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

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FXUS66 KMTR 171958
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1258 PM PDT Thu Aug 17 2017

.SYNOPSIS...A gradual warming trend is forecast to continue
through late week as high pressure builds over the region. With
this, overnight and morning clouds can be expected as well,
especially along the coast and nearby valley locations. A cooling
trend is then expected late in the weekend into early next week as
an upper level trough impacts the region.

&&

.DISCUSSION...as of 12:57 PM PDT Thursday...Low clouds across the
region have mostly retreated to the Pacific early this afternoon
with the exception of the North Bay coastline and across the
western portion of San Francisco. Meanwhile, profiler data
continues to show the marine layer holding on strong at around
1,800-2,000 feet in depth. Above the marine inversion, warmer
temperatures are also noted and have translated to warmer
temperatures in the hills and inland valleys. This trend is likely
to persist through late week as a ridge of high pressure builds
in from the eastern Pacific. With the presence of the marine
layer, low clouds will again return to the coast tonight and
spread locally inland into the valleys. Similar to today, these
clouds will burn-off through midmorning and give way to mostly
sunny skies in the afternoon for most locations both on Thursday
and Friday. Overall, temperatures will be near seasonal averages
with 60s to 70s at the coast and 80s to 90s inland.

The aforementioned ridge of high pressure will shift westward out
further into the Pacific this upcoming weekend and be replaced by a
mid/upper level trough. The latest model run of the GFS continues to
maintain near average temperatures on Saturday before showing a
cooling trend spreading inland Sunday. Meanwhile, the NAM and ECMWF
both show the cooling trend to begin on Saturday and spreading
inland into early next week. Regardless, temperatures are forecast
to cool slightly below seasonal averages early next week. The
challenging part of the forecast will be how much this mid/upper
level trough and associated low that is forecast to develop will
impact the marine layer. Depending on the exact set up, the marine
layer may mix out early in the week and result in earlier than
normal burn-off time of low clouds. Overall, dry weather conditions
are also forecast to persist through the middle of next week.

&&

.AVIATION...As of 10:22 AM PDT Thursday for 18Z TAFs. Visible
satellite shows this morning`s stratus continuing to mix out.
Expect the return to VFR conditions at all terminals within the
next hour. The building upper level ridge over the eastern Pacific
will continue to compress the marine layer over the next 24
hours. This will likely lead to lower ceilings for Friday morning
at terminals impacted by stratus.

Vicinity of KSFO...Visible satellite shows this morning`s stratus
quickly mixing out over the terminal as of the 18Z TAF issuance.
VFR conditions expected to prevail through at least the evening
hours. Light west winds will increase this afternoon to around 15
kt. Chance for stratus returns overnight, though the big question
is how the compressed marine layer will become.

SFO Bridge Approach...Few lingering low clouds along the approach
possible until 1800 or 1830Z, otherwise similar to KSFO.

Monterey Bay Terminals...VFR conditions expected to prevail
through this afternoon and early evening with the transition back
to IFR overnight. Can`t rule out ceilings dropping to LIFR levels.

&&

.MARINE...as of 08:43 AM PDT Thursday...Generally light and
variable winds are expected over the coastal waters today. Locally
breezy conditions are possible later this afternoon and evening
near the Golden Gate Gap and Angel Island. Expect increasing
northwest winds beginning late tomorrow and lasting through the
weekend as the ridge strengthens further.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...SF Bay until 9 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Rowe
MARINE: Rowe

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