722
FXUS66 KMTR 302303
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
403 PM PDT Sat Aug 30 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1244 PM PDT Sat Aug 30 2025

 - Moderate risk for heat-related illnesses through the middle of
   next week

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

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

&&

.SHORT TERM...
Issued at 1244 PM PDT Sat Aug 30 2025
(This evening through Sunday)

Sunny sky conditions prevail over the region this afternoon, with
patches of stratus off of the North Bay coast. This is as high
pressure to our east continues to build over the San Francisco Bay
Area and Central Coast. Moderate HeatRisk becomes more widespread
across the interior today with temperatures forecast to be in the
90s across and up to 105 degrees F in areas such as Bradley, Byron,
Pinnacles National Park, and Lake Berryessa. A shallow marine layer
and lack of offshore flow will keep conditions cooler near the coast
and bays. These temperatures will be around 5 to 15 degrees above
seasonal averages. Once again, breezy onshore winds are expected
this afternoon and evening before diminishing after sunset.

Tonight, seeing less indication for stratus to return overnight
with low 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.

With little change in the upper level pattern, similar conditions
are expected on Sunday as today. Please see the FIRE WEATHER and
BEACHES sections below for additional details.

&&

.LONG TERM...
Issued at 1244 PM PDT Sat Aug 30 2025
(Sunday night through next Friday)

In the extended, we are keeping an eye on Tuesday for the possibility
of high-based convection. At this time, the North Bay looks to be
the main focus with MUCAPE values approaching 250-500 J/kg. However,
the limiting factor may be the available moisture between 700-500 MB.
We will be sure to keep a close eye on this as we move closer to
Tuesday.

From the previous forecaster: "The upper level ridging remains
remarkably stable through the middle of the week, keeping Moderate
HeatRisk in place and high temperatures close to the those seen
today through Wednesday. Depending on how the forecast evolves, heat
products may need to be issued as we go through the next couple of
days. Towards the end of the 7-day forecast, the ridge doesn`t
really go away, so much as it erodes, with temperatures gradually
dropping closer to, or slightly below, the seasonal average. CPC
outlooks show a lean towards temperatures above seasonal averages
into the second week of September, but equal chances of temperature
above or below seasonal averages into the second half of the
month."

&&

.AVIATION...
(00Z TAFS)
Issued at 401 PM PDT Sat Aug 30 2025

Currently VFR at all terminals with not a cloud in the sky. High
confidence in VFR through the TAF period as the pattern will change
very little from the previous 24 hours. As the region remains under
the influence of the upper-level shortwave ridge, stagnant, sinking
air will facilitate an environment where haze and smoke from nearby
wildfires will not be able to mix out. As such, expect reduced slant
range visibilities.

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 westerly flow at MRY and
VFR with northwesterly flow at SNS. High confidence on VFR
and onshore flow prevailing through the TAF period.

&&

.MARINE...
(Tonight through next Thursday)
Issued at 401 PM PDT Sat Aug 30 2025

Winds across the waters have become breezy and gusty and will
continue through the weekend with gradually increasing wave
heights. The gusty winds and choppy seas will create hazardous
conditions across our coastal waters through the weekend into the
beginning of the next work week.

&&

.FIRE WEATHER...
Issued at 1244 PM PDT Sat Aug 30 2025

The marine layer has compressed to between 250-500 feet in depth
this morning and will likely remain that way into early next week.
Thus, warm and dry conditions will continue above 500-1,000 feet as
high pressure dominates the weather pattern aloft. Minimum relative
humidity values will be as low as the teens with maximum values
reaching into the 30% range in the highest elevations. Although we
are not expecting a long duration wind event and offshore winds are
not anticipated, breezy onshore winds will increase each afternoon
resulting in elevated fire weather conditions across the higher
terrain and far interior with gusts reaching 20-30 mph.

From previous forecaster: "Energy release component (ERC) forecasts
continue to show values above seasonal averages across most of the
region through the next week, which corresponds to a higher risk of
large fires starting and spreading through the week. One additional
factor will enhance the fire weather concerns through the weekend,
namely elevated human activity in the wildland areas as a result of
the Labor Day holiday weekend."

We are keeping a close eye on monsoon moisture wrapping around the
high pressure over the Desert Southwest and approaching cut-off low
from our southwest. On Tuesday, we are forecasting MUCAPE values to
reach 250-500 J/kg across much of the North Bay. However, the
limiting factor may be the available moisture between 700-500 MB.
Thus, there is a non-zero chance for high-based convection on
Tuesday. We will be sure to keep a close eye on this as we approach
early next week.

RGass/DialH

&&

.BEACHES...
Issued at 1244 PM PDT Sat Aug 30 2025

Long-period (15-18 seconds) south-southwest swell originating from
previous Tropical Storm Juliette is currently impacting our
coastline. This will continue to do so through Monday night,
creating an elevated risk for sneaker waves, rip currents, and rough
surf. This will be especially so at southwest facing beaches
including but not limited to Stinson Beach, Santa Cruz Boardwalk
Beach and Twin Lakes Beach. The potential exposure to the dangers
will be enhanced by the Labor Day holiday weekend as folks flock to
the coast to escape the hot temperatures across the interior.

RGass/Murdock

&&

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

PZ...Small Craft Advisory from 3 PM to 9 PM PDT Sunday for Mry Bay.

     Small Craft Advisory until 3 AM PDT Monday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt
     Reyes 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM Sunday to 3 AM PDT Monday for Pt
     Reyes to Pigeon Pt 0-10 nm.

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

&&

$$

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

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