FXUS66 KMTR 181222
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
522 AM PDT Sun Oct 18 2026
...New AVIATION, MARINE...
.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...
(12Z TAFS)
Issued at 522 AM PDT Sun Oct 18 2026
Satellite imagery this morning shows stratus from roughly Bodega Bay
down to the Santa Cruz Coast and portions of the Monterey Bay. The
marine layer looks to be around 500ft so far, which could lead to
some patchy fog development around sunrise. Stratus and any fog that
develops should quickly erode today, the exception being along the
San Mateo coast near KHAF. The question will be, will they remain
socked in with MVFR cigs, or scatter out? Elsewhere, VFR conditions
are expected into the afternoon. Stratus attempts to make a return
during the early evening hours, with low cloud penetrating a bit more
inland overnight. THe marine layer is expected to get to around
1000ft, which should bring MVFR cigs.
Vicinity of SFO...Stratus should stay west and flirt around SFO this
morning, leaving us with VFR conditions. Should clouds fill in the
next couple of hours, they'll be short lived as they'll quickly
retreat to the coast by late morning. Tonight, there's a better
chance for stratus to reach the terminal. A few models show we could
see some clouds starting to creep in by 3Z; however, most show it
happening closer between 7-10Z. MVFR cigs are expected, with the
potential IFR cigs around sunrise. Clouds should clear by mid to
late Monday morning.
In addition to the clouds, gusty onshore winds are forecast this
afternoon and into the evening with gusts peaking around 25kt.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus is meandering around the Monterey
Peninsula, and starting to blossom just outside of KSNS. Current
thinking is we should see stratus and perhaps some patchy fog
develop around sunrise, lasting for a few hours before clearing
out. Onshore flow picks up for the afternoon, with winds weakening
after sunset. Stratus should develop a bit earlier this evening,
leading to night of MVFR to then IFR cigs.
&&
.MARINE...
(Today through Friday)
Issued at 522 AM PDT Sun Oct 18 2026
Winds will increase today with moderate to fresh northerly
breezes prevailing through Monday with locally strong breezes
across the northern outer waters. Widespread hazardous conditions
will spread across the coastal waters as a result Sunday
afternoon, likely continuing into Monday. Moderate seas will
prevail across the inner waters with rough seas across the outer
waters through Tuesday. Light rain showers are expected Monday
night through Wednesday.
&&
.BEACHES...
Issued at 1002 AM PDT Sat Oct 17 2026
Hazardous beach conditions will be present at Pacific Coast beaches
through Sunday and likely into next week. 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 through 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...KR
MARINE...KR
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Prepared by Boulder-Creek.com Weather at: Sun Oct 18 06:30:03 PDT 2026
From the National Weather Service
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