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

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181
FXUS66 KMTR 191752
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1052 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 08:09 AM PDT Saturday...Non-operational and
experimental GOES-16 visible channels reveal another morning of
stratus for much of the San Francisco Bay Area and central Coast.
The low clouds even managed to reach parts of the inland East Bay
earlier this morning, including Livermore where overcast
conditions were observed from 5 am PDT to the present. Satellite
also depicts the low clouds pushing well into the Salinas Valley
and coming within about 15 miles of the Monterey-San Luis Obispo
county line. Most communities that are blanketed with low clouds
at this time can expect a gradual transition to mostly clear skies
by late morning, though there could be some lingering clouds
along the immediate coastline. An upper level low near Point
Conception will allow for 2 to 4 degrees of cooling compared to
yesterday for interior areas this afternoon as height and
thickness values decrease.

No major updates planned for the forecast package this morning.
Please refer to the previous discussion section for additional
details.

&&

.PREV 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.

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 10:45 AM PDT Saturday...Slow eroding of the
stratus will continue through late morning and into the early
afternoon. All TAF sites are expected to be VFR by 20z. Marine
layer is still holding at around 2000 feet at this hour.
Anticipate MVFR/IFR cigs to return tonight for most sites. Breezy
onshore winds will occasionally become gusty this afternoon.

Vicinity of KSFO...Cigs are starting to lift and scatter out
around the terminal, though still not confident on exact clearing
time. Breezy to gusty afternoon winds, sustained around 15 kt,
with gusts near 20 kt at times. Similar marine layer timing and
cigs for tonight.

SFO Bridge Approach...Clearing over bridge may occur around the
same time as terminal. Confidence is high with clearing slightly
after 18z.

Monterey Bay Terminals...MVFR cigs holding strong over MB
terminals. KSNS should clear by 1830z, though this will be
monitored. Still anticipate KMRY to clear by 20z, but confidence
is still low at this time. Brief afternoon clearing will precede
an early return of stratus by early this evening. Light to
moderate onshore winds this afternoon.

&&

.MARINE...as of 10:31 AM PDT Saturday...Moderate, occasionally
gusty, northwest winds will prevail across the northern outer
waters and the San Francisco Bay through  tonight as high pressure
builds in from the west. Winds decrease for all waters by Sunday
evening. Locally steep wind waves will  also accompany increasing
winds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay

&&

$$

PUBLIC FORECAST: Rowe/CW
AVIATION: BAM
MARINE: BAM/DRP


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