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

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FXUS66 KMTR 280216

Area Forecast Discussion
National Weather Service San Francisco CA
716 PM PDT Mon May 27 2024

...New UPDATE...

Issued at 131 AM PDT Mon May 27 2024

Warmer today as a warming trend continues through the week.
Afternoon highs slightly above normal on tap for next weekend.


Issued at 715 PM PDT Mon May 27 2024

Inland areas were generally at seasonal averages this afternoon
while coastal locations were up to 9 degrees below normal for this
time of year. This was thanks to a marine layer at around 1,800-
2,000 feet in depth that refused to mix out. The warming trend will
take a pause for tomorrow and will see similar temperatures as we
did today once low clouds retreat to the coast. Low clouds are
forecast to return tonight and spread locally inland across the
Central Coast, around the San Francisco Bay Area, and places such as
Napa. The ongoing forecast remains on track with no updates needed
at this time.


Issued at 123 PM PDT Mon May 27 2024
(This evening through Tuesday)

Interesting current weather situation around the Bay Area and
Central Coast. It`s all about the details. Generally speaking,
morning marine layer was slow to clear back to the coast and for
the coast clouds never cleared. As for the details, moderate
onshore flow (SFO-SAC) and falling 500 mb heights likely
contributed to the slow clearing of morning clouds. If one were to
overlay the morning layer footprint and 24 hour trends one would
see cooler temps today where the marine layer had some influence.
Areas outside of the marine layer footprint are running a little
warmer than yesterday.

Heading into Tuesday - the marine layer lurking along the coast
will move inland again so no drastic change with overall sensible
weather from the last few nights. One change will be the longwave
pattern overhead. The ridge the brought our recent warmup will
flatten as a broad upper level trough sweeps through the PacNW.
The flattening ridge will keep the marine layer established with
overall cooling temperatures, still below seasonal averages.


Issued at 140 PM PDT Mon May 27 2024 (Tuesday night through next

The cooling trend will be short-lived as the flattened ridge
begins to build back over the region with warming 850 mb temps and
rising 500 mb heights. Still looks like night/morning clouds with
inland afternoon sunshine will persist. The warming trend will
continue into next weekend. Far inland locations will reach the
low 90s by week`s end. The interior warmth on Friday will lead to
moderate HeatRisk.


(00Z TAFS)
Issued at 551 PM PDT Mon May 27 2024

Marine layer stratus is persisting from Point Reyes and San Francisco
to the southern Monterey Bay with patches of stratus also along
the Big Sur coast. The marine layer depth varies from 1300 feet at
Bodega Bay to 2000 feet at Fort Ord. The 3.9 mb SFO-SAC pressure
gradient (onshore wind) prevails compared to 3.4 mb ACV-SFO, 1.1 mb
SMX-SFO gradients. A surface high pressure ridge over the north
Central Coast has steepened the SNS-SJC pressure gradient to 2.8 mb,
and with an eddy circulation forecast to develop over southern
Santa Cruz County this evening, a wind shift to southeast is forecast
to reach KSJC Airport later tonight (the wind may transport a stratus
ceiling from vicinity Hollister to the Santa Clara Valley).

Lower level temperature advection is forecast to vary only minimally
overnight therefore the marine layer temperature inversion and
marine layer depth should stay approximately the same overnight and
Tuesday morning. Ceilings will be a mix of MVFR and IFR in stratus
overnight, stratus mixing out by late Tuesday morning or early
afternoon, otherwise VFR Tuesday.

Will need to closely monitor the SFO-SAC pressure gradient Tuesday,
the 18z NAM is forecasting 4 to 5 millibars (mb) of onshore
pressure gradient (gusty winds) Tuesday afternoon and evening.
Statistical guidance shows gusty west winds developing KOAK and
KSFO. Otherwise it`s a low confidence forecast regarding stratus
coverage this time Tuesday evening, that`s a long time from now to
try to pin down stratus with accuracy.

Vicinity of SFO...Stratus /MVFR ceiling/ is piling up along the
coast on the ocean side of the SF Peninsula, it`s VFR so far at
KSFO, however with a solid westerly wind the transport of stratus
is likely, 24 hour trend at SFO is cooler with the surface
dewpoint temp (measure of water vapor) steady. Tempo stratus
/MVFR/ is forecast this evening 03z-07z then MVFR ceiling
prevailing overnight through 17z Tuesday morning. Low confidence
on 17z mix out Tuesday since the westerly wind is forecast to
steadily increase late morning through afternoon, which may keep a
stratus feed going longer than advertised. Westerly wind gusts to
25 knots this evening, easing overnight then moderate to high
confidence westerly wind gusts reaching the lower 30 knots (it may
near airport weather warning criteria 35 knots or higher) Tuesday
late morning, afternoon and early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus /MVFR ceilings/ held together
all day along the immediate coast, stratus is here for the
overnight. Mainly MVFR this evening with the marine layer depth
near 2000 feet, though later tonight and Tuesday morning there may
be locally IFR ceilings developing with more localized and steady
surface to near surface cool air advection forecast across the
Monterey Bay. MVFR-IFR ceilings mixing out by late Tuesday morning
or early afternoon, though it`s a low confidence forecast,
current HREF output shows stratus lingering nearby along the
Monterey Bay in the afternoon.


(Tonight through next Saturday)
Issued at 442 PM PDT Mon May 27 2024

Breezy to gusty northwest winds continuing across the coastal
waters through the week with westerly breezes increasing each
afternoon and evening across the bays. Wave heights beginning to
increase by the middle of the work week up to 11 to 13 feet.


PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 3 AM Tuesday to 3 AM PDT Wednesday for
     Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory until 3 AM PDT Wednesday for Pigeon Pt to
     Pt Pinos 10-60 NM.




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