611
FXUS66 KMTR 182149
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
249 PM PDT Mon Aug 18 2025

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

.KEY MESSAGES...
Updated at 245 PM PDT Mon Aug 18 2025

 - Warming trend into the weekend

 - Moderate HeatRisk for the interior Thursday-Saturday

 - See Heat Safety tips below

&&

.SHORT TERM...
Issued at 245 PM PDT Mon Aug 18 2025
(This evening through Tuesday)

Clear skies and warmer temperatures than we`ve seen the past couple
of days have made for a beautiful day across our area. A weak fetch
of offshore flow today across portions of the Central Coast has
resulted in a bump in daytime highs through the Salinas Valley and
Monterey Peninsula. Low stratus has eroded and should make for a
wonderful sunset up and down our coastline later this evening. A
compressed marine layer will limit stratus coverage during the
overnight into early Tuesday morning, keeping it mostly confined
to the immediate coastline where stratus does develop. It should
be a great night to watch the sunset, followed by the Perseid
meteor shower.

&&

.LONG TERM...
Issued at 245 PM PDT Mon Aug 18 2025
(Tuesday night through next Sunday)

A gradual warmup for the first half of the work week will accelerate
for Thursday and Friday, and then gradually ease into the weekend. A
building dome of high pressure will begin to center around the Four
Corners area Tuesday, then expand westward for the second half of
the work week. Consensus in the synoptic pattern is good through
Friday, providing high confidence for areas of Moderate HeatRisk
across much of our interior Thursday through Saturday. Consensus in
deterministic guidance begins to breakdown for the weekend into the
beginning of next week. It is too soon to know whether the
persistent troughing to our west that we`ve seen most of the summer
will win out over the expanding ridge as we head into the weekend
and into the beginning of next week. If the ridging becomes the
dominant synoptic influence we may see a longer period of Moderate
HeatRisk through the extended forecast, which would have
compounding impacts. Now is the time to begin to be aware and
prepare for upcoming heat impacts.

Heat Safety Tips:

Heat is the number 1 weather related killer in the United States.
Follow these tips to protect yourself, your loved ones, and your
animals.

-Stay inside in an air conditioned environment between 10am and 7pm.
-Suspend unnecessary outdoor activities during moderate heat, but
 if you must be outdoors, take frequent breaks in the shade or AC
 and drink cool water.
-Know the signs and symptoms of Heat Exhaustion vs. Heat Stroke!
Heat Stroke can be deadly if not treated immediately by a medical
professional. Call 911 if you suspect someone is suffering from Heat
Stroke.
-Wear a life jacket, swim near a lifeguard, and check conditions
before entering the water if going to a river or ocean to cool off.
Rivers and the ocean are extremely cold, and Cold Water Shock can
turn into paralysis and drowning if you are not careful.
-Use a cool and damp towel on your body if you do not have AC and
are feeling hot. Or, take a cool shower or bath.
-Do not leave kids or pets in a parked car.
-Ensure pets and livestock have access to shade and water.

&&

.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 until 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 until 3 AM PDT Tuesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Flynn
MARINE...Flynn

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