Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 280054

Area Forecast Discussion
National Weather Service San Francisco Bay Area
554 PM PDT SAT AUG 27 2016

.SYNOPSIS...Temperatures will remain near to slightly below
seasonal averages through early next week before further cooling
by midweek as an upper level trough pushes inland to our north.
This pattern will change little through late next week with
continue below average temperatures and widespread night/morning
low clouds.

&& of 01:52 PM PDT Saturday...The overall weather
pattern across the region will change very little through tonight.
This should give way to another night of low clouds spreading well
inland into most valley locations as the marine layer generally
remains above 2,500 feet in depth. With this, expecting a mostly
uniform cloud deck with very little in the way of fog development
over inland areas.

While high pressure builds slightly toward the southern and central
California coast from the southwest on Sunday, little change is
anticipated in regards to temperatures. Overall, temperatures will
remain near to slightly below seasonal averages, especially inland.
As the high pressure builds aloft, may see the marine layer compress
some during the day Sunday and into Monday morning. Again, this
should result in very little change in our weather conditions
through early next week.

Inland temperatures will trend downward on Tuesday and through
midweek as a mid/upper level trough pushes into northern
California. The forecast models (especially the GFS) show a slight
chance of precipitation over northern California as the system
pushes inland on Tuesday. However, moisture will be limited across
our region and chances for any measurable rainfall over the North
Bay appears low at this time. Thus, will hold off on adding a
mention into the forecast for now. However, will be worth keeping
an eye on in the coming days.

The larger scale trough over the West Coast will deepen slightly
Wednesday into Thursday and will keep temperatures below seasonal
averages through at least late next week. With this, do expected a
continued marine influence across the region with late night and
morning low clouds spreading well inland before giving way to mostly
sunny skies during the afternoon hours.

&& of 5:54 PM PDT Saturday...Sub-tropical ridge over
the eastern Pacific tilts eastward across CA/NV through early next
week. Area-wide lower level warming is forecast near the 925 mb
level through late Sunday night likely causing the marine
inversion to steadily compress. Minor lower level cooling possibly
returns near the marine inversion Monday; compression of marine
layer depth would then halt on Monday. Present 2.6 mb SFO-SAC
onshore gradient is in-line with the latest NAM run. 00z terminals
are based on continued onshore wind and the marine inversion
becoming shallower with time. MVFR cigs with areas IFR developing
tonight, IFR lifting by late Sunday morning.

Vicinity of KSFO...Low to moderate confidence VFR persists this
evening. The marine layer is plenty deep for evening stratus
intrusion, however onshore winds are on the light side. Pressure
gradient between Half Moon Bay buoy and KSFO is weak-moderate at 1
mb. Would have higher forecast confidence in evening VFR if the
ACV-SFO gradient was stronger, however it`s only 2.1 mb at the
moment and forecast to weaken tonight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Lots of erosion of the coastal stratus
seen on visible imagery as diurnal mixing and sea-breeze circulations
peak and entrainment of drier air reaches back into the marine
layer across the inner coastal waters. Onset of night-time cooling
and decreasing sea-breezes typically closes this clear sky gap
this time of year with stratus and fog filling back in over coastal
areas. Tempo MVFR cigs forecast 03z-07z, IFR cigs forecast tonight.
Clearing likely returning by late Sunday morning.

&& of 01:52 PM PDT Saturday...Light wind and seas will
continue through the remainder of the weekend. Northwest winds
increase early into next week. A mixed short period northwest
swell and a smaller long period southerly swell will continue to
move through the coastal waters.





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