FXUS66 KMTR 091008
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
308 AM PDT Wed Sep 9 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 218 PM PDT Tue Sep 8 2026

 - Warming and drying trend will bring widespread moderate to
   major HeatRisk through Thursday

 - Cooler temperatures, closer to normal, Friday into the weekend

&&

.SHORT TERM...
Issued at 1207 AM PDT Wed Sep 9 2026
(Today through Thursday)

A northward intrusion of mainly mid and high level tropical 
moisture from the remnants of Marie continues to move in across 
the forecast area. The Tuesday evening 5 pm (00z) Vandenberg upper
air sounding showed a cloud layer as low as 16,000 feet. Cirrus 
at ~ 30,000 feet with the subtropical jet stream was evident on
the Oakland upper air sounding. Under the mid and high level
clouds, it's currently much drier to the ground with a sliver of
coastal dew point temps in the 50s to around 60F to Santa Cruz,
otherwise it is drier away from the coastline. Warm temperatures
will continue tonight with the incoming cloud layers greatly
reducing radiative cooling. Sub-cloud layer dry air does at times
tend to stay land-locked over the highly varied terrain of CA, 
until diurnal mixing, diffusion, wind transport and/or precipitation
get going to thoroughly mix in the higher humidity to ground level.

KVBX Vandenberg radar does show high based light showers recently.
GOES West lightning mapper shows spotty lightning activity to the
southwest as well and this lightning is close to the leading edge
of a mid-upper level moisture gradient. There's a history of rain
and lightning activity from earlier today well to our south, a 
signature of favorable thermodynamics and jet stream dynamics west
of strong 500 mb ridging even at 590+ heights. This bears close 
monitoring in the nearest term. 

No changes to the forecast at this time. A Heat Advisory remains
in effect for the entire forecast area until 10 PM Thursday. Strong
high pressure will result in warm morning low temperatures and 
daytime highs in the 90s to lower 100s over much of the forecast 
area. Along the immediate coastline an afternoon sea breeze may 
help nudge temperatures back down. This is a complex pattern, 
please stay tuned to the latest updates.

From the earlier forecast discussion:

Please remember these tips to help mitigate impacts from heat 
exposure:

-Suspend unnecessary outdoor activities during the extreme heat, but 
if you must be outdoors, take frequent breaks in the shade  or AC 
and drink cool water.
-Know the signs and symptoms of Heat Exhaustion vs. Heat Stroke! 
Heat Stroke can be deadly if not treated immediately by a medical 
professional. Call 911 if you suspect someone is suffering from Heat 
Stroke.
-Wear a life jacket, swim near a lifeguard, and check conditions 
before entering the water if going to a river or ocean to cool off. 
Rivers and the ocean are extremely cold, and Cold Water Shock can 
turn into paralysis and drowning if you are not careful.
-Use a cool and damp towel on your body if you do not have AC and 
are feeling hot. Or, take a cool shower or bath.
-Do not leave kids or pets in a parked car.
-Ensure pets and livestock have access to shade and water.

&&

.LONG TERM...
Issued at 1207 AM PDT Wed Sep 9 2026
(Friday through next Tuesday)

The main concern is the short term. 

A late week and weekend cooling trend remains in the forecast. 
The strong ridge over our forecast area will weaken. Dry weather 
is forecast.

&&

.AVIATION...
(12Z TAFS)
Issued at 303 AM PDT Wed Sep 9 2026

VFR conditions are expected to continue under a blanket of high 
clouds. Light offshore flow will continue to disrupt the marine 
layer today, and high clouds are suppressing radiative cooling 
this morning. These factors are both contributing to the high 
confidence VFR forecast across the terminals today. An afternoon 
sea breeze will easily overpower the offshore gradient, with a 
moderate to fresh breeze expected in the afternoon and evening. 
More consistent onshore flow is expected to return by Thursday, 
bringing low clouds back into play.

Vicinity of SFO...High confidence in VFR conditions through the TAF 
period. Winds are currently light and variable but the NW sea breeze 
will take hold this afternoon. Winds reached 18KT Tuesday and will 
be similar this evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...While it's hard to tell exactly what's 
happening under the high clouds, high resolution models are 
indicating a 10% chance for ceilings at both MRY and SNS by 18Z this 
morning. The much more likely scenario is for VFR conditions to 
persist through the TAF period under high clouds for much of the 
day. Light drainage winds in the morning will flip to a moderate 
onshore breeze in the afternoon. 

&&

.MARINE...
(Today through Monday)
Issued at 303 AM PDT Wed Sep 9 2026

A moderate NW breeze and moderate seas will continue through
Thursday. By Friday, a tighter pressure gradient will cause a
steady  increase in wind speed through the weekend, with a strong
NW breeze  expected Saturday and Sunday. A moderate SW swell from
distant  tropical cyclones will continue through the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 1 AM PDT Thursday for CAZ006-506-
     508-529-530.

     Heat Advisory until 10 PM PDT Thursday for CAZ006-502>506-
     508>510-512>518-528>530.

PZ...Small Craft Advisory from 3 PM Thursday to 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.

&&

$$

SHORT TERM...Canepa
LONG TERM....Canepa
AVIATION...Flynn
MARINE...Flynn

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Prepared by Boulder-Creek.com Weather at: Wed Sep 9 08:30:03 PDT 2026