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Area Forecast Discussion
National Weather Service San Francisco Bay Area
1101 AM PDT SUN AUG 28 2016

.SYNOPSIS...Slight warming is forecast for inland areas over the
next couple of days, particularly the North and East Bay Valleys.
Otherwise, little change is forecast through the week ahead and
into next weekend, with continue near normal to slightly below
normal temperatures expected. A relatively deep marine layer will
continue to result in widespread night and morning low clouds. 


.DISCUSSION...As of 9:10 AM PDT Sunday... A short lived ridge
will reign over the realm today ahead of an approaching low
pressure trough to the north. The ridge has compressed the marine
layer and weakened the marine wind field this morning and will
result in slightly warmer and drier conditions today, especially

Further offshore, a few lightning strikes have been detected in an
area of interest between the base of the ridge off of Baja
California and a cutoff low centered around 35N 140W. Remnant
tropical moisture advecting northeastward between these two
features is interacting with the cut off lows energy/dynamics and
resulting in convection over the ocean. This region of interest is
expected to be caught up in the approaching broader trough now
over the Gulf of Alaska and rotate into the region late
Monday/Tuesday. This could bring the slightest of potentials of
dry lightning to the region if convection should continue as the
energy and moisture shift onshore. For now, models indicate this
slight potential primarily over the extreme North Bay, but the
trajectory could drift in any direction in the coming days. That
said, nearly all but a few select areas in the forecast area will
fall outside of any chance of elevated thunderstorms with this

The aforementioned upper trough will be sufficient in mixing out
the marine layer by Tuesday... resulting in a relatively rare
stratus free morning for portions of the coast. The marine layer
is expected to then redevelop and deepen by later in the week as
mean weak troughing returns to the west coast. 

.PREVIOUS DISCUSSION...As of 3:40 AM PDT Sunday...An upper level
high pressure centered off the coast of the Baja Peninsula is
forecast to build gradually north and east and across southern and
central California over the next 24 hours. This is expected to
result in a compression of the marine layer and thus warming for
most inland areas. In addition, light southerly winds near the
coast will transition to westerly by late today and then northwest
on Monday. This will create further warming potential for some
inland areas, particularly the North and East Bay Valleys. Even
with the anticipated warming over the next couple of days, most
areas will only see temperatures return to about seasonal

Early morning water vapor satellite imagery shows an upper low
well offshore, centered out near 35N/142W. Moisture from a
tropical storm to the south of this low (T.S. Madeline) is being
drawn north and east by the cyclonic circulation around the low.
The upper low is forecast to be absorbed into a deepening longwave
trough over the Gulf of Alaska and then ejected eastward as an
open wave towards the northern California coast by Monday Night.
The ECMWF has consistently maintained dry conditions across our
entire area as this system moves inland to our north. But at
various times both the NAM and GFS have indicated at least a
potential for showers/thunderstorms in the North Bay late Monday
Night and Tuesday morning. However, the 00Z NCEP models showed a
trend towards decreased convective precipitation potential. So the
decision was made to leave any mention of showers/thunderstorms
out of the forecast, at least for now. Will need to continue to
monitor this closely since any convection that might develop would
likely produce very little or no rain at the surface and thus
could potentially result in dry lightning.

The models agree in keeping a longwave trough anchored near the
West Coast for the remainder of the week and on into next weekend.
This will mean continued mild temperatures inland. Indications are
there could be sufficient low level mixing to clear low clouds by
late Tuesday, even for areas near the coast. 

&& of 11:00 AM PDT Sunday...Stratus is starting to
clear back to the coast at this time. Look for VFR today with low
clouds returning late.

Vicinity of KSFO...VFR. Afternoon sea breeze winds 16 to 22 knots.
MVFR/IFR cigs after 10Z. 

SFO Bridge Approach...Same as KSFO.

Monterey Bay Terminals...Clouds are expected to clear by 19Z.
Expect low clouds to return by 06Z.

&& of 8:33 AM PDT Sunday...High pressure will
strengthen off the Central and Southern California coast Monday
through Wednesday. Winds will be light west to northwesterly then
northwest winds will increase by Monday. A mixed short period
northwest swell and long period southerly swell will continue to
move through the coastal waters through Monday.


     .Tday...SCA...SF Bay from 3 PM




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