FXUS66 KMTR 181721
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1021 AM PDT Sun Oct 18 2026
...New AVIATION, MARINE, BEACHES...
.KEY MESSAGES...
Updated at 143 AM PDT Sun Oct 18 2026
- Hazardous beach conditions continue through tonight
- Cooling trend begins today and persists into the work week
- Light rain showers possible mid-week
&&
.SHORT TERM...
Issued at 143 AM PDT Sun Oct 18 2026
(Today and tonight)
Sunday and Monday mark the transition towards cooler conditions and
breezy onshore winds. Weakening high pressure allows the marine
layer to gradually reform and deepen, though it will be short-lived.
Nonetheless, any marine layer presence aids to initiate the
beginning of a cooling trend, even if it remains shallow and
confined to the coast Sunday morning. As the upper-level trough digs
southward along the West coast on Sunday, a strengthening onshore
pressure gradient will support moderate westerly breezes. This set
up can support wind gusts around 20-25 mph through the Petaluma
Gap/Valley with the Altamont and Patterson Passes experiencing gusts
closer to 25-30 mph.
Sunday maximum temperatures are forecast to reach the 60s to low 70s
along the coast, mid 70s to mid 80s across the interior, with the
usual hot spots reaching into the low 90s. On Monday, the maximum
temperatures drop further due to increased cold air advection from
the upper-level trough. Max temperatures are forecast to reach the
mid 50s to mid 60s at the coast, mid 60s to low 70s across the
interior, with the southernmost extent of the Central Coast
remaining in the mid 70s to low 80s.
&&
.LONG TERM...
Issued at 143 AM PDT Sun Oct 18 2026
(Monday through Saturday)
Monday night has a better chance for a marine layer around 1500 ft
as the center of the upper-level trough deepens along our coastline.
By Tuesday morning however, the first round of light rain arrives
with precipitation chances around 20-40% across the Bay Area and
Central Coast. Rainfall can overpower the marine layer by saturating
the atmosphere above it, thereby mixing out. Our stratus marine
layer is typically capped by an inversion, defined as layer of the
atmosphere where temperature increases with height. Introducing rain
into the mix perturbs and cools the inversion layer causing it to
disappear resulting in no marine layer. Though there will still be
deep convective cumulus clouds present!
By Tuesday afternoon, the cut-off low pressure system slows down and
stalls directly to our west with its center approximately 300-350
miles west of San Francisco. As it stalls, a plume of moisture
originating in the Eastern Pacific gets funneled into the eastern
portion of the system from the south. By Wednesday morning, the
system begins to propagate eastward towards the Central Coast. Given
the nature of cut-off lows combined with an increased moisture flux
and terrain interactions, there is potential for precipitation to
wrap around the system's center giving way for widespread light rain
on Wednesday across the Bay Area and Central Coast (40-75% chance).
European and GFS ensemble members continue to agree on precipitable
water values above the 75th percentile on Wednesday. Rainfall
chances gradually diminish by Thursday, but cooler conditions remain
through the end of the week.
The potential for thunderstorm development (<15% chance) remains
near the Central Coast. Compared to yesterday's model runs, the
deterministic European model trended upwards in relation to most
unstable CAPE which is estimated to be around 200-350 J/kg. There is
sufficient instability and moisture available to support
thunderstorm development. Though lift is a limiting factor as it is
dependent on the alignment and trajectory of the system when it
approaches the coast.
&&
.AVIATION...
(18Z TAFS)
Issued at 1020 AM PDT Sun Oct 18 2026
Currently IFR-VFR. The marine layer was observed around 500 feet
this morning and is expected to deepen through the TAF period.
Stratus is off the coast with a feed through the Golden Gate Gap.
With the deepening of the marine layer, moderate confidence in MVFR
conditions returning to all terminals tonight as it's able to
penetrate farther inland. Onshore winds will prevail.
Vicinity of SFO...Currently VFR with northwesterly flow. Moderate
confidence in an MVFR ceiling developing at the terminal tonight,
likely early. The San Bruno Gap has been able to hold off stratus so
far, but if the marine layer deepens to around 1,000 feet, there
will be nothing stopping IFR/MVFR stratus from reaching the terminal
earlier. Westerly/Northwesterly winds will prevail, becoming gusty
in the afternoon and evening.
SFO Bridge Approach...The San Mateo Bridge Approach will likely have
clouds at or below FL070 from 04Z to 17Z.
Monterey Bay Terminals...Currently VFR and calm at both terminals.
Moderate confidence on MVFR conditions returning to the terminals
tonight. Diurnal winds will prevail.
&&
.MARINE...
(Today through Friday)
Issued at 1020 AM PDT Sun Oct 18 2026
Moderate to fresh northwesterly breezes will prevail through
Monday, bringing widespread hazardous conditions across the
coastal waters Sunday afternoon. Winds will diminish and back to
become southerly Tuesday and Wednesday before returning to
moderate to fresh northerly breezes Thursday. Rough seas across
the outer waters will subside to become moderate Monday,
rebuilding to become rough Tuesday. Light rain showers are
expected Tuesday through Thursday.
&&
.BEACHES...
Issued at 1020 AM PDT Sun Oct 18 2026
Hazardous beach conditions will be present at Pacific Coast beaches
Sunday. Long period southerly/southwesterly swell will bring an
increased risk for sneaker waves and strong rip currents with
breaking waves of 7 to 12 feet. Remain off jetties, piers, rocks,
and other waterside infrastructure as waves can sweep across the
shoreline without warning, pulling people into the sea. Remain out
of the water to avoid hazardous surf with strong rip currents and
never turn your back on the ocean!
Sarment
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement until 9 PM PDT this evening for CAZ006-
505-509-529-530.
PZ...Small Craft Advisory until 9 PM PDT this evening for Pt Arena to
Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
evening for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt
Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt
Reyes to Pigeon Pt 0-10 nm.
&&
$$
SHORT TERM...Navarrete
LONG TERM....Navarrete
AVIATION...Sarment
MARINE...Sarment
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Prepared by Boulder-Creek.com Weather at: Sun Oct 18 12:30:04 PDT 2026
From the National Weather Service
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