558
FXUS66 KMTR 181758
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1058 AM PDT Mon Aug 18 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 247 AM PDT Mon Aug 18 2025

 - Warming into the late week

 - Moderate heatrisk in the inland areas Thursday-Saturday

 - Slight cooling into the weekend, but still warm into the next
   work week

&&

.UPDATE...
Issued at 855 AM PDT Mon Aug 18 2025

Forecast is on track this morning. Visible satellite trend shows
low stratus eroding over the East Bay, and SF Peninsula, which
should continue until stratus is confined to the shoreline.
Farther south, expect sunny skies including coastal areas, and
warmer temperatures than yesterday.

&&

.SHORT TERM...
Issued at 247 AM PDT Mon Aug 18 2025
(Today and tonight)

Cloud cover is less widespread than previous nights, with still some
focus around the SF Bay for lingering low clouds, but clear
conditions for areas south of Half Moon Bay. Cloud cover for areas
not along the coast looks to burn off fairly quickly today. That,
along with a slight decrease in onshore flow, allows for slightly
warmer conditions than yesterday for all but the immediate coast.
Highs in the far interior look to peak in the low 90s, while the
coast and areas slightly inland mostly stick to the 60s and 70s.

Winds will also begin to back off today. Aside from the regularly
breezy passes and valleys, most of the region will begin to see
lighter winds that will last into the long term portion of the
forecast.

&&

.LONG TERM...
Issued at 247 AM PDT Mon Aug 18 2025
(Tuesday through Sunday)

The marine layer is compressing and winds will weaken as our upper
level pattern continues to build into a ridge into the work week. As
this ridge of high pressure builds, the interior areas will really
see the warming trend while the immediate coast and adjacent valleys
see only slight warming as the marine layer is set to compress, but
not completely erode.

A quick note about the coast: The astronomical set up will give us a
bit more movement in the tides into the  mid week. The high tides
will be higher and the low tides will be lower. This will get high
tide levels close to coastal flooding criteria, but not crossing the
threshold for coastal flood advisories. It`s still worth noting
because people may be heading to the SF Bay shoreline to beat the
heat in the next few days.

Meteorologist  Sarment, tonight`s marine forecaster, provided some
additional info:
"Localized minor coastal flooding will likely occur in Bayside Marin
County through Sunday, August 24th as high tides will remain in
excess of 6.0 feet. Coastal locations that are directly located next
to Richardson Bay such as Sausalito, Tam Valley, Manzanita, the
Sausalito-Mill Valley Bike Path, and the Manzanita Park N Ride can
expect nuisance flooding where typically dry land gets wet. Impacts
are expected to be minor at most - remember, do not drive around
barricades or through water of unknown depth."

Getting back to the heat and the interior: models continue to show a
peaking/plateauing of the warming trend by Thursday and Friday.
Highs look to break into the 100s for the far interior. Some
isolated areas in the Santa Lucias could break into the 110s due to
limited overnight cooling with as heat gets trapped in the thermal
belt in that mountain range. Luckily, these temps will not be
widespread, but heatrisk does become moderate for areas away from
the coast with 90s to low 100s possible. The coast, however looks to
be protected by a fairly shallow, but still intact marine layer,
keeping highs in the 60s and low 70s.

The biggest question in the longer term forecast continues to be how
long the heat persists. Confidence is increasing at small
improvements to onshore flow into the weekend, offering slightly
cooler temperatures Saturday and cooler still for Sunday. However,
models still keep us adjacent to the Ridge. They also don`t look to
break the ridge nor push it east until the middle of the next work
week. This could call for temperatures to remain on the warm side
well into the next work week.

&&

.AVIATION...
(18Z TAFS)
Issued at 1042 AM PDT Mon Aug 18 2025

Drier air has infiltrated the marine layer and low clouds have
retreated from all terminals. Most TAF sites will stay cloud free
through the next 24 hours, though there is some uncertainty around
the coastal sites. Otherwise moderate onshore wind is expected
this afternoon before decreasing overnight.

Vicinity of SFO...Will SFO get a ceiling tonight? That`s the big
question for the 18Z TAF. GFSLAMP stays clear but NAM-MOS brings
more than 6 hours of MVFR ceilings Tuesday morning. Looking at the
previous 24 hours of METARs shows MVFR ceiling were coming and
going through the night, with nearly 6 hours of IFR ceilings
earlier this morning. The difference is building high pressure
will compress the marine layer and should keep any stratus more
confined to the coast. Often in these situations the boundary
layer is too shallow for clouds to move over the San Bruno Gap,
and instead push through the Golden Gate. It that pattern
materializes, it actually brings a higher chance of ceilings to
OAK than SFO, as the clouds swirl around in the Bay. As such, I
decided to bring a period of BKN015 to OAK tomorrow morning, but
kept SFO VFR. I did add a SCT group to show the potential timing
and height if ceilings do manage to form over SFO (12-18Z 1,500
feet). Outside of cloud cover, there is high confidence that winds
will soon shift to WNW and increase to 15-20 kts through the
afternoon and evening before decreasing overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Clear skies will stick around through the
day with moderate onshore wind. There is a chance for ceilings to
form at both MRY and SNS, but confidence is too low to mention
explicitly. To demonstrate the potential timing and height at MRY,
I added a SCT004 group starting at 191200Z. While it`s possible,
the chances are lower at SNS, and I decided to keep that TAF one
line VFR.

&&

.MARINE...
(Today through Saturday)
Issued at 855 AM PDT Mon Aug 18 2025

Moderate NW breezes will prevail today with strong gusts along
the coastal jet regions of Point Reyes and Point Sur and across
the bays. As the pressure gradient tightens mid week, NW breezes
will increase to fresh with widespread hazardous conditions for
small craft across the waters by Wednesday. Moderate seas will
prevail through Wednesday, building to become rough for the outer
waters by Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-SF Bay N
     of Bay Bridge.

     Small Craft Advisory from 3 PM to 9 PM PDT Tuesday for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT
     Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Murdock
LONG TERM....Murdock
AVIATION...Flynn
MARINE...Flynn

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