FXUS66 KMTR 121226
AFDMTR

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

...New AVIATION, MARINE...

.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...
(12Z TAFS)
Issued at 525 AM PDT Wed Aug 12 2026

The marine layer is at roughly 1500-2000ft this morning, but the 
view from satellite is currently blocked due to high clouds moving 
in. Expect the stratus to hold where it is at, with minimal 
expansion into the South and East Bay valleys. Elsewhere, MVFR to IFR 
cigs are being observed where there is stratus with the exception 
being KSTS where cigs are LIFR. Look for conditions to improve by 
mid to late morning, with high clouds lingering. Tonight, the 
stratus is expected to return. There's a curve ball as an upper low 
and an additional disturbance move through. Will this keep the 
stratus at hand, allow it to expand or will the pattern shift up a 
bit with the high cloud? Opted to keep the pessimistic forecast of 
stratus returning tonight and into tomorrow morning, but this will 
need to be monitored. Moderate to high confidence in the forecast 
through Wednesday evening. Moderate confidence for Wednesday evening 
into Thursday morning. 

Vicinity of SFO...Stratus detections is a bit difficult this morning 
due to the high clouds overhead. Looking at webcams and stations 
around the San Francisco Bay, there are some MVFR cigs present. 
Current thinking is we should stay VFR with only a FEW or SCT MVFR 
cigs possible through mid to late morning. High clouds linger into 
the afternoon with the next challenge being winds. Some guidance 
keeps SSW to SW through the day, while others try to bring onshore 
winds back. May need to adjust the winds by the 15Z update if the 
trend continues for SW this afternoon. Tonight, guidance tries to 
bring back stratus, but confidence is too low to sock us in with low 
clouds. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Another cloudy start to the morning, as 
stratus seeped into the terminals early Tuesday evening. Look for 
conditions to clear by mid to late morning, retreating to the coast. 
Models show an afternoon of VFR conditions, but it will dependent on 
on just how far back the stratus pulls. Tonight, expect it to return 
early on with Thursday morning potentially being interesting. An 
upper level disturbance swings just to our north, which could bring 
some drizzle to the terminals. This hasn't been added to the 
forecast due to timing issues if this were to happen. 


&&

.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...KR
MARINE...KR

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Prepared by Boulder-Creek.com Weather at: Wed Aug 12 08:30:02 PDT 2026