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

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FXUS66 KMTR 220123

Area Forecast Discussion
National Weather Service San Francisco Bay Area
623 PM PDT Sat Oct 21 2017

.SYNOPSIS...The slight warming trend that got underway across region
today will continue through the first part of the upcoming workweek
as temperatures warm well above seasonal averages on Monday and
Tuesday. Dry weather conditions are also likely to persist with a
slight cooling trend possible late next week.

&& of 01:01 PM PDT Saturday...Temperatures are
slightly warmer compared to this time yesterday under mostly sunny
conditions as high pressure builds in from the south. There is
the potential for some low clouds to redevelop overnight near the
coast and spread locally inland into the Sonoma Valley and around
the San Francisco Bay that will persist through Sunday morning.
Otherwise, look for the warming trend to resume by Sunday
afternoon with most locations warming into the lower 70s at the
coast to upper 70s inland.

The ridge of high pressure will then strengthen and build further
north over the region and result in a warming, drying air mass aloft
early in the upcoming workweek. With this, expecting afternoon
temperatures to warm into the upper 70s to lower 80s even at the
coast with widespread 80s and even a few lower 90s for inland areas
on Monday. Tuesday currently appears to be the warmest with
temperatures in the 80s at the coast to lower 90s inland. A few of
the warmest inland areas may even warm into the middle 90s as weak
offshore flow develops. With that said, overnight conditions will
cool into the 50s during the overnight/early morning hours early
next week to provide relief from the daytime heat. The exception
will be in the hills where overnight lows may only cool into the

A mid/upper level trough is then forecast to drop southward into the
Great Basin and Central Plains by Wednesday which will push the
ridge of high pressure back out over the eastern Pacific. This
should allow conditions to cool slightly Wednesday and through late
week. However, the extended forecast continues to call for above
average temperatures to persist along with ongoing dry weather


.AVIATION...As of 6:23 PM PDT Saturday...Visible imagery shows
coastal low clouds overlapping Mendocino county and partly over
northern Sonoma county. The coastal water`s surface winds gently
veer to the NW direction tonight which should help keep these clouds
located mainly over the coastal waters and immediate coastline
tonight and Sunday morning. Elsewhere it`s VFR based on satellite
imagery and metar observations.

For the 00z tafs forecast confidence is moderate to high VFR will
continue for most of the Bay Area and north Central Coast tonight
and Sunday. Decent radiative cooling late tonight and early Sunday
morning may produce a patch or two of valley fog. Otherwise it`s
VFR under a strengthening (very strong for late October) ridge
Sunday through Tuesday. The ACV-SFO pressure gradient nears 5 mb
late Sunday into Monday and the WMC-SFO gradient increases to 10-13
mb Sunday night into Monday.

WRF model output shows gusty NE winds 30-35 knots over the North Bay
and East Bay hills/mtns extending southwestward to the Santa Cruz
Mountains Sunday night and Monday morning; dry relative humidity in
a deep layer of the atmosphere, longer night-time hours and radiative
cooling supports surface winds decoupling from gusty winds aloft thus
low level wind shear (LLWS) becomes likely from later Sunday into
Monday morning for the terminals KOAK over to KSJC. Will look into
adding LLWS in the 06z taf cycle.

Vicinity of KSFO...Moderate to high confidence VFR. Westerly wind 10-15
knots this evening becoming light late tonight and W-NW upwards to 15-20
knots Sunday afternoon and evening.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Westerly winds gradually subsiding this
evening and becoming light/variable late evening possibly light SE
by Sunday morning. Onshore winds gusts to near 20 knots are possible
Sunday afternoon.


.FIRE WEATHER...As of 5:30 AM PDT Saturday...Gradual warming
trend starts today with light northerly winds. This trend
continues into tomorrow with winds turning more to the northeast
with continued warming and drying. Another round of gusty offshore
winds is forecast for the Napa hills Sunday night into Monday
morning. Recent rain has helped but will need to watch the Sunday
night into Monday morning wind event closely. Long range trends
suggest warm to hot afternoons and very dry conditions with
periods of offshore winds for much of next week.

There is also concern about a potential northerly wind event for
the North and East Bay Hills late Thursday into Friday.

&& of 5:07 PM PDT Saturday...Light split flow over the
waters through the afternoon with increasing northwesterly flow
tonight and into Sunday. A long period northwest swell will
continue to taper down through the day. Hazardous conditions from
squared seas will exist in most offshore areas through tonight.


     .Tngt...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm




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