FXUS66 KMTR 122119
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
219 PM PDT Wed Aug 12 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 218 PM 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 this weekend into next week
- Minor coastal flooding for bayshore locations along the San Francisco
Bay, San Pablo Bay, and Monterey Bay through Thursday morning
&&
.SHORT TERM...
Issued at 218 PM PDT Wed Aug 12 2026
(This evening through Thursday night)
Isolated thunderstorm potential continues through this evening along
the Central Coast with increasing confidence compared to this
morning. Radar shows a line of storms developing off of the Big Sur
coastline and moving in to Monterey County. As of this morning/early
afternoon, we have cells moving inland in the vicinity of the Timber
Fire which produced lightning both offshore and on land. This cell
backbuilt to the southwest with additional cells developing in the
wake of the original (inland) cell over the marine environment.
These additional storms have been slowly moving inland in the
vicnity of the Timber Fire and may also become favorable to produce
lightning. Any of these cells will be capable of producing gusty,
erratic wind and dry lightning with any rain evaporating before
reaching the surface due to the elevated storm nature. Fuels are
incredibly dry right now with near critical fire weather concerns
across Monterey and San Benito Counties. If dry lightning occurs, it
is likely to result in additional fire starts. Residents of interior
Monterey and San Benito County (particularly along and within the
higher terrain) should stay weather aware, avoid unnecessary
activities that may result in sparks/fire, and follow guidance from
local officials. Confidence is highest in thunderstorms over the
elevated terrain with orographic lift acting as the trigger for
storms to develop. This is an ongoing event and we will be paying
close attention to the radar this afternoon and evening as it
evolves.
Tonight into tomorrow, a low pressure system offshore will move into
the Central Coast and bring additional chances for thunderstorms
through Thursday morning. HRRR guidance shows several hundred
joules/kg of MUCAPE moving across the Central Coast tonight into
early Thursday with decent upper level support (700-500 mb lapse
rates between 7-8 C/km) and lingering monsoonal moisture. Given that
storms are currently occurring along Big Sur, it is likely that we
will see additional storms again tonight through tomorrow morning
across the Central Coast. Storms tonight and tomorrow morning could
potentially reach as far north as the Santa Cruz Mountains and the
South Bay. Storms are most likely to form along the higher terrain
and be driven by orographic lift.
&&
.LONG TERM...
Issued at 218 PM PDT Wed Aug 12 2026
(Friday through next Tuesday)
Thunderstorm chances diminish after Thursday with drier conditions
to prevail into next week. Temperatures will remain well below
normal across the Bay Area and Central Coast as upper level
troughing persists through this weekend. This will keep highs in the
60s closer to the shoreline and in the 70s to mid 80s across the
interior. The exception will be the interior Central Coast where
highs will warm into the upper 80s to low 90s late weekend into
early next week. Temperatures gradually warm next week as ridging
pushes into the Desert Southwest from the Central US and troughing
continues over the Eastern Pacific Ocean.
&&
.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 3 PM PDT Thursday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Navarrete
MARINE...KR
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Prepared by Boulder-Creek.com Weather at: Wed Aug 12 14:30:03 PDT 2026
From the National Weather Service
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