FXUS66 KMTR 181228
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
428 AM PST Tue Nov 18 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1242 PM PST Mon Nov 17 2025
- Scattered showers will gradually decrease through Tuesday
morning before drier weather returns Tuesday afternoon.
- Next system brings more beneficial type rain late Wednesday
through Thursday.
&&
.SHORT TERM...
Issued at 312 AM PST Tue Nov 18 2025
(Today and tonight)
Near term weather continues to be driven by the slow moving upper
level low pressure currently parked over the Central Coast. Enough
lingering moisture and lift are present around the upper low to
generate widely scattered showers. Interesting to watch KMUX radar
imagery early Tuesday morning with shower activity pivoting
counter-clockwise around the upper low with the heaviest shower
activity over the coastal waters. Freezing level is hovering
right around 5k so cannot rule out some wet snow flakes over the
higher peaks of the Central Coast this morning. Latest CAMS keep
these scattered showers through mid-morning, but primarily out of
the Bay Area and mainly over the Central Coast. By this
afternoon, overall drying will occur with fair weather CU behind
the departing upper level. Despite some drying and sunshine, today
will be seasonably cool with highs in the 50s to near 60 (40s
higher peaks).
Subsidence behind the departing low pressure system and shortwave
ridge overhead will lead to some clearing Tuesday night into early
Wednesday. Given the recent rain and ample low level moisture some
interior valley fog will be possible tonight.
&&
.LONG TERM...
Issued at 415 AM PST Tue Nov 18 2025
(Wednesday through Monday)
Dry weather holds through most of Wednesday, but temperatures
remain on the cool side again. Cold air and daytime heating will
likely lead to fair weather CU again.
The dry weather quickly comes to an end Wednesday thanks to an
active longwave pattern over the EPac. Another robust upper level
jet becomes amplified over the EPac Wednesday leading to another
round of cyclongensis off the West Coast. A surface low is
forecast to develop in the Gulf of AK Wednesday and then deepen as
it track east. The low will ultimately drag a cold front through
NorCal Thursday. Additionally, the amplified upper level jet will
help to cut-off another upper low off the CA Thursday into Friday.
The passing front and developing upper low will bring precip back
to the region. Rain is still on track to return to the N Bay
Wednesday night and then progress S and E early Thursday. Showers
will linger through Thursday night. While this front has some
moisture, the main tap isn't overly robust despite it's origin
back to near HI. PWATs are just shy of one inch. All that being
said, guidance has been trending slightly drier with total
rainfall Wednesday through early Friday. Still looking more
beneficial than hazardous to the region. Rainfall amounts will
generally be a tenth or two and up to three quarters of an inch N
Bay and coastal mountains. If the upper low over produces, the end
higher end of precip amounts (1 in 10 chc) would double those
rainfall amounts. One low confidence portion is the exact timing
of the front and its potential impact to the Thursday morning
commute.
Warming and drier conditions are expected to develop Friday and
over the weekend. Given another burst of rain, night and morning
fog will likely be the bigger weather impacts this weekend.
&&
.AVIATION...
(12Z TAFS)
Issued at 428 AM PST Tue Nov 18 2025
Mix of MVFR and VFR conditions across the board. An upper level low
continues to slide down the coast of California and is bringing
lingering scattered showers across the Central Coast. This is
keeping our cloud cover patchier with sites going from clear skies
to BKN/OVC clouds for short periods of time before clearing out
again. CIGs are predominantly expected to be VFR but patchy MVFR
CIGs may temporarily develop through the remainder of the morning.
Any MVFR CIGs that do develop are expected to be short in duration
and not the prevailing weather condition. As the low moves
southwards, CIGs will clear across the region with clear skies
expected for the afternoon/evening hours. Guidance shows MVFR CIGs
returning towards the end of the TAF period. For now, leaned
towards later arrivals between 09-12Z when creating the 12Z TAFs but
there were some outliers, notably MOS guidance, that favored earlier
returns closer to 06Z. The upper level low continues to dictate
winds across the region with offshore winds expected to shift back
to west/northwest by late this morning as the low exits to our south.
Vicinity of SFO...VFR becoming MVFR tonight. Temporary MVFR CIGs may
develop through the remainder of the morning as the low exits
southwards but any MVFR CIGs that do develop should be short lived
and will not be the prevailing weather. Shower chances have largely
diminished at SFO with higher chances to the south over the marine
environment off of the Central Coast. Moderate confidence in stratus
returning overnight - for now placed the stratus return closer to
12Z but MOS guidance does show potential for stratus as early as
09Z. Offshore winds will gradually become westerly this afternoon
and peak around 12 knots. Winds ease overnight and shift more
southwesterly to southerly.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR expected through the TAF period.
Temporary MVFR CIGs may develop through this afternoon as the low
moves southwards but confidence is moderate that these will be
temporary and will clear quickly. Radar shows a few scattered
showers lingering offshore of the Central Coast with scattered,
light showers drifting into the Monterey Peninsula. Kept vicinity
showers in for both MRY and SNS through late this morning when
shower chances start to drop off. Offshore winds will gradually
shift west/northwesterly this afternoon and strengthen to around 10
knots.
&&
.MARINE...
(Today through Sunday)
Issued at 428 AM PST Tue Nov 18 2025
Scattered showers diminish by this afternoon. Wave heights remain
elevated and winds remain fresh to strong with near gale force
gusts possible across the northern waters through late Tuesday.
Marine conditions briefly improve Wednesday as wave heights abate
and winds diminish. A weak system will arrive late Wednesday into
Thursday bringing a return of light rain and hazardous marine
conditions. Locally fresh to moderate winds and significant wave
heights between 10 to 15 feet are expected Thursday into the
weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM this morning to 9 PM PST this
evening for Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory until 3 AM PST Wednesday for Pigeon Pt to
Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Kennedy
MARINE...Kennedy
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Prepared by Boulder-Creek.com Weather at: Tue Nov 18 08:30:03 PST 2025
From the National Weather Service
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