NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 232356

Area Forecast Discussion
National Weather Service San Francisco Bay Area
456 PM PDT Wed Aug 23 2017

.SYNOPSIS...Not expecting much change in weather conditions heading
into Thursday as temperatures remain slightly below seasonal
averages with overnight and morning low clouds. A warming trend will
then begin Friday and extended into early next week as high pressure
builds over the region. By Sunday and Monday, very warm to hot
daytime temperatures will be possible across inland areas.

&& of 1:35 PM PDT Wednesday...A weak short-wave
trough and associated low pressure system remains off of the
central and southern California coast today. This has helped to
maintain a modest marine layer of around 1,500 feet in depth.
While low clouds will burn-off over inland areas and mainly
retreat to the coast, stratus will again return to coastal areas
and adjacent valleys overnight with the chance of patchy fog and
drizzle as the marine layer becomes more compressed. Little
overall change is forecast into Thursday afternoon with inland
temperatures remain on the cool side of normal while coastal areas
warm into the 60s and 70s.

The aforementioned trough is forecast to dissolve by Friday as high
pressure over the Desert Southwest builds westward. This will work
to further compress the marine layer and result in less widespread
cloud cover, especially across the inland valleys. In addition,
temperatures aloft will warm and bring about warmer temperatures
across inland areas. As the ridge strengthens aloft, surface
temperatures will continue to warm through the weekend with more
widespread 80s and 90s inland with our warmer locations likely to
exceed the 100 degree mark by Sunday. In addition, overnight lows
will not cool as much, especially in the hills where temperatures
may only cool into the 70s. With this, the threat for heat related
illnesses will increase by Sunday into Monday given the hot daytime
temperatures and limited overnight cooling. Meanwhile, coastal areas
will notice a warming trend yet will continue to benefit from the
cool onshore flow. Will closely monitor the need for any heat
related products heading into late week with regards to the
Sunday/Monday timeframe.

The ridge looks to remain the dominate weather feature heading into
much of next week as well. With that said, the ridge does appear to
weaken slightly and shift a bit more inland by the middle of next
week. With this, do expect the peak heating to occur Sunday into
Monday with a slight cooling trend by the middle of next week.
Temperatures will likely rebound back closer to seasonal averages
along with continued dry weather conditions through the entire
forecast period.


.AVIATION...As of 4:56 PM PDT Wednesday for 00Z TAFs...Widespread
stratus along the coast, an 1800 ft marine layer and an
increasing onshore gradient caused by the inland shift of the
surface trough will result in a return of the low clouds this
evening and overnight across area terminals. Moderate onshore flow
will prevail through this evening then gradually diminish
becoming light overnight.

Vicinity of KSFO...VFR conditions will prevail through this
evening. Borderline MVFR/IFR cigs and vsbys anticipated to return
between 03z-05z tonight. Moderate to occasionally gusty west
winds will continue through this evening then becoming light

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs will lower to IFR between
01z-02z this afternoon. A decrease in vsbys expected around 10z
tonight. Moderate west to southwest winds will ease this evening
then becoming light overnight.

&& of 04:40 PM PDT Wednesday...Northerly winds will
continue to increase through the evening and overnight as high
pressure builds to the west. Expect these winds to persist over
the waters through the end of the week. No  significant long
period swell is forecast through the rest of the week.


     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 9 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 9 PM
             SCA...SF Bay until 9 PM




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NWS MTR Office Area Forecast Discussion