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