Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 291236
Area Forecast Discussion
National Weather Service San Francisco Bay Area
536 AM PDT THU SEP 29 2016
...LIGHT RAIN RETURNS FOR NORTHERN PARTS OF OUR AREA STARTING ON
.SYNOPSIS...Cooling trend will continue into the weekend as the
marine layer and onshore flow become better established with a
trough along the West Coast. In addition, a dry cold front will go
through on Friday which will lead to breezy conditions. A system
will drop down from the north over the weekend which will bring
rain to our area especially over the North Bay.
.DISCUSSION...as of 3:20 AM PDT Thursday...After multiple days of
being very compressed, the marine layer deepened throughout
yesterday. Satellite nicely correlates to the 1500 foot level that
the Fort Ord profiler indicates. Surface gradients are also
running nearly 3 MB from the west with just 1 from the north.
Synoptically heights will be on the decrease as an upper level low
associated with a longwave trough currently along the BC coastline
will continue to progress to the south through the day. Highs will
be in the 60s to lower 70s at the coast with mid 70s to mid 80s
inland. In many cases it will be 3 to 6 degrees cooler compared to
On Friday temperatures will continue to cool as the upper level
low progresses down the coast. Ahead of it a dry cold front will
go through which will lead to gusty west to northwest winds with
local gusts to over 30 mph. Behind the front even cooler air will
filter in on Saturday. Highs that day will be mostly limited to a
range of 60 to 75.
Sunday is shaping up to bring us our first round of rain in quite
some time as the trough progresses into California with an
associated upper level low. Rainfall will spread into the North
Bay by the morning and into the San Francisco Bay by the
afternoon. The rain will continue to move southward and possibly
move into Monterey Bay that afternoon or evening. At the same
time, the atmosphere is forecast to become more unstable and due
to the strength of the cold front, a slight chance of
thunderstorms was added to the forecast for the North Bay.
Although there remains good agreement between the models that the
North Bay will pick up rainfall (likely more than 0.20") along
with SF Bay (around 0.10"), models do diverge on how far south the
rain will progress along with the amounts. Canadian solution
remains the most bullish with both coverage and amounts while
ECMWF/GFS operational and ensembles tend to keep the rain focused
north of San Francisco. Current forecast is a bit of a compromise
between the solutions. A few post-frontal showers are expected
A ridge of high pressure will rebuild into our region going into
the middle of next week with another round of rain possible by
.AVIATION...As of 4:45 AM PDT Thursday...Satellite imagery reveals
abundant low clouds across area bays and valleys. The marine
layer currently stand around 1600 feet and is expected to continue
deepening through the day as a low pressure system approaches. Low
clouds will scatter out around 18z this morning. Light winds will
increase slightly this afternoon with the onset of the seabreeze.
Vicinity of KSFO...MVFR cigs has filled in across the bay.
Clearing is anticipated around 19z this morning. Light west winds
will pick up this afternoon with the onset of the seabreeze.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...LIFR/IFR cigs are anticipated to clear
between 18z-19z today. Light winds.
.FIRE WEATHER...As of 5:45 AM PDT Thursday...Marine layer will
continue to deep over the Bay Area the next few days leading to
better recoveries and cooler temperatures. The most notable
weather concern will be increasing winds on Friday afternoon with
local gusts of 20 to 30 mph expected as a dry cold front goes
across. A second system will bring some light rain to our region
especially north of San Francisco.
.MARINE...as of 05:32 AM PDT Thursday...A weakening surface high
pressure area over the eastern pacific will result in lighter
winds across the coastal waters today. winds will strengthen
friday afternoon as an upper level trough deepens off the west
.Tday...SCA...SF Bay from 3 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 PM
PUBLIC FORECAST: Bell
FIRE WEATHER: Bell/MM
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