FXUS66 KMTR 201640
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
940 AM PDT Wed May 20 2026

...New UPDATE, MARINE...

.KEY MESSAGES...
Updated at 1036 PM PDT Tue May 19 2026

 - Diurnally driven winds, with onshore winds during the afternoon 
   and early evening.  

 - Above normal temperatures continue through midweek with seasonal 
   temperatures returning late week.

 - Warm and dry weather through Thursday leads to elevated fire
   weather concerns for the interior Bay Area and Central Coast. 

&&

.UPDATE...
Issued at 940 AM PDT Wed May 20 2026

Temperatures in the lower elevations are up to 10 degrees cooler 
compared to this time yesterday. This is thanks to a deeper marine 
layer in place and lack of stronger offshore winds. Thus, maximum 
temperatures may be cooler than yesterday as a result. However, very 
dry conditions will persist in the higher terrain generally above 
1,000 feet. 

RGass

&&

.SHORT TERM...
Issued at 1036 PM PDT Tue May 19 2026
(Tonight through Thursday)

Little change in the forecast as high pressure slowly creeps into 
Northern California today. Satellite imagery this evening shows 
high clouds sliding down the West Coast, with much of the Bay Area
likely seeing some cirrus. With the current data, temperatures 
look to be on track; however, if we're not able to get radiational 
cooling, our temperatures for tonight might be low/cool. This 
would be because the clouds act as blanket, allowing less heat to 
escape at night. It'll be something to keep an eye on over the 
next few hours. 

In terms of Wednesday, if you guessed, "No pattern change. Ha, this 
means another day of warmer weather", you'd be correct! A potential 
fly in the ointment is if the marine layer attempts to manifest 
around 500 feet. This might keep temperatures a few degrees cooler 
along the immediate coast, but elsewhere temperatures should be 
similar to Tuesday, perhaps a few degrees higher. 

&&

.LONG TERM...
Issued at 1036 PM PDT Tue May 19 2026
(Thursday night through next Tuesday)

No major changes to the extended forecast. Upper level troughing 
looks to keep hold over the western US, while the Pacific high 
pushes even more into northern California on Thursday. With the high 
being a bit more pronounced, another warm day will be on tap. 
After that, guidance has flow becoming quasi-zonal for a brief 
period before troughing returns on Friday. The marine layer looks 
to be around 500ft on Thursday, deepening to around 1000ft by 
Friday and then lasting through the weekend. With onshore flow, a 
deeper marine layer, and troughing through the weekend the NBM's 
temperatures are bit too warm. Opted to start trending towards 
slightly cooler temperatures given the ensembles and cluster 
analysis. But there is a chance ridging wins out and temperatures 
might warmer. Definitely something to keep an eye on over the next
few days.

&&

.AVIATION...
(12Z TAFS)
Issued at 503 AM PDT Wed May 20 2026

VFR at the big three this morning and expect that to continue
despite some stratus forming offshore. Guidance was a little too 
aggressive in bringing in stratus elsewhere and thus have cut 
back on stratus this morning. HAF and SNS are experiencing some 
hz/br drop the flight CAT. VFR this afternoon gusty onshore flow. 
Gusts 15-20kt seems reasonable. For tonight, marine layer 
currently off the coast will move locally inland with highest 
conf for HAF and MRY/SNS.

Vicinity of SFO...VFR. NW winds ramp up this afternoon with gusts
to 20kt.

SFO Bridge Approach...Similar to SFO. 

Monterey Bay Terminals...MRY is VFR, but enough low level moisture
is at SNS to have occasional br/hz. Much higher conf for stratus
intrusion tonight into Wednesday. 

&&

.MARINE...
(Today through Monday)
Issued at 940 AM PDT Wed May 20 2026

A weak frontal boundary to the north will maintain fresh to strong
northerly breezes and rough seas over the outer waters north of
Pigeon Point through early Thursday. Elsewhere, moderate to fresh
northerly breezes and moderate seas will prevail. Conditions
improve into the weekend as seas and northwesterly breezes become
moderate.

&&

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

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...MM
MARINE...RGass

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Prepared by Boulder-Creek.com Weather at: Wed May 20 10:30:02 PDT 2026