FXUS66 KMTR 201133
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
433 AM PDT Tue Oct 20 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1200 PM PDT Mon Oct 19 2026

- Cooling trend continues through the end of the week

- Beneficial light rain showers expected mid-week

- Thunderstorms possible mid-week across southern Central Coast

&&

.SHORT TERM...
Issued at 1203 AM PDT Tue Oct 20 2026
(Today through Wednesday)

The low pressure system is already making its presence known as it 
nears our coast. Not only were there various cloud layers present on 
Monday, but some measurable rainfall has been observed in 
Northern California nearby Eureka (as of 10 PM PDT Monday). Given 
that the center of the low is still to our northwest, these 
rainbands are not expected to impact us just yet...

Overnight, the upper-level trough continues to dig southward along 
the coast and becomes fully cut-off from the main airflow by 
Tuesday. During the day, calm conditions are expected with below 
normal temperatures and infrequent wind gusts up to 20-25 mph.
Later tonight, the cut-off low begins to slowly propagate 
eastward with the first few rainbands possibly impacting the 
southern Central Coast first. Through the overnight hours, these 
rainbands begin to make their way across the rest of the Central 
Coast and Bay Area.

Rain chances increase Wednesday with the North and East Bay less 
likely to experience wetting rain (>0.10 inch) during the event. 
Chances for wetting rain increase towards the Central Coast where 
the center of the cut-off low is expected to enhance moisture 
transport onshore. The eastern portion of the system is forecast to 
have stronger wind speeds than the western portion, likely due to a 
tighter pressure gradient downstream as well as a surge in momentum 
flux from the subtropical jet stream. This roughly coincides with 
where the most moisture, instability, and lift can be found. As a 
result, thunderstorm potential (<20%) remains the greatest along the 
Central Coast. The exact timing is uncertain, though model guidance 
is suggesting the highest probabilities are during Wednesday 
afternoon. Most unstable CAPE has trended slightly downward compared 
to yesterday, though it is still highlighting the Big Sur Coastline. 
The latest SPC convective outlook has upgraded Central and Southern 
California to a marginal severe thunderstorm risk, just south of the 
Monterey County border... Even though we are not included in the 
marginal severe risk, this is too close to comfort considering the 
proximity to the Timber and Plaskett fire burn scars. As the event 
draws closer, this will be an area of special interest not only for 
the potential of debris flows if rainfall thresholds are met, but 
also gusty and erratic winds that may result from low-topped 
thunderstorms.

&&

.LONG TERM...
Issued at 1203 AM PDT Tue Oct 20 2026
(Wednesday night through Monday)

Overnight, the center of the low gradually moves across the region 
resulting in diminishing rainfall chances, though the Central Coast 
still remains with a 60-80%. Lingering rain showers persist through 
Thursday as the system continues its eastward track. Across the Bay 
Area, 20-40% rain chances persist with a 40-60% chance across the 
Central Coast.

By Friday, the trough center will be east of our area as high 
pressure gradually builds in its wake with a mean northerly wind 
flow. To balance out the recent disturbance, a slightly warmer and 
drier air mass settles over the region this weekend with seasonal 
temperatures in the 60s and 70s.

&&

.AVIATION...
(12Z TAFS)
Issued at 419 AM PDT Tue Oct 20 2026

VFR through the TAF period. High clouds remain over the area 
throughout today with ceilings gradually lowering tomorrow as
showers approach. Winds are light this morning with moderate 
onshore winds expected during the afternoon and evening. Winds
then diminish tonight overnight becoming southerly to variable. 
Rain showers arrive around 12Z tomorrow morning so have started 
mentioning shower potential for OAK and SFO while this is still
outside of the current TAF period for non 30 hour TAF sites. 
Showers will reach the Central Coast first before spreading 
northwards into the Bay Area by late morning. Expect shower 
activity to pick up at MRY and SNS shortly after 12Z tomorrow 
with the Bay Area sites following suite between 12-18Z.

Vicinity of SFO...VFR. Winds are light and southerly this morning
with moderate onshore winds (12 knots) this afternoon/evening. 
Winds decrease overnight tonight becoming variable. Shower 
chances increase Wednesday morning with light showers becoming 
more likely after 12Z. Shower activity will then pickup Wednesday
afternoon with reductions in ceilings and visibilities likely as 
heavier showers develop.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Light southerly winds continue
through late morning before moderate W to NW winds return this
afternoon and evening. Winds decrease overnight becoming southerly
to variable. Current model guidance shows showers approaching the
Central Coast around 12Z tomorrow morning. Expect temporary 
reductions in visibility and ceiling heights as stronger showers 
develop and move inland. Moderate showers become more widespread 
by the afternoon as the bulk of the rain moves in.

&&

.MARINE...
(Today through Sunday)
Issued at 419 AM PDT Tue Oct 20 2026

A light to gentle southerly breeze persists through early
Thursday with winds gradually becoming more northerly Wednesday
into Thursday. Fresh to strong northerly winds return Thursday and
continue into the weekend with near gale force gusts possible
across the northern outer waters. Moderate seas prevail with
localized rough seas across the outer waters Tuesday and Friday.
Rain showers with a chance of thunderstorms are expected late
Tuesday through Thursday, especially south of Pigeon Point.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Navarrete
LONG TERM....Navarrete
AVIATION...Kennedy
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Tue Oct 20 06:30:03 PDT 2026