Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 290558 RRA
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1038 PM PDT SUN AUG 28 2016
.SYNOPSIS... Fair weather conditions will persist into Monday with
slightly below seasonal temperatures forecast. A low pressure
disturbance will impact the area on Tuesday, bringing breezy
winds, slightly cooler temperatures and a minor possibility of dry
thunderstorms over the north Bay. A mean trough pattern will bring
continued below seasonal temperatures through the end of the week.
.DISCUSSION...as of 07:00 PM PDT Sunday...After mostly sunny
conditions region-wide this afternoon, many inland locations were
a few to as much as 10 degrees warmer (especially in the North Bay
valleys) compared to yesterday as weak ridging built in aloft.
While low clouds completely cleared the coast and remained mostly
offshore this afternoon, do expect low clouds to redevelop tonight
near the coast and spread locally inland given increased boundary
layer moisture and marine layer around 1800 feet in depth. With
that said, do not expect as extensive coverage of clouds as seen
in previous days. Temperatures overnight will fall into the 50s in
most locations with 60s to near 70s in the hills above the marine
layer. Winds will be on the increase tomorrow ahead of an
approaching mid/upper level trough. The ongoing forecast for
tonight remains on track and no updates are anticipated at this
time. Please see the previous forecast discussion below for
.PREV DISCUSSION...As of 2:20 PM PDT Sunday... A 592DM ridge centered
at 30N 125W is tilted over California and reigning over the realm
this afternoon. The ruling ridge has brought warmer temperatures
to inland communities and has also compressed and weakened the
marine layer offshore and along the coast. Most coastal locations
are cloud free this afternoon as the marine layer is pushing away
from the coast and providing for ideal beachfaring conditions.
Upstream of the ridge are a pair of upper low pressure
disturbances. The broader 558DM low is centered over the Gulf of
Alaska, meanwhile, a smaller 576DM low centered around 35N 140W is
present near the base of the broader aforementioned low.
Presently, we are watching a convective area of interest between
the base of the ridge off of Baja California and the cutoff low
at the base of the broader trough. Remnant tropical moisture from
tropical storm Madeline is advecting northeastward between these
two features and interacting with the cut off lows
energy/dynamics, resulting in enhanced 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 early Tuesday. As a result, the North Bay has a
5-10% chance to see dry lightning through early-midday Tuesday as
the energy and moisture shift onshore. As with most fine scale
convection, the trajectory could drift in any direction in the
coming days so the forecast grids reflect a larger than
anticipated area that will be impacted. We are only expecting a
few isolated thunderstorms, if any, to develop, and only a few
isolated locations will likely be impacted. A similar set up in
2008 generated much more convection/lightning than all the
forecast models suggested, so we are taking a cautionary view on
this similar pattern and watching it closely.
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, bringing continued
cooler than seasonal temperatures, a deeper marine layer, and
increased onshore flow.
.AVIATION...as of 10:38 PM PDT Sunday...Marine layer has compressed
to 1,600 feet at the Fort Ord profiler. Stratus and fog making a
return on onshore winds tonight, areas IFR cigs/vsbys forecast late
tonight and Monday morning. 06z terminals reflect a bit gustier winds
Mon afternoon into early Tue morning.
Vicinity of KSFO...VFR tonight then low confidence tempo IFR cig
12z-16z Monday. VFR late Monday morning and afternoon along with
late day gusty westerly winds 20-30 knots.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Areas IFR cigs late tonight and Monday
morning. VFR returns mid-late Monday morning and afternoon. Locally
gusty W-NW winds Monday afternoon and evening.
.MARINE...as of 8:51 PM PDT Sunday...High pressure off the central
and southern California coast will result in increasing northwesterly
winds over the coastal waters Monday through Wednesday. Gusty onshore
winds are predicted for the bays later Monday afternoon into Tuesday.
A mixed short period northwest swell and long period southerly swell
will continue to move through the coastal waters through Monday.
PUBLIC FORECAST: RGass
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