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

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FXUS66 KMTR 240017

Area Forecast Discussion
National Weather Service San Francisco Bay Area
517 PM PDT Tue May 23 2017

.SYNOPSIS...An inland cooling trend will continue through late week
as high pressure weakens and the marine influence increases. Minor
warming is then expected during the upcoming weekend as high
pressure returns to the West Coast.

&& of 01:32 PM PDT Tuesday...Low clouds continue to
hug the coast this afternoon with mostly sunny skies inland. With
this, the warmest temperatures persist over inland areas while
cooler temperatures (generally in the upper 50s to lower 60s) are
common at the coast. This trend will likely persist into tomorrow,
with low clouds spreading inland this evening and into the
overnight hours with a marine layer of around 1500 feet in place.
However, as the ridge aloft weakens and onshore flow increases,
inland locations will see the gradual cooling trend continue into
Wednesday. With the deepening marine layer, cannot rule out patchy
coastal drizzle/mist during the late night and early morning.
However, measurable precipitation is highly unlikely.

Further cooling is expected late in the week as the ridge flattens
and an upper level low drops down into the northern Rockies. With
this and an increase marine influence, looks for temperatures to
fall below seasonal averages for just about all inland locations.
More widespread 60s and 70s will be likely during the afternoon hours
beginning on Thursday and continuing through Saturday.

By late in the weekend and into early next week, a ridge of high
pressure is currently forecast to rebuild over the West Coast. This
would likely result in a slight warming trend with afternoon
temperatures back to near seasonal averages. In addition, look for
mostly sunny afternoon conditions inland while coastal clouds will
be possible.


.AVIATION...As of 5:17 PM PDT Tuesday...The marine layer is
deepening with a decent onshore push of stratus and fog expected
this evening into Wednesday morning. Timing stratus cigs will be
challenging due to a southerly component to the wind over the
inner coastal waters this evening. Additionally a lower level
cyclonic circulation over the offshore waters advances eastward
reaching the coastal waters just west of the Bay Area Wednesday.

Ongoing area-wide surface to lower level cooling thus expected to
couple with a strengthening southerly gradient (SMX-SFO presently
1.7 mb) and a southerly wind component will likely become more of
an influence on the marine layer from later tonight into Wednesday.
Surface pressures will generally be highest over the Central Coast
and lowest over far northern California through Wednesday favoring
a continuation of the SMX-SFO gradient nearing 4 mb tonight and
Wednesday per latest NAM model output.

Vicinity of KSFO...Low to moderate confidence VFR holds this evening
which is highly dependent on wind direction and strength as well as
the marine layer depth; presently San Carlos sodar shows it`s near
1,000 feet deep. As long as the marine layer depth holds and the
wind does not become more due westerly VFR should hold for a while
longer this evening. IFR is forecast, but not til much later tonight
with general trend toward MVFR cig early Wednesday morning. Gusty
W-SW winds likely Wednesday late morning and afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs trending to IFR this evening
the possibly back to MVFR cigs late tonight and Wednesday morning.
Low confidence VFR redevelops by afternoon Wednesday.

&& of 4:42 PM PDT Tuesday...Light winds will to continue
tonight across the waters. Split flow tomorrow expected with
increasing northerly winds over the northern outer waters and
increasing southerly winds along the coast. Winds are forecast to
weaken late this week.


     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
             SCA...SF Bay until 9 PM




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