FXUS66 KMTR 130418
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
918 PM PDT Wed Aug 12 2026

...New AVIATION, MARINE...

.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...
(06Z TAFS)
Issued at 919 PM PDT Wed Aug 12 2026

Currently VFR for majority of terminals with KHAF and Monterey Bay
sites in MVFR/IFR. Deeper marine layer (1800ft to 2000ft) and 
stronger onshore flow will result in more widespread stratus 
intrusion while an offshore eddy will continue to complicate 
timing of MVFR/IFR ceilings for the Bay Area, especially KSFO. A 
quasi- stationary upper level low and associated trough at our 
latitude will produce gusty onshore flow at times through the TAF 
period.

Vicinity of SFO...Gusty onshore flow will persist through much of
the TAF period with a better inland push overnight than we've seen
the past week. However, as a mentioned above, an offshore eddy
will continue to complicate timing and coverage of MVFR/IFR
ceilings, especially at KSFO.

SFO Bridge Approach...Expect MVFR/IFR ceilings in vicinity of KSFO
even if not measured at the terminal.

Monterey Bay Terminals...Quasi-stationary upper level low will
eventually produce and maintain IFR/LIFR ceilings overnight
through at least late morning, and possibly into the afternoon
especially at KMRY. A slight chance, but low confidence of KMRY
remaining socked in through the forecast period.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 919 PM PDT Wed Aug 12 2026

Fresh to strong northwest winds with isolated gale force gusts
will ease by early Thursday morning, with rough seas becoming
moderate by Thursday evening. Long period southerly swell will
gradually increase Thursday reaching 16 to 18 seconds (possibly
higher at times) by Friday and continuing through the remainder of
the weekend. Visibility may decrease due to haze and smoke nearby
the Big Sur coastline 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...JM
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Wed Aug 12 22:30:02 PDT 2026