FXUS66 KMTR 110801
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
101 AM PDT Mon May 11 2026

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

.KEY MESSAGES...
Updated at 1 AM PDT Mon May 11 2026

 - Warming and drying trend will continue through Monday

 - Moderate risk for heat-related illnesses for sensitive 
   populations across the interior East Bay on Monday

 - Gradual cooling trend and unsettled weather midweek through 
   late week

&&

.SHORT TERM...
Issued at 1226 AM PDT Mon May 11 2026
(Today and tonight)

Upper level ridge still remains locked over CA, but that will
change after today. Let's first take a look at the marine layer 
situation. Similar to yesterday we still have a marine layer. You
can definitely tell there's a ridge overhead due to compressed
nature and discontinuous coverage of the stratus. Satellite fog 
product does show decent coverage along most of the coast, but
inland coverage is lacking and less than 24 hours ago. Expect some
additional expansion through sunrise. Will need to rely on the
building May sun angle to help erode the stratus by this
afternoon. Not much surface forcing to get rid of it. Regardless,
today will be the peak of our little warm spell. 850 mb temps are
still on track to be 20-22C, which under ideal conditions would 
yield max temps in the mid 90s. However, we still have some marine
layer influence. The last three days NBM guidance was just too 
warm across the interior and think today will be the same. Did 
shave a few degrees from the NBM for today. Max Temps will be in 
the 60s to 70s coast and bays and 80s to mid 90s far interior. The
slight downward trend on temps has now kept Moderate HeatRisk 
confined mainly to the East Bay interior valleys. 


By tonight the ridge shifts eastward and gets replaced by an
approaching upstream trough. As such, 500 mb heights begin to 
fall and the airmass cools. The marine layer will develop again
and with the exiting ridge coverage will be more and deeper.


&&

.LONG TERM...
Issued at 1226 AM PDT Mon May 11 2026
(Tuesday through Sunday)

Tuesday will be a transition day as the ridge is to the east and 
a cut-off low develop off the NorCal coast. Deeper marine layer 
to start the day and cooling airmass will lead to cooler 
temperatures with no HeatRisk concerns. Temps will still be still 
above normal, but trending toward seasonal averages. 

There was more uncertainty regarding the longwave pattern 
midweek, but the latest cluster run and ensemble guidance has 
given a more clear picture. The cut-off low from Tuesday night 
deepens and then sweeps through NorCal - taking the more northern 
track. So wait does that mean? Will still have some light rain 
and/or drizzle in the forecast for the N Bay/ SF/ SF Peninsula 
late Tuesday night through early Wednesday. Not expecting much in 
the way of accum. Higher confidence this passing low will bring 
temps back to seasonal averages. 

Zonal flow then develops for the rest of the work week into next
weekend with dry conditions and moderating temps.


&&

.AVIATION...
(06Z TAFS)
Issued at 950 PM PDT Sun May 10 2026

No major changes to the forecast with this TAF package. Tonight's 
observations include Mainly VFR conditions with the exception being 
along the San Francisco Peninsula and Monterey coastlines where 
sites are reporting MVFR to IFR cigs. These will likely hold and 
even build for the overnight hours bringing MVFR to IFR ceilings. 
The marine layer is expected to be around 1000ft tonight which means 
the onset of stratus in the valleys will be delayed or non-existent. 
Most sites have hints of cigs, with them lifting by mid to late 
morning. VFR conditions are expected for the majority of the region 
by Monday afternoon. The marine layer looks to return again tomorrow 
evening, opted to hint or fully bring it in for terminals near the 
coast. Medium to high confidence in the forecast.

Vicinity of SFO...Westerly winds are winding down and will fall to 
around  10kt or less after 6Z. The challenge outside of winds is the 
stratus. Satellite imagery and webcams show stratus building around 
the San Francisco Peninsula and slowly filtering into the western 
portion of KSFO's range ring. With the marine layer expected to be 
around 1000ft again, we should see the return of stratus tonight. 
Kept the pessimism in the TAFs with IFR cigs based on the last few 
nights, but time will tell if go that low or stay in the MVFR 
category. Stratus looks to dissipate mid to late morning, with 
breezy westerlies of 10-15kt returning Monday afternoon. The marine 
layer looks to return Monday night into Tuesday morning, which was 
brought into the latest TAF. Medium confidence in the forecast. 

SFO Bridge Approach...Similar to SFO. 

Monterey Bay Terminals...A small band of stratus remains around the 
Monterey Peninsula, which has been brought IFR cigs to KMRY. Expect 
this to build back in this evening bringing MVFR to IFR cigs to the 
terminals. Stratus should begin to erode by mid to late morning, 
though a few clouds could linger around KMRY for the afternoon. 
Stratus and low cigs look to return Monday evening. 

&&

.MARINE...
(Tonight through next Saturday)
Issued at 845 PM PDT Sun May 10 2026

Moderate seas and a fresh to strong northwest breeze with
isolated near gale force gusts continuing through tonight. Winds
ease late tonight across the inner waters then across the outer
waters tomorrow becoming a moderate to fresh northwest breeze.
Seas subside in response, but remain moderate with 4 to 5 foot
seas by mid week.Locally gusty conditions are likely across the
San Pablo and San Francisco Bays where terrain promotes wind
funneling. Winds increase and seas build again late Wednesday into
Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for Pt 
     Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena 
     to Pt Reyes 10-60 NM.

     Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt 
     to Pt Pinos 10-60 NM.

&&

$$

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

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Prepared by Boulder-Creek.com Weather at: Mon May 11 02:30:03 PDT 2026