FXUS66 KMTR 181209
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
509 AM PDT Thu Jun 18 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1245 AM PDT Thu Jun 18 2026
- Hazardous beach conditions with increased risk of sneaker
waves and strong rip currents.
- Minor HeatRisk through the end of the week with temperatures
decreasing to below normal.
- Warming temperatures early next week with Moderate HeatRisk
concerns by midweek in interior locations.
&&
.SHORT TERM...
Issued at 1245 AM PDT Thu Jun 18 2026
(Today and tonight)
Satellite imagery early this morning indicates low clouds
expanding within a 1500-2000 ft deep marine layer, which is
slightly deeper than the past couple of days. The stratus will
follow a typical pattern today, continuing to expand in coverage
early this morning and then decreasing after sunrise before
retreating back to near the coast during the afternoon. Patchy
drizzle will also develop along the coast this morning. The flow
will remain onshore today and increase slightly from yesterday.
Winds will be breezy this afternoon and evening, especially near
SF Bay and Monterey Bay as well as adjacent valleys where gusts
should locally reach 20-30 mph. The marine layer and onshore winds
will keep temperatures similar or a degree or two cooler near the
coast today, with highs ranging from the upper 50s to around 70
degrees, generally slightly below normal. An approaching trough
will further reduce temperatures inland, decreasing around 5
degrees on average from Wednesday. This will place highs in the
70s and 80s, or around 5-10 degrees below normal in most areas,
resulting in Minor HeatRisk. Tonight, expect stratus to fill back
in within the marine layer with patchy drizzle redeveloping along
the coast.
Additionally, north and east of our area, there will be enough
moisture and instability ahead of the trough for showers and
thunderstorms to develop. Weak elevated instability above the
stable marine layer will extend just far enough south into
northern Sonoma and Napa counties for a 5% chance of showers and
thunderstorms in these areas. Chances for showers/storms will be
even lower further to the south. The main takeaway is that while
the potential for shower/storm development is very low, we cannot
completely rule out an isolated shower or thunderstorm across
northern areas.
The long-period southerly swell will continue to bring a risk for
sneaker waves and strong rip currents, with a Beach Hazards
Statement out through late Friday night. See the BEACHES section
for more information, but the main takeaway is to never turn your
back to the ocean!
&&
.LONG TERM...
Issued at 1245 AM PDT Thu Jun 18 2026
(Friday through Wednesday)
The trough off the coast will begin to move onshore on Friday,
then linger over the area into the weekend. Weak elevated
instability across the north will keep a 5% chance of showers and
thunderstorms across northern Napa and Sonoma counties on Friday.
Otherwise, temperatures will continue to trend lower, especially
inland, on Friday as the marine layer deepens further and cooler
air arrives with the trough. Highs near the coast should remain in
the upper 50s to around 70 degrees, and inland should decrease
another 5 degrees or so. Temperatures in most areas will remain
similar on Saturday, but begin to increase inland by Sunday as
the trough weakens. Expect stratus each night/morning with patchy
coastal drizzle.
Ensembles remain in agreement that a ridge will build across the
West early next week. This will bring a warming trend, especially
inland, with some interior locations reaching the 90s once again
and Moderate HeatRisk concerns by midweek.
&&
.AVIATION...
(12Z TAFS)
Issued at 426 AM PDT Thu Jun 18 2026
The marine layer has deepened to around 2000ft and spread into all
terminals, with intermittent MVFR CIGs at SJC and LVK. Stratus
will begin to erode from interior sites by 15-16z, closer to
18-20z for coastal sites. Southwesterly wind gusts will develop
beginning around 20z for nearly all sites, with gusts around
25kts at times. Highest confidence for >25kts SFO and APC. Weaker
winds and a resurgence of marine layer stratus expected again
tonight generally after sunset, with similar depth and inland
spread as observed this morning. Confidence for a CIG for at least
an hour at LVK and SJC Friday morning are around 65-75%, with the
best chances being after 10z Fri.
