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

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FXUS66 KMTR 301200

Area Forecast Discussion
National Weather Service San Francisco Bay Area
500 AM PDT Thu Mar 30 2017

.SYNOPSIS...Cooler and breezy conditions are forecast for
today in the wake of a cold frontal system. Most locations will
not receive measurable rainfall from this dry system. Locally
strong and gusty northwest winds are likely from Thursday
afternoon into Friday. A warming trend is then expected for the
upcoming weekend as high pressure rebuilds over the region.


.DISCUSSION...As of 2:55 AM PDT Thursday...Satellite imagery shows
a weak, dry cold front entering the state over northwest
California preceded by a discontinuous cloud bank early this
morning. The cloud decks ahead of the frontal boundary range from
the lower levels well ahead of the front (with several weather
stations reporting ceilings at 800 feet or lower), up to around
15000 feet further upstream. At this time, no precipitation has
been observed as this system advances into the local region, with
only light precipitation observed further north up the California
coast. Only minimal to trace amounts of precipitation are
expected locally as this systems moves across the area, with all
short term models showing dwindling chances of rain after sunrise.
This system will result in much cooler temperatures today, with
temperatures generally 5 to 10 degrees cooler than yesterday. This
cooling comes from a combination of increased onshore flow, cold air
advection, and decreased insolation from the varying cloud decks.

The NW-SE pressure gradient will tighten in the wake of this
system as it exits into southern California and high pressure
builds off the northern California coast. This will result in
increasing northwest winds in the wake of the aforementioned
system. The strongest winds will occur along the coastline, which
will begin to ramp up later this morning behind the front, then
strengthen later this afternoon into early this evening, before
subsiding tonight. The strongest winds will then shift to the
higher inland terrain later tonight through midday tomorrow. As a
result, a wind advisory is now in effect for the coast through 8pm
tonight, and midday friday for the higher inland terrain. Local
wind gusts up to 45mph are expected by later tomorrow, with gusts
exceeding 50mph possible over the higher inland terrain through
midday tomorrow. Winds will then subside into Saturday, where
locally breezy conditions are expected to persist.

The air mass is expected to dry out into Friday, allowing for peak
diurnal heating, and a rapid warmup through the end of the week as
a ridge of high pressure builds inland. Expect to see temperatures
rise further into Saturday as the ridge shifts inland. The ridge
weakens later into the weekend, leading to near normal seasonal

By early next week, another dry, breezy system for the region
will slide into California from the northwest and descend into the
Great Basin. High pressure then builds into the region through mid
week, bringing warmer, drier conditions. Longer range models show
a deeper storm system well to the northwest late next week,
however, there are vast differences in the trajectory. For now,
this stronger system looks more like a Pacific Northwest event,
however, it is far enough out in the extended period that the
forecast models may cause it to drift southward over the coming
days.  Stay tuned for the latest info!

&& of 04:52 AM PDT Thursday...A mixed bag of IFR and
MVFR Cigs are currently being reported across the district, in
addition to light DZ or RA, mainly at coastal terminals. Low
cigs and DZ should lift and end around 14-15Z for the SF Bay
Area, and closer to 17-18Z for Monterey Bay terminals. The windy
northwest winds will be the biggest aviation concern today, once
cigs lift this morning. Model guidance continues to show NW winds
increasing through the day, becoming gusty later this morning.
Wind gusts may be greater that 30 kt, esp for SF Bay Area
terminals. These winds will continue through the evening, and
psbly through Friday morning. Moderate to high confidence with
cigs; moderate confidence with winds and timing.

Vicinity of KSFO...MVFR/IFR cigs through about 14-15Z. Light DZ/RA
may drop VIS below 3SM, as well. VFR anticipated after 15Z. Strong
and gusty W-NW winds late this morning and through the day. Winds
will be sustained at 15-25 kt, with gusts in excess of 30 kt
likely. An Airport Weather Warning (AWW) for winds at KSFO will
be highly considered later this morning. At this time, confidence
is low on exact timing of wind gusts reaching 35 kt. As of 11Z,
KSFO has been reporting NW wind gusts of 20-28 kt over the past
hour, which suggests AWW needed by mid-late morning. Will update
as needed.

SFO Bridge Approach...Low cigs will likely clear north to south
this morning. KSFO may clear before the SMB. Have the bridge
clearing closer to 15-16Z.

Monterey Bay Terminals...MVFR/IFR cigs/vis through about 17-18Z.
VFR afterwards. Strong and gusty W-NW winds this afternoon and
evening, 15-20 kt, gusting 25-30 kt.

&& of 04:19 AM PDT Thursday...0800z (0100 AM PDT)
surface observations and buoy data depicted a cold front entering
the northern portions of the coastal waters. Northwest winds
behind this cold frontal passage will increase through the day
today. Surface high pressure will build over far northern
California into Friday, resulting in Gale Force winds over the
coastal waters beginning later this afternoon and continuing into
Friday, and possibly later for the outer water zones. Northwest
swell will level off while swell periods steadily decrease today.
Large and very long period northwesterly swell will return to the
coastal waters late Saturday night that will last through the


     .Tday...Wind Advisory...Coastal Areas 12PM THU to 8PM THU.
                             Inland elevated terrain 12AM FRI
                             until 12PM FRI.
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             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
             GLW...Pt Arena to Pt Reyes 0-10 nm from 5 PM
             GLW...Pt Reyes to Pigeon Pt 0-10 nm from 5 PM
             GLW...Pigeon Pt to Pt Pinos 0-10 nm from 5 PM
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm from 5 PM
             GLW...Pt Arena to Pigeon Pt 10-60 nm from 5 PM
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 5 PM
             SCA...Rough Bar Advisory for SF Bar until 3 PM
             SCA...Mry Bay from 2 PM
             SCA...SF Bay from 3 PM




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