123
FXUS66 KMTR 111833
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1133 AM PDT Tue Aug 11 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1245 AM PDT Tue Aug 11 2026

 - Up to a 15% chance for elevated rain showers/thunderstorms
   Wednesday across the Central Coast

 - Cooling trend through Thursday, gradual warming trend Friday
   through the weekend will bring well below normal temperatures

 - Minor coastal flooding for bayshore locations along the San Francisco
   Bay, San Pablo Bay, and Monterey Bay through Thursday morning

&&

.SHORT TERM...
Issued at 1245 AM PDT Tue Aug 11 2026
(Today and tonight)

Cooling trend continues today as upper-level shortwave troughing
deepens off the West Coast. The associated lift will deepen the
marine layer and bring a chance for drizzle to coastal areas. The
Timber Fire in Big Sur will continue to bring smoke and haze to the
Central Coast via light southwesterly transport winds from the
aforementioned troughing. Ample moisture and sufficient instability
will bring up to a 10% chance for elevated rain showers tomorrow.
The relatively greatest chances are across the Interior Mountains of
Monterey and San Benito Counties. The primary hazard would be
erratic/gusty outflow winds with dry low levels and DCAPE near 1000
J/kg. Minor coastal flooding is expected during the highest high
tide (evening/overnight) for bayshore locations along the San
Francisco Bay, San Pablo Bay, and Monterey Bay through Thursday
morning.

&&

.LONG TERM...
Issued at 1245 AM PDT Tue Aug 11 2026
(Wednesday through Monday)

A reinforcing trough Wednesday will bring widespread below normal
temperatures, deepen the marine layer further, and bring chances for
coastal drizzle through Thursday. It may also act as the trigger for
elevated rain showers/thunderstorms as it overlaps with an influx of
monsoonal/sub-tropical moisture and sufficient instability. The best
chances are across the Central Coast on Wednesday, more specifically
the southern and eastern portions. While confidence is low, this
would be a high-impact scenario with erratic/gusty outflow winds and
the potential for new fire starts. A gradual warming trend is
expected Friday through the weekend as upper-level ridging builds in
from the southeast; however, temperatures will still remain well
below normal.

&&

.AVIATION...
(18Z TAFS)
Issued at 1133 AM PDT Tue Aug 11 2026

Stratus has retreated to the coastline where it`ll remain for the
rest of the day. Widespread VFR throughout the day with moderate
onshore breezes increasing in the afternoon before easing around
sunset. The marine layer pushes onshore again, impacting coastal
sites first before sunset. The stratus will then continue its push
to inland sites overnight, around/after midnight. Medium confidence
on how expansive the stratus layer will be tonight considering the
transition period we are in with the passing upper level trough. The
trough has the potential to deepen the marine layer up to 1800-2000
feet. As a result, low confidence on whether SJC will develop an
MVFR ceiling early Wednesday morning as it is dependent on marine
layer depth. Overall, expect a mixture of low-end MVFR to IFR
ceilings with a similar clearing time as today (17-18Z Wednesday).

Vicinity of SFO...VFR into the evening with moderate northwest winds
increasing this afternoon to 15-18 kt. Higher confidence for OAK to
develop an MVFR ceiling around midnight this TAF period. Low to
medium confidence for SFO to develop a ceiling given the recent
trend, but hinted at the potential for MVFR ceilings to develop
shortly after OAK. Any cloud ceiling that develops south of the Bay
Bridge is expected to clear late Wednesday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the afternoon with smoke/haze
in the local airspace due to a nearby fire on the Big Sur coastline.
Onshore winds increase through the afternoon and decrease through
the evening/overnight. Low-end MVFR to IFR ceilings are expected to
impact both terminals early this evening before sunset. Coastal
drizzle is possible in the overnight hours, but currently have low
confidence on exactly when and how long it will last.

&&

.MARINE...
(Today through Sunday)
Issued at 404 AM PDT Tue Aug 11 2026

Fresh to strong northwest winds will continue to produce rough
seas across the northern outer waters through Thursday. Long
period southerly swell will gradually increase from 15 seconds
through the middle of the week, up to 17 to 19 seconds by Friday
into Saturday.

&&

.FIRE WEATHER...
Issued at 529 AM PDT Tue Aug 11 2026

There is up to a 15% chance for elevated rain showers/thunderstorms
Wednesday across the Central Coast. Lightning was occurring with
a very slow moving 500 mb low pressure system located 400 miles
southwest of Monterey this morning. This low is forecast to move
very slowly northeastward today and tonight then start to move a
little quicker to the northeast Wednesday guided by strengthening
subtropical jet stream winds (polar jet stream winds will be located
to its northwest). This will be part of the evolving eastern Pacific
trough pattern this week mentioned in our discussion. We`ll monitor
this low closely for mainly mid level convective potential because
it`ll be located along and moving with a relatively sharp moisture
gradient. This can favor convection by locally steepening lapse
rates if there is upward forcing of a moist layer below a dry layer.
The good news is the very development of this trough this week will
be resulting in deep layered thermal troughing, increasing the
marine layer depth, the inland extent of marine influence including
stratus, fog and drizzle which will reduce surface convective
potential inland, that is, reducing the need for the atmosphere to
do work and overturn a more deeply unstable atmosphere (to restore
stability). This bears watching closely if only because summer
season features moving north from lower latitudes are complex,
potentially dynamic changing features even when 500 mb heights are
greater than 580 decameters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506-
     508-529-530.

PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Navarrete
MARINE...Canepa

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