FXUS66 KMTR 111248
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
529 AM PDT Tue Aug 11 2026
...New FIRE WEATHER...
.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...
(12Z TAFS)
Issued at 422 AM PDT Tue Aug 11 2026
Satellite shows stratus and fog /MVFR-IFR-LIFR/ developing and
moving inland on onshore winds; winds supported by 1.8 mb SFO-SAC
pressure gradient. Otherwise it's VFR. The marine layer depth
remains approximately 1300 to 1800 feet. Stratus and fog will mix
out by late morning with VFR prevailing through the afternoon.
Stratus, fog and patchy light drizzle /MVFR-IFR-LIFR/ develop and
move inland tonight and Wednesday morning.
Vicinity of SFO...Stratus /MVFR/ developing this morning, it may
temporarily lower to IFR. VFR is forecast to return 18z today. West
to northwest wind 5 to 15 knots except 15 to 25 knots in the
afternoon and evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus and fog /IFR-LIFR/ will mix out
to VFR late morning to early afternoon with VFR continuing through
the afternoon. Stratus, fog and patchy light drizzle /IFR-LIFR/
develop and move inland tonight and Wednesday morning. West to
northwest winds 5 to 15 knots.
&&
.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...Canepa
MARINE...Canepa
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea
Prepared by Boulder-Creek.com Weather at: Tue Aug 11 10:30:03 PDT 2026
From the National Weather Service
|