FXUS66 KMTR 182322
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
422 PM PDT Fri Sep 18 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1057 PM PDT Thu Sep 17 2026
- Warming trend through Saturday
- Brief cooldown Sunday
- Notable warming trend next week
&&
.SHORT TERM...
Issued at 1120 AM PDT Fri Sep 18 2026
(This afternoon through Saturday)
The marine layer compressed to around 1,700 feet this morning. That
trend will continue over the next 24 hours as a short wave ridge
builds over the area. While the W-E gradients are all still weakly
positive (SFO-WMC +1.9mb, SFO-SAC +1.2mb) we did see some NE,
offshore winds this morning. The gradients will continue to drop and
become negative this afternoon, however the onshore sea breeze will
overpower any offshore flow during the day.
In response to the building ridge and compressed marine layer,
Inland temperatures will be roughly 5 degrees warmer today compared
to yesterday, and another 5 degrees warmer Saturday. While less
expansive, the marine layer will continue to keep high temps along
the coast in the 60s with low clouds and possible fog in the
morning. The offshore wind gradient will peak overnight, though
the strength still isn't overly impressive. Still, NE winds with
gusts up to 20-30 mph are possible across the interior North Bay
Mountains late tonight and early Saturday morning.
&&
.LONG TERM...
Issued at 1120 AM PDT Fri Sep 18 2026
(Saturday night through next Thursday)
The pattern remains quite active in the long term forecast, although
the next few features are pretty weak. Saturday's ridge is
quickly replaced by a weak cut-off low approaching from the west
through the day Sunday. This will reverse the warming trend and
allow the marine layer to expand a bit. This low will gradually
slide overhead by Monday morning, giving us a good chance for
drizzle.
By Tuesday another ridge will start to build from the west, kicking
off a warming trend that will last through the rest of the week.
The ECMWF ensemble shows a 90% chance that the 850 mb temperature
gets above 20C on Wednesday with a mean around 23C. 23C is above
the the 90th percentile for this time of year and would bring
inland surface temperatures back into the 90s.
&&
.AVIATION...
(00Z TAFS)
Issued at 421 PM PDT Fri Sep 18 2026
Some MVFR ceilings linger at the immediate coast but most of the
region enjoys VFR ceilings and a gentle to moderate onshore wind
through the evening hours. A compressing marine layer should keep
stratus within the inland valleys through the night with generally
low-end MVFR-LIFR ceilings expected. Stratus will retreat to the
immediate coast through Saturday morning with onshore winds resuming
in the afternoon, expected to be weaker than today's winds.
Vicinity of SFO... VFR through the late evening and early overnight
hours with strong northwest winds gradually diminishing in the
evening hours. MVFR-IFR stratus comes into the terminal area around
06-08Z with the stratus deck expected to set up just to the north of
the terminal before expanding southwards. Stratus mixes out Saturday
morning with breezy northwest winds resuming in the afternoon, with
clouds returning in the evening hours.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... VFR conditions expected to continue for
the next couple hours near MRY and into the evening at SNS, with a
moderate northwest to west breeze expected into the evening hours.
IFR ceilings will develop this evening and overnight as the winds
become light, with some potential for LIFR ceilings at MRY. Stratus
retreats to the immediate coast Saturday morning with breezy winds
resuming in the afternoon.
&&
.MARINE...
(Tonight through next Wednesday)
Issued at 421 PM PDT Fri Sep 18 2026
Moderate to fresh winds continue this afternoon into the weekend.
Strong gusts up to 30 kt are possible across the northern coastal
waters, Big Sur coastal jet region, and the Monterey Bay region
through Saturday. Winds gradually diminish across the southern
coastal waters by Saturday evening, but remain elevated across the
north. Slight to moderate wind driven seas persist through the
weekend and steadily build to rough by early next week.
&&
.FIRE WEATHER...
Issued at 429 AM PDT Fri Sep 18 2026
The marine layer is expected to begin redeveloping itself through
the day as a ridge develops over the state. By the evening hours the
marine layer should be around 1000-1500 feet, along with attendant
impacts of stratus development below the marine layer inversion and
poor overnight humidity recoveries within and above the thermal
belts. As the ridge develops, weak offshore flow is possible
Saturday morning, particularly across the higher elevations of the
North and East Bay.
DialH
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Saturday for Mry Bay-Pigeon
Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10
nm.
Small Craft Advisory until 3 AM PDT Sunday for Pt Arena to Pt
Reyes 0-10 nm.
Small Craft Advisory from 3 PM Saturday to 3 AM PDT Sunday for
Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
Blancas 0-10 nm.
Small Craft Advisory from 9 PM this evening to 3 AM PDT Sunday
for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-
60 NM.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...Flynn
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Prepared by Boulder-Creek.com Weather at: Fri Sep 18 18:30:03 PDT 2026
From the National Weather Service
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