. Low clouds scatter out by late morning or early
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...winds light southeast with VFR persisting thus
far. There could be a few patches of fog around the area early
Wednesday morning. MVFR/VFR returns later Wednesday morning and
Marine...as of 8:12 PM PDT Tuesday...gusty southerly winds will
persist over mainly the northern coastal waters tonight...then
decrease on Wednesday. Another low pressure system is expected to
impact the coastal waters Thursday and into the weekend.
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...rough bar advisory for sf bar until 3 am
Public forecast: CW
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