FXUS66 KMTR 191145

Area Forecast Discussion
National Weather Service San Francisco Bay Area
445 AM PDT Sat Aug 19 2017

.SYNOPSIS...a few degrees of cooling are expected over the
weekend and into early next week as an approaching trough of low
pressure weakens the area of high pressure currently over the
Eastern Pacific. Coastal areas will see little in the way of
change with continue night and morning low clouds and patchy fog.


.DISCUSSION...as of 3:05 AM PDT Saturday...Widespread low cloud
will encompass area across the forecast area located below the
1500 ft inversion currently in place. Satellite imagery reveals
stratus from Cloverdale in northern Sonoma to as far south as
Bradley in southern Monterey County. Low clouds are anticipated to
clear to the coast by noon followed by mostly sunny skies across
the interior through the remainder of the day.

Temperatures will cool a few degrees inland this afternoon
compared to Friday as an upper level low forms over Point
Conception resulting in a steep decline in 500mb Height and 850mb
Temperature values. Little if any change is expected along the
coast where low clouds will help moderate the temperature.
Anticipate 60s along the coast, 70s around the bay and 80s and 90s
inland. Temperatures will continue to cool a few degrees per day
on Sunday and Monday. The upper low will remain centered over
Point Conception through Tuesday before gradually weakening and
shifting to the north and east. Temperatures are forecast to
flattening out on Tuesday with very little change expected through
the remainder of the week.

From previous discussion...For Monday morning`s solar eclipse...
If conditions permit, the partial solar eclipse can be viewed
throughout California. Right now, models are all in good agreement
that the upper level low will remain parked near Point Conception
in southern California. For us along the Central Coast and north
to the San Francisco Bay Area, this yields a few outcomes. For
one, the low can help mix out the marine layer, resulting in
mostly clear conditions. On the other hand, the upper low could
help to enhance the marine layer depth. We`ll know a little bit
more over the weekend and will continue to monitor the marine
layer`s response to the trough. Climatologically, the best
locations in the Bay Area for clear skies on a mid/late August
morning would be interior areas of the East Bay away from the
coast, as well as the higher elevations in the Santa Cruz
Mountains, North Bay Mountains, and Diablo Range. The eclipse of
the sun will begin shortly after 9:00 am PDT for the Bay Area with
peak obscuration happening around 10:15 am PDT. Peak obscuration
of the sun will range from 71 percent in Monterey and up to 78
percent in Santa Rosa.


.AVIATION...As of 4:45 AM PDT Saturday...Despite the weaker
onshore gradient this morning, stratus has surged inland
overnight, bringing widespread IFR to MVFR cigs throughout all but
KSJC this morning. This comes as the marine layer has deepened to
2000 feet and showing a more uniform texture and distribution on
satellite imagery. As a result, stratus this morning likely will
stick around longer than yesterday morning, with sites generally
mixing out between 17-19Z depending on location. Breezy onshore
winds will occasionally become gusty by the afternoon. For
tonight, look for a repeat of last night as marine layer depth and
onshore gradients should be similar.

Vicinity of KSFO...Borderline MVFR/IFR through 16-17Z. Breezy to
gusty afternoon winds. Similar marine layer timing and cigs for

SFO Bridge Approach...Similar to SFO except clearing earlier.
Satellite imagery shows a hole in the stratus over the South Bay
where winds are upvalley rather than onshore.

Monterey Bay Terminals...LIFR to IFR cigs through as late as 20Z.
Brief afternoon clearing will precede an early return of stratus
by early this evening.


.MARINE...as of 2:52 AM PDT Saturday...Moderate, occasionally
gusty, northwest winds will prevail across the waters through
tonight as high pressure builds in from the west. Locally steep
wind waves will also accompany increasing winds.


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay from 9 AM




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NWS MTR Office Area Forecast Discussion