284
FXUS66 KMTR 121814
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1114 AM PDT Wed Aug 12 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 118 AM PDT Wed Aug 12 2026

 - Near-critical fire weather conditions Wednesday afternoon
   through Thursday early morning across Monterey and San Benito
   Counties due to high based thunderstorms

 - Up to a 15% chance for elevated rain showers/thunderstorms
   Wednesday across the Central Coast

 - Cooling trend through Friday will bring well below normal
   temperatures, gradual warming trend through the weekend

 - Minor coastal flooding for bayshore locations along the San Francisco
   Bay, San Pablo Bay, and Monterey Bay through Thursday morning

&&

.SHORT TERM...
Issued at 118 AM PDT Wed Aug 12 2026
(Today and tonight)

Today`s forecast attention turns 300 miles southwest of Point
Conception where a low pressure system is bringing up to a 15%
chance for elevated rain showers/thunderstorms Wednesday across the
Central Coast. This has the potential to be a low probability/high
impact scenario and will bring near-critical fire weather conditions
Wednesday afternoon through Thursday early morning across Monterey
and San Benito Counties. So far, lightning has remained confined to
the circulation with mid-to-high level clouds beginning to stream
in. An upstream upper-level trough, mid-level lapse rates around 7.5
degrees C/km creating sufficient MUCAPE values around 500-1000 J/kg,
and PWATs in excess of one inch are the thunderstorm ingredients.
Confidence is lowest in the lift/trigger as guidance/models are
struggling with the circulation and cutoff lows are notorious to
forecast due to their independence from the jet stream. Uncertainty
lies in what these two features will do when they collide, including
track and potential dry air entrainment which would lower rain
shower/thunderstorm chances. With moisture confined to the mid-to-
upper-levels and a dry slot in the low levels, DCAPE values of 500-
1000 J/kg will be capable of producing erratic/gusty outflow winds
of 35-45 mph with any rain showers/thunderstorms that develop. The
main concern is lightning which will pose the risk for new fire
starts and has the potential to hinder operations on the Timber
Fire. Smoke from the Timber Fire will continue to be transported
into the Central Coast via light southwesterly winds. The smell and
appearance of smoke will be the worst under the inversion at night
and in the morning. Sensible weather wise, the cooling and
moistening trend will continue through Friday with temperatures well
below normal and a deep marine layer bringing a chance of drizzle.
Minor coastal flooding is expected during the highest high tide
(evening/overnight) for bayshore locations along the San Francisco
Bay, San Pablo Bay, and Monterey Bay through Thursday morning.

&&

.LONG TERM...
Issued at 118 AM PDT Wed Aug 12 2026
(Thursday through Tuesday)

Cooling and moistening trend continues through Friday as global
ensemble clusters are in agreement that upper-level troughing will
remain over the West Coast. By the weekend, heights will begin to
rise as upper-level ridging builds in from the Southeast while
simultaneously a cutoff low develops off the Pacific Northwest.
Sensible weather wise, this will result in a gradual warming trend
and an increase in onshore flow; however, temperatures will remain
below normal.

&&

.AVIATION...
(18Z TAFS)
Issued at 1112 AM PDT Wed Aug 12 2026

Another day, another marine layer. Stratus is making its way out of
the remaining terminals and will retreat to the coastline for the
rest of the day. VFR conditions will prevail through the afternoon.
Onshore winds, generally from the southwest, become moderate (10-15
kt) this afternoon across the majority of TAF sites. Winds remain
around 7-10 kt overnight with mid to upper level clouds passing
overhead. A deeper marine layer will make a push inland tonight
likely impacting all sites with medium confidence on the exact
arrival. Relied on persistence in terms of timing for locations that
have gotten a ceiling the past few nights. A mixed bag of IFR and
MVFR ceilings are forecast across the region with medium
confidence for STS to go LIFR. Ceilings are expected to clear
late Thursday morning.

Vicinity of SFO...VFR with mid to high level clouds present. Onshore
winds increase through the afternoon with the potential for
occasional gusts up to 25-27 kt. SW winds remain breezy overnight
with the marine layer expected to impact both OAK and SFO with MVFR
ceilings shortly after midnight. Clouds are expected to scatter out
later tomorrow morning, around 18-19Z.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Smoke and haze from the nearby fire will
still be prevalent today. Currently monitoring the potential for
lightning from high-based thunderstorms nearby the airports, though
confidence is too low to include in the TAF. Will update and amend
as needed throughout the day. Gusty SW winds are expected at MRY
meanwhile SNS remains more NW with a lower chance for gusts. Stratus
is expected to bring low-end MVFR ceilings to both terminals before
sunset tonight and persist into late Thursday morning.


&&

.MARINE...
(Today through Monday)
Issued at 525 AM PDT Wed Aug 12 2026

Fresh to strong northwest winds will continue into early Thursday
with for the northern outer waters. Isolated near gale gusts will
continue through Wednesday morning. Seas will be rough and  around
9 to 11 feet, with wave heights slowly subsiding through Thursday.
Long period southerly swell will gradually increase  late in the
week, peaking between 16 to 18 seconds late Friday  through early
Sunday. Expect haze and smoke to limit visibility at times along
the Big Sur coast due to the Timber fire.

&&

.FIRE WEATHER...
Issued at 118 AM PDT Wed Aug 12 2026

Near-critical fire weather conditions Wednesday afternoon through
Thursday early morning across Monterey and San Benito Counties due
to high based thunderstorms. Confidence remains low for a low
probability/high impact scenario of elevated rain
showers/thunderstorms across the Central Coast from a low pressure
system that is currently 300 miles southwest of Point Conception.
Erratic/gusty outflow winds of 35-45 mph can be expected with any
elevated rain showers/thunderstorms. Lightning will pose the risk
for new fire starts and has the potential to hinder operations on
the Timber Fire in Big Sur. The areas of most concern will be in the
higher terrain above the marine layer (1,500 feet), namely the Santa
Lucia Mountains and Gabilan Range. Poor minimum daytime relative
humidity around 30% is expected in the afternoons with little-to-no
recovery overnight.

Sarment

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506-
     508-529-530.

PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Navarrete
MARINE...KR

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