Technical NOAA Weather Discussion

FXUS66 KMTR 190514
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1014 PM PDT Fri Sep 18 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1057 PM PDT Thu Sep 17 2026

 - Warming trend through Saturday

 - Brief cooldown Sunday

 - Notable warming trend next week

&&

.UPDATE...
Issued at 908 PM PDT Fri Sep 18 2026

Satellite imagery shows stratus clouds returning to the coastal
regions from Bodega Bay down to Davenport and again from the
Elkhorn Slough to Point Sur. There is also stratus flow into the 
East Bay west of the Berkeley-San Leandro Hills and through the 
Petaluma Gap. Latest observations suggest that the marine layer is
beginning to redevelop at around 1000-1500 feet, allowing stratus
to come rather far inland tonight.

DialH

&&

.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...
(06Z TAFS)
Issued at 1014 PM PDT Fri Sep 18 2026

Stratus is making its way inland bringing a mix of MVFR to IFR 
ceilings to most terminals tonight. Onshore winds ease overnight 
with their wind direction largely influenced by local terrain. By 
Saturday morning, winds shift onshore again and increase to moderate 
through the day. Most terminals will develop borderline MVFR-IFR 
ceilings and may intermittently jump between the two categories. 
Relied on persistence for STS with model guidance showing a high 
chance for another round of fog early Saturday morning. Low to 
medium confidence on whether APC, HAF, OAK, and MRY will drop to 
LIFR overnight. Current TAF hints at the possibility of borderline 
IFR-LIFR ceilings at the previously mentioned sites. Overall, medium 
confidence on the exact ceiling heights and clearing times. HAF 
might be the only terminal who does not clear on Saturday. If it 
does, it will be for a short period.

Vicinity of SFO...Ceiling heights may jump between MVFR-IFR through 
the course of the night with light onshore breezes. Medium 
confidence on exact clearing time on Saturday as ceilings may 
persist as late as 20Z (1 PM). Moderate westerly winds increase 
through the afternoon and ease by sunset. Saturday evening shows a 
promising return for stratus as early as sundown, though low to 
medium confidence on the exact return time.

SFO Bridge Approach...Delayed arrival of stratus tonight compared to 
SFO. Though, ceilings and wind pattern will generally be similar to 
SFO.

Monterey Bay Terminals...IFR ceilings have already filled over MRY 
and are slowly making their way over to SNS via current satellite 
imagery. LIFR ceilings may develop intermittently overnight with 
slight impacts to visibility. Onshore winds become light and 
variable overnight. As stratus clears tomorrow morning, a moderate 
onshore flow will develop through the afternoon. A similar stratus 
pattern is expected again Saturday evening. 

&&

.MARINE...
(Tonight through next Thursday)
Issued at 908 PM PDT Fri Sep 18 2026

Moderate to fresh northwest winds persist through 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 briefly diminish across the southern
coastal waters Saturday morning, but increase again to fresh by
Saturday afternoon. Slight to moderate wind driven seas prevail
this weekend and steadily build to rough 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 Pigeon Pt to Pt 
     Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt 
     Reyes 10-60 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.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Navarrete
MARINE...Navarrete

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Prepared by Boulder-Creek.com Weather at: Fri Sep 18 22:30:03 PDT 2026
From the National Weather Service