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

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FXUS66 KMTR 202143
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
143 PM PST Mon Nov 20 2017

.SYNOPSIS...A weather system will bring periods of light rain to
the North Bay and possibly San Francisco today. High pressure will
bring dry and warmer weather to the area Tuesday through Thursday.
The next chance of rain will be late this weekend.

&&

.DISCUSSION...as of 01:41 PM PST Monday...Bay Area radars
continue to show a few showers over the North Bay, but coverage is
a lot less than this morning. Rainfall totals over the last 12
hours range from a few hundredths to three-quarters of an inch.
Precip was mainly confined to north of the Golden Gate, but a few
gages south did tip a little bit. The highest rainfall total did
occur in Sonoma County with two gages near 0.80 inches.

For this afternoon/evening...expect lingering shower activity to
diminish across the North Bay and end by early tonight.
Synoptically speaking, an upper level trough will deepen over the
Eastern Pacific allowing for a ridge of high pressure to build
across California. The ridging will shift rain chances northward
to far NorCal/OR. More notably, the building ridge will bring a
general warming trend to the Bay Area as 850mb temps climb 18-20C.
Based on KOAK sounding climatology, if verified, those temps at
850mb would be exceeding the 90 percentile. At the surface that
translates to highs roughly 10-15 degrees above normal, a little
less around SF Bay and possibly up to 20 degrees above normal over
southern Monterey/San Benito Counties. Highs Tuesday and
Wednesday are forecast to be upper 60s to mid 70s and possibly mid
80s across interior Monterey/San Benito.

By Thanksgiving the ridge flattens a little and begins to shift
eastward. The weakening ridge will allow for slightly cooler
temperatures and about a 15-20% chc for precip across the North
Bay as a cold front approaches. Models have been trending drier
during this time period and tend to keep precip confined to north
of the Golden Gate. Medium range models continue to struggle with
a unified solution for Friday and into weekend. One thing that
they show is a slight chance for showers for the far northern
areas of the North Bay, but differing details. Either way,
rainfall amounts will be minimal at best Friday and into the
weekend.

&&

.AVIATION...As of 9:42 AM PST Monday...For 18z Tafs. CIGs remain
VFR at all TAF terminals but KSTS, where MVFR CIGs prevail. A few
rain showers are possible through the day today at KSTS. Expect
MVFR CIGs to continue through at least 00z, with intermittent VFR
possible. Elsewhere, CIG heights are expected to remain above
3000 feet. Light southeast winds through the day, should stay
below 10 knots. Kept LLWS at KSTS through 20z.

Moderate confidence.

Vicinity of KSFO...Light SE winds will prevail, along with VFR.
Forecast still calls for dry runways. Could be some low
clouds/reduced VIS before sunrise Tuesday, though not very
confidence with that occuring.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Salinas Valley continues to be the area
where SE winds are the strongest this morning. Expect winds to
decrease this afternoon, once the winds switch out of the WNW.
Light winds expected at KMRY. VFR expected through the forecast
period.

&&

.MARINE...as of 09:22 AM PST Monday...High pressure to the south
will keep a very moist sub-tropical flow just north of the
Coastal Waters. Winds are expected to stay light to moderate out
of the south today, with the highest wind speeds remaining over
the northern Coastal Waters. By late week into early next week a
cold front will move southeastward over the coastal waters. Seas
are expected to remain light to moderate through the first part of
next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...None.

$$

PUBLIC FORECAST: MM
AVIATION: BAM
MARINE: BAM

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