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

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FXUS66 KMTR 230441
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
841 PM PST Mon Jan 22 2018

.SYNOPSIS...Anticipate partly cloudy skies tonight with patchy
fog developing in the valleys. Dry and seasonably cool weather
forecast Tuesday. Next front arrives Weds morning or midday in the
North Bay and then spreads rain southward later Weds afternoon
into Weds night for the Bay Area into the Central Coast. Steady
rain quickly turns to showers before sunrise Thursday. A round of
more organized showers is possible Thursday afternoon as the upper
low moves inland. Dry weather forecast Friday through the weekend
and into early next week.

&&

.DISCUSSION...as of 8:41 PM PST Monday...Showers across the
southern portion of the forecast area have dissipated however
abundant low level moisture persist. Satellite imagery reveals
cloudy conditions across the North and East Bay to patchy clouds
anchored over the hill south of the Bay Area. The main concern for
tonight remains the possibility of fog development due to the
moist boundary layer and a strengthening inversion as result of a
building area of high pressure over the region.

Tuesday will bring a return of mild and dry weather after the morning
fog burns off. High clouds are anticipated to increase as the next
storm system approaches from the northwest. The forecast remains
on track...no updates expected.


From previous discussion...Run of the mill Pacific frontal
passage on tap for Weds. As has been the trend of late, the models
seem to be showing a less robust frontal passage. Latest timing
would bring steady frontal rains into the North Bay later Weds
morning or around midday. Front will then slide southward through
the Bay Area Weds afternoon and evening. Similar to todays front,
the rain will weaken and become more disorganized by the time it
reaches the Central Coast. The North Bay Coastal hills will be the
winners once again with 1-2 inches of rain possible while amounts
will drop off sharply over the Bay Area and Central Coast. Winds
associated with the front will be fairly light too, some gusts in
the 25-35 mph range as the front passes through.

Any steady rain will quickly turn to showers before sunrise
Thursday. Cold air aloft and an associated shortwave are forecast
to pass through on Thursday afternoon. This should produce an
organized area of rain and isolated thunderstorms, especially
focused from about the Santa Cruz mtns northward. Some brief heavy
rain and small hail will be possible as this feature passes
through.

Dry weather returns Thursday night into Friday. Latest model
trends show above average confidence for dry conditions Friday
through the weekend and into early next week. Some of the gfs
solutions keep the storm track just to our north but ensembles
suggest another West coast ridge could become entrenched so the
Wed-Thu rain may be the last significant rainfall for awhile.

&&

.AVIATION...as of 4:30 PM PST Monday...A weak front is now south
of the MRY Bay Area. Cigs have started to break out except in the
MRY Bay Area but abundant moisture remains over the area behind
the front. Therefore expect MVFR cigs to redevelop in the SFO Bay
Area by around midnight. With light northeast flow expected later
tonight this could bring some fog from the inland valley into SFO
OAK and the approach. Areas of dense fog is expected in the North
Bay Valleys while vsbys could drop as low as 1-3 miles in the SFO
Bay Area between 12Z and 17Z.

Vicinity of KSFO...MVFR cigs expected to redevelop after 08Z.
Vsbys may drop down to 1-3 miles between 12Z and 17Z. West winds
to 10 kts becoming light northeast after 08Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs will be breaking up in the next
hour and there will be a brief period of VFR. However MVFR cigs
are expected to return after 05-06Z due to abundant low-level
moisture.

&&

.MARINE...as of 2:31 PM PST Monday...Switch to northwesterly
winds is progressing down the coast behind the dissipating cold
front, now located along the northern Big Sur coast. Small Craft
Advisories remain in place due to hazardous sea conditions caused
by large swells. These swells will continue to gradually decrease
through Tuesday. However, the next frontal system is set to arrive
mid-week bringing back strengthening southerly winds and
increasing northwest swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...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
             SCA...Rough Bar Advisory for SF Bar

&&

$$

PUBLIC FORECAST: CW
AVIATION: W Pi
MARINE: Blier

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