FXUS66 KMTR 091917
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1217 PM PDT Sun Aug 9 2026

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 1212 PM PDT Sun Aug 9 2026

 - Widespread moderate with areas of major HeatRisk for the 
   interior Sunday

 - Elevated to near-critical fire weather conditions in the 
   higher terrain through Monday

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

&&

.SHORT TERM...
Issued at 1212 PM PDT Sun Aug 9 2026
(This evening through Monday night)

A more compressed marine layer allowed for rapid clearing of 
stratus to the immediate coastline late this morning. As such, 
have left the Heat Advisory in place for much of the interior Bay 
Area and Central Coast through 10 PM this evening. However, 
locations under the around 500-800 foot marine layer may struggle 
to reach their afternoon maximum forecast temperatures. This is 
especially so around the San Jose region, yet the southern Santa 
Clara Valley has the potential. 

Minor coastal flooding is also expected around the time of the 
highest high tide (evening/overnight) for bayshore locations along
the San Francisco Bay, San Pablo Bay, and Monterey Bay through 
Thursday morning. The decision not to include the Pacific Coast 
was made yesterday evening when the forecast fell below the 
predicted values, yet still high enough to maintain the 
aforementioned bays. Please see the CFW product we have out for 
additional details. Also, for more on the fire weather concerns 
through early in the week, please see the Fire Weather Section of 
the AFD below. 

During this weekend's heat event, remember: 

* Stay hydrated and drink plenty of fluids.
* Wear lightweight and light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.

Afternoon temperatures are forecast to cool some 5-10 degrees on 
Monday as a weak shortwave trough develops off of the West Coast. 
As such, HeatRisk levels lower to minor with pockets of moderate.

&&

.LONG TERM...
Issued at 1212 PM PDT Sun Aug 9 2026
(Tuesday through next Saturday)

The troughing would also support coastal drizzle and/or mist each
night and morning through late week. Temperatures cool to below 
normal (as much as 20 deg F below by Friday) as a reinforcing 
upper level through develops off of the Bay Area and Central 
Coast. As this low pressure approaches the coastline late in the 
week and monsoonal moisture advects northward around the high over
the Four Corners, there is the potential for high-based 
convection. There remains a great deal of uncertainty of whether 
or not there will be enough instability aloft to support 
thunderstorms. While this is still far out in time and low 
confidence, any dry lightning would be problematic from a fire 
weather standpoint. Be sure to check back for additional details 
as we move closer to midweek.

&&

.AVIATION...
(18Z TAFS)
Issued at 1040 AM PDT Sun Aug 9 2026

Stratus is largely receding with the exception of HAF where an
eddy will keep stratus variable through the afternoon. VFR, 
outside of HAF, through this evening with breezy onshore winds 
during the afternoon/evening. Stratus returns overnight but 
confidence is mixed on the exact timing. HRRR guidance suggests a 
patchy return late tonight while HREF guidance shows a more 
traditional widespread early return of stratus. It will likely be 
a mix of both where stratus is widespread again tonight but may 
return later in the night. Initial clearing times look to be 
between 17-18Z but it could clear as early as 16Z (persistence 
forecast). 

Vicinity of SFO...Stratus is clearing over the SF Bay with VFR
conditions expected through this evening. Stratus is forecast to
return around 09-10Z and persist through late Monday morning.
Highest confidence in IFR CIGs tonight. Breezy onshore winds
expected during the afternoon/evening today and again tomorrow. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR but some uncertainty remains as to
the timing of stratus return later today. The current TAF has
stratus returning between 04-06Z with IFR to LIFR ceilings
expected. At the same time, an otter eddy is developing in the
Monterey Bay this morning which may result in additional cloud
cover pushing into MRY/SNS early this afternoon. Confidence is low
that this will occur but it remains a possibility. Breezy onshore
winds are expected this afternoon/evening before winds weaken
overnight.

&&

.MARINE...
(Today through Friday)
Issued at 907 AM PDT Sun Aug 9 2026

Fresh to strong northwest winds persist with rough seas up to 12 
feet today through mid week. Northern coastal waters will be 
hazardous for small craft with occasional near gale force gusts 
possible through early week. The San Francisco Bay north of the 
Bay Bridge into the Delta will have gusty onshore winds through 
late evening. Long period southerly swells at around 15 to 17 
seconds continue.

&&

.FIRE WEATHER...
Issued at 1206 AM PDT Sun Aug 9 2026

Near-critical fire weather conditions persist today across the 
interior due to very hot and dry conditions. Strong thermal 
belting, extended burn periods, elevated PIG, and near or record 
BI/ERC values are expected. Temperatures will be 10 to 15 degrees 
above normal with a compressed marine layer. Poor minimum daytime 
relative humidity as low as 10% in the afternoons with little-to-
no recovery overnight is expected with nocturnal drying in the 
highest terrain. Even with critically dry conditions, wind is the 
limiting factor preventing this from being a Fire Weather 
Watch/Red Flag Warning event. Outside of the diurnal sea breeze 
that will bring breezy conditions in the afternoons and evenings 
through gaps and passes, onshore flow will be light. Additionally,
critical conditions are not expected to meet coverage or duration
requirements to warrant a product. Localized elevated fire 
weather conditions in the highest terrain can be expected Monday 
due to the combination of recent hot/dry conditions and the 
increase in onshore flow. Depending how the pattern and marine 
layer evolves, a headline may be warranted and this could last 
through Wednesday.

Sarment

&&

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

     Heat Advisory until 10 PM PDT this evening for CAZ503-504-510-
     512>518.

PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of 
     Bay Bridge.

     Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt 
     Reyes 0-10 nm.

     Small Craft Advisory until 9 PM PDT Monday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Kennedy
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Sun Aug 9 14:30:03 PDT 2026