850
FXUS66 KMTR 312304
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
404 PM PDT Sun Aug 31 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 144 PM PDT Sun Aug 31 2025

 - Moderate risk for heat-related illnesses through Monday

 - Elevated fire weather concerns across the interior mountains
   into Monday with low RH and moderate onshore winds each
   afternoon

 - Hazardous coastal conditions through Monday night due to long
   period southerly swell

&&

.SHORT TERM...
Issued at 144 PM PDT Sun Aug 31 2025
(This evening through Monday)

Mostly clear skies across the region this afternoon with a few high
level clouds streaming in from the southwest. This is as high
pressure over the Desert Southwest continues to nudge into
California resulting in warm to hot temperatures across the
interior. Meanwhile, mid/upper level low pressure persists of off
the Pacific Northwest coast.

For tonight, looking like only coastal areas have a chance at seeing
low clouds developing early Monday morning as the warm/dry air mass
aloft continues to keep the marine layer compressed to between 250-
500 feet. Thus, another mild night is expected with temperatures
dropping into the 50s to lower 60s (interior valleys). However,
warmer and drier conditions will prevail above the shallow marine
layer and only cool into the upper 60s to near 80 degrees F.

On Monday afternoon, expected similar temperatures as today with the
interior reaching Moderate HeatRisk while coastal areas remain
cooler.

Some tips to avoid heat-related illnesses include:

* Stay hydrated and drink plenty of fluids.
* Wear lightweight, light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.

&&

.LONG TERM...
Issued at 144 PM PDT Sun Aug 31 2025
(Monday night through next Saturday)

Monday night into Tuesday a weak cut-off low pressure will approach
from the southwest and become absorbed in the trough of off the
Pacific Northwest coast. This is when we have a non-zero chance of
high-based convection across the North Bay, East Bay and San
Francisco Bay Area. MUCAPE values range between 250-500 J/kg during
this timeframe. However, it appears the limiting factor will be the
available moisture in the 700-500 MB profile aloft. There is the
potential for this trough to result in coastal drizzle late Monday
night into Tuesday morning and again the following night.

A cooling trend will then persist from Wednesday into next weekend
as the marine layer deepens resulting in more widespread night and
morning low clouds.

&&

.AVIATION...
(00Z TAFS)
Issued at 356 PM PDT Sun Aug 31 2025

Currently VFR at all terminals with a few high clouds beginning to
filter in from a low pressure system over the Eastern Pacific Ocean.
With the exception of the coastal terminals of HAF, MRY, and SNS,
high confidence in VFR through the TAF period. If ceilings were to
develop, they would likely be low, thin, and brief as the region
remains under the influence of the upper-level shortwave ridge and
thus, subsidence/sinking air.

Vicinity of SFO...Currently VFR with westerly flow. High confidence
in VFR and westerly flow prevailing through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with northwesterly flow at
MRY and VFR with westerly flow at SNS. Low to moderate confidence on
the return of sub-VFR ceilings to the terminals tonight. Higher
confidence in MRY than SNS and if a ceiling were to develop, it
would likely be low, thin, and brief.

&&

.MARINE...
(Tonight through next Friday)
Issued at 238 PM PDT Sun Aug 31 2025

Fresh to strong northwesterly breezes will prevail through Monday,
posing hazardous conditions for small craft across much of the
waters. Northwesterly breezes will slowly diminish Tuesday through
Thursday to become moderate to fresh. Moderate seas will prevail
through Thursday.

&&

.FIRE WEATHER...
Issued at 129 AM PDT Sun Aug 31 2025

Warm and dry conditions will continue today and Monday, especially
for locations above 500ft. Widespread MinRH values between 10%-20%
combined with occasional wind gusts up to 30 MPH will result in
elevated fire weather concerns. We are also monitoring the potential
for elevated thunderstorms Monday afternoon into Tuesday. Chances
are low at the moment, but if the pattern evolves with improved
timing of the mid-level moisture and best lift associated with the
upper level disturbance we could see some isolated convection across
portions of the Bay Area, East Bay Hills and North Bay.

&&

.BEACHES...
Issued at 238 PM PDT Sun Aug 31 2025

Hazardous beach conditions will continue through tomorrow due to
long period (18 seconds) southerly/southwesterly swell causing an
increased risk for sneaker waves and rip currents along southwest
facing beaches, including but not limited to: Stinson Beach,
Santa Cruz Boardwalk Beach, and Twin Lakes Beach. Sneaker waves
can unexpectedly run significantly farther up the beach than
normal, including over rocks and jetties. Rip currents are
typically more frequent and stronger in the vicinity of jetties,
inlets, and piers. It is always important, but especially so on a
warm, dry, holiday weekend, to exercise caution while at the
beach. Never turn your back on the ocean, remain out of the water
to avoid hazardous swimming conditions, keep pets on a leash, and
wear a life jacket.

Sarment

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Monday evening for CAZ505-509-
     529.

PZ...Small Craft Advisory until 9 PM PDT this evening for Mry Bay.

     Small Craft Advisory until 3 AM PDT Tuesday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory until 3 AM PDT Monday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory until 9 PM PDT Monday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Sarment
MARINE...Sarment

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