FXUS66 KMTR 192327
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
427 PM PDT Wed Aug 19 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 147 PM PDT Wed Aug 19 2026

 - Compressed marine layer today, increases Thursday into the weekend

 - A gradual cooling kicks off Thursday and continues into the 
   weekend

 - Elevations above about 1000 feet will have warm temperatures
   and RH values in the teens Thursday morning and afternoon

&&

.SHORT TERM...
Issued at 147 PM PDT Wed Aug 19 2026
(This evening through Thursday night)

Little change to the forecast as we shift from quasi-ridging to more 
zonal flow in the upper levels over the next day. An upper level low 
will slowly advance towards the West Coast, nudging the Desert 
Southwest high slightly eastward. This will allow a cooling tend to 
start on Thursday, in addition to the marine layer deepening and 
onshore flow increasing. The marine layer should get to 1000-1200ft 
by Thursday morning, leading to another night with wide spread 
stratus, patchy fog, and patchy coastal drizzle. Elevations above 
the marine layer, wont' be as lucky and will continue to be warm and 
dry above it. Clouds begin to clear by early to mid morning, with 
the stratus retreating to the coast by late morning. High clouds 
look to return to the forecast tomorrow which should leave us with 
partly to mostly cloudy skies. High temperatures will likely be a 
couple of degrees cooler than Wednesday. 

&&

.LONG TERM...
Issued at 147 PM PDT Wed Aug 19 2026
(Friday through next Tuesday)

The upper level low continues to track towards the West Coast, with 
the trough elongating southwards and the shortwave or closed low 
moving towards the PacNW by Saturday. Troughing holds over the 
region through early next week, which will lead to temperatures 
being anywhere from 5 to 15 degrees below their seasonal normal. 
Stratus looks promising each night through at least Saturday 
morning, with the marine layer potentially compressing Saturday 
night into Sunday morning. Models suggest it could deepen again 
Sunday night into Monday morning, which may lead to more widespread 
stratus. 

&&

.AVIATION...
(00Z TAFS)
Issued at 426 PM PDT Wed Aug 19 2026

Currently VFR with the exception of HAF which is IFR. Another 
persistence forecast on tap with little change in the pattern. As 
such, moderate to high confidence in IFR ceilings returning to all 
terminals tonight. Further deterioration to LIFR is expected at 
coastal terminals and STS. If the marine layer undergoes 
compression, conditions will further deteriorate with less 
inland extent expected. Diurnal winds will prevail.

Vicinity of SFO...Currently MVFR due to haze with northwesterly 
flow. Moderate confidence in an IFR ceiling returning tonight with 
VFR by late-morning. Diurnal winds will prevail.

SFO Bridge Approach...Similar to SFO. 

Monterey Bay Terminals...Currently VFR with westerly flow at MRY and 
VFR with northwesterly flow at SNS with IFR stratus lurking off the 
coast. High confidence in IFR conditions retuning early this evening 
with further deterioration to LIFR expected. VFR is expected by 
tomorrow afternoon. Diurnal winds will prevail.

&&

.MARINE...
(Tonight through next Monday)
Issued at 426 PM PDT Wed Aug 19 2026

Moderate to fresh northwesterly breezes with strong gusts across
the northern outer waters and along the coastal jet regions will
bring hazardous conditions for small craft periodically through
the weekend. Breezy fresh winds are expected across the San Pablo
Bay and the San Francisco Bay with locally stronger gusts possible
where terrain promotes wind funneling. Rough seas in the outer
waters will subside Thursday with moderate seas prevailing by
Friday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for Pt Arena to Pt 
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt 
     Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Thursday for Pigeon 
     Pt to Pt Pinos 0-10 nm.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Sarment
MARINE...RGass

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Prepared by Boulder-Creek.com Weather at: Wed Aug 19 20:30:03 PDT 2026