Vicinity of SFO...Clouds struggled to make it into the terminal
overnight, and intermittent MVFR CIGs will be possible through
16-17z when clouds retreat back towards the coastline and VFR sets
in. Gusty onshore winds develop around 20z, with gusts around
22-25kt possible through the afternoon and evening. Low clouds
move back inland likely after 07z, with around a 70% chance of
MVFR CIGs at SFO by 09z. Bases expected to be right around 1500ft
MSL, although could be a bit higher.
SFO Bridge Approach...Marine stratus has finally push in, with
some clearing just south of SFO. Clouds are expected to erode by
18-19z, with VFR prevailing thereafter. Afternoon and evening
west-southwest gusts will be similar to that of SFO, with weaker
after 06z Fri. Stratus will filter back in around the same time
as SFO, 07-09z.
Vicinity of SJC and OAK...Intermittent MVFR CIGs at SJC with more
persistent stratus at OAK. Clouds will clear from south to north
in the bay this morning, generally beginning around 16z, with some
lingering stratus in the vicinity of OAK through 21z. Otherwise,
VFR conditions should prevail for the afternoon and evening.
Gusty west to northwest winds develop after 21z for both
locations, weakening by 06z. Low clouds move back into OAK around
the same time with bases around 1500ft MSL. Confidence in an MVFR
CIG at SJC is around 70% for Friday morning, although timing
looks to be significantly later, after 10z, with periods of
scattering out possible.
Monterey Bay Terminals...MVFR with bases around 1200-1500ft MSL
currently, expecting to clear around 19-21z. Northwesterly gusts
at SNS after 20z may prevent low stratus from clearing completely
(40% chance), with intermittent MVFR CIGs possible through the
afternoon. Either way, FEW-SCT stratus will linger near both
terminals likely into the evening. As low clouds push back inland
after 02z Fri, models keep clouds out of MRY for much of the
night. However, seeing how sufficiently it has filled in the past
few nights and given the deepening marine layer, have added MVFR
CIGs for MRY beginning 04z Fri with moderate confidence.
&&
.MARINE...
(Today through Tuesday)
Issued at 426 AM PDT Thu Jun 18 2026
Winds will increase this afternoon and early evening and once
again on Friday afternoon and early evening leading to hazardous
conditions for small crafts in the San Pablo Bay, San Francisco
Bay, Suisun Bay and Monterey Bay. Expect moderate chop along with
the increasing afternoon winds each day. Southwesterly swell with
light to moderate seas will continue into the weekend, with
moderate west to southwest winds across the outer waters.
&&
.BEACHES...
Issued at 156 PM PDT Wed Jun 17 2026
Long period southerly swell at around 15 to 17 seconds will persist
through early Saturday as energetic storms in the Southern
Hemisphere continue to affect the California coast, especially for
south and southwest facing beaches. Hazardous beach conditions
are advertised, specifically for moderate to steeply sloped
beaches along the Pacific Coast of the North Bay, San Mateo, Santa
Cruz counties. A Beach Hazards Statement for Pacific Coast
beaches continues through late Friday night. Be sure to check
beach conditions before you head out. Sneaker waves will run up
the beach much farther than other waves, potentially catching
beachgoers by surprise and resulting in people being swept into
the water. Rip currents are strong enough to pull the strongest
swimmers away from shore. Swim near a lifeguard if possible. Stay
back from the beach, and away from jetties, piers, beachside
rocks, and other infrastructure near the water. Never turn your
back to the ocean!
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through late Saturday night for CAZ006-
505-509-529-530.
Coastal Flood Advisory until 5 AM PDT early this morning for
CAZ006-506-508.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
evening for Mry Bay-SF Bay N of Bay Bridge.
Small Craft Advisory from 3 PM to 9 PM PDT Friday for Mry Bay-SF
Bay N of Bay Bridge.
&&
$$
SHORT TERM...Tangen
LONG TERM....Tangen
AVIATION...Zuber
MARINE...JM
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Prepared by Boulder-Creek.com Weather at: Thu Jun 18 08:30:02 PDT 2026
From the National Weather Service
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