447
FXUS66 KMTR 181152
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
452 AM PDT Tue Aug 18 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 428 PM PDT Mon Aug 17 2026

 - Slight warming trend continues through Wednesday

 - Marine layer remains compressed through mid week

 - Light winds continue to be mitigating factor for
   Timber Fire

&&

.SHORT TERM...
Issued at 1145 PM PDT Mon Aug 17 2026
(Today and tonight)

Mid/upper level clouds continue to stream from southwest to
northeast across our area with mild temperatures expected once again
overnight into early Tuesday morning. The mild start to the day will
help bump temperatures at least a few degrees (away from the marine
layer) higher from Mondays values as the influence from upper level
ridging over the Four Corners nudges west. H85 temperatures will be
around 23-24C by peak heating which is in the 90th percentile for
this time of year. With that, the warmest temperatures will be at
higher elevations, especially the East Bay Hills and Santa Lucias,
including higher portions of the Timber Fire. Fortunately, light
winds continue to be a mitigating factor to more rapid spreading of
the fire.

&&

.LONG TERM...
Issued at 1145 PM PDT Mon Aug 17 2026
(Wednesday through Monday)

Warmer temperatures persist Wednesday under the influence of the
aforementioned ridging aloft, however the troughing over the EPAC
pushes back east and slightly north by Thursday with a sharpening
trough axis well offshore. The cool down for Thursday through the
remainder of the extended forecast will be subtle and gradual.
There are at least two tropical waves that will pass well to our
south, the first on Thursday followed by a more organized wave
with tropical development possible by the end of the weekend into
the beginning of next week. We`ll be keeping an eye on any
midlevel moisture advection north from either of the two waves.

&&

.AVIATION...
(12Z TAFS)
Issued at 442 AM PDT Tue Aug 18 2026

IFR-LIFR everywhere as stratus pushes into the Bay Area and
Central Coast. Models are not capturing the current marine layer
well and continue to show it compressing to ~1000 feet while it
stays around 1500 to 2000 feet in actuality. Opted to follow a
general persistence forecast for clearing by late morning and for
stratus return later tonight. Stratus will be more persistent
along the coast, potentially impacting HAF all day, with only a
brief period of VFR at MRY and SNS. Some potential for fog along
the coast this morning with moderate reductions in visibility at
HAF, MRY, and SNS already being observed. Given the relatively
stable forecast, moderate confidence in a persistence forecast
again tonight with a mix of IFR to LIFR conditions returning this
evening and coastal reductions in visibility early tomorrow
morning.

Vicinity of SFO...IFR ceilings generally persist until late this
morning. LAMP guidance suggests some potential for ceilings to go
from IFR to MVFR shortly before clearing around 18Z. Gusty onshore
winds are expected this afternoon and evening before winds ease
overnight. Opted for a more persistence based forecast of IFR
ceilings again tonight with stratus returning around 05Z and
lasting through the rest of the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...LIFR-IFR ceilings continue through late
morning with moderate confidence in clearing around 18/19Z. VFR
conditions briefly return this afternoon before IFR to LIFR
conditions redevelop early this evening into the overnight hours.
Followed persistence to show the lowering of stratus from IFR to
LIFR with substantial reductions in visibility becoming more
likely closer to 12Z. Moderate onshore winds expected this
afternoon before winds ease overnight.

&&

.MARINE...
(Today through Sunday)
Issued at 442 AM PDT Tue Aug 18 2026

A fresh to strong northwest breeze will develop across the outer
waters today and extend into the inner waters tonight into
tomorrow. Winds then remain elevated through the end of the
forecast period. Locally stronger winds are possible in the
coastal jet regions north of Point Reyes and along the Big Sur
coast. Seas build to 7 to 9 feet Tuesday and Wednesday before
subsiding late week.

&&

.FIRE WEATHER...
Issued at 200 PM PDT Mon Aug 17 2026

The marine layer will gradually compress over the next 24 to 36
hours, as high pressure builds over the region. As a result, nocturnal
drying will be possible through at least mid-week for the higher
elevations, with more widespread fair to moderate recoveries
developing over the higher elevations, especially in and around
the Timber Fire.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Kennedy

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