FXUS66 KMTR 111627
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
927 AM PDT Mon May 11 2026
...New UPDATE, MARINE...
.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
&&
.UPDATE...
Issued at 926 AM PDT Mon May 11 2026
The marine layer compressed overnight and early this morning to
around 1,000 feet in depth. This has resulted in earlier clearing
where stratus did develop and low clouds are highly likely to clear
to the coast by late morning or early afternoon. This will allow for
interior areas to warm into the mid 80s to lower 90s while coastal
locations stay in the upper 50s to mid 60s as high pressure over the
Desert Southwest continues to strengthen. No updates anticipated for
this morning as the forecast largely remains on track.
RGass
&&
.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...
(12Z TAFS)
Issued at 449 AM PDT Mon May 11 2026
Conditions are a mix of stratus and patchy fog /IFR-LIFR/ and
cirrus clouds /VFR/ over the forecast area. Patchy light drizzle
is possible this morning. Conditions improving to MVFR-VFR by late
morning or early afternoon. Areas of coastal stratus and fog /IFR-
LIFR/ move inland tonight and Tuesday morning.
Vicinity of SFO...Tempo /IFR/ in stratus 13z-16z this morning
otherwise VFR today. VFR tonight except stratus /IFR/ returns
08z Tuesday morning. West wind 5 to 15 knots.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus, fog and a few patches of light
drizzle /IFR-LIFR/ this morning. Conditions improving to MVFR-VFR
by late morning or early afternoon. Stratus, fog and possibly a
few patches of light drizzle /IFR-LIFR/ return tonight and Tuesday
morning. Mainly west to northwest winds 5 to 15 knots.
&&
.MARINE...
(Today through Saturday)
Issued at 926 AM PDT Mon May 11 2026
Winds have subsided everywhere except the far northern outer
waters where occasional strong gusts continue. A moderate to fresh
northwest breeze will continue over the waters through midweek.
Seas subside but remain moderate with 4 to 6 foot seas through
midweek. Winds increase and seas build starting mid-week with gale
force winds likely starting Friday and continuing through the
weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM to 9 PM PDT Tuesday for Pt Arena
to Pt Reyes 0-10 nm-SF Bay N of Bay Bridge.
Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Canepa
MARINE...Canepa
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Prepared by Boulder-Creek.com Weather at: Mon May 11 10:30:02 PDT 2026
From the National Weather Service
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