041
FXUS66 KMTR 301155
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
455 AM PDT Sat Aug 30 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 129 AM 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
   this weekend 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 129 AM PDT Sat Aug 30 2025
(Today and tonight)

Satellite imagery reveals clear skies throughout most of the region,
with some patches of stratus in western Marin County and the
northern San Mateo Peninsula. Profiler observations have shown a
dramatic compression of the marine layer over the last six hours,
with the latest observations showing the top of the marine layer at
or below 500 feet. Assuming that this compression holds for the rest
of the night, any stratus development will generally be limited to
the coastal valleys, with low to moderate confidence in stratus
development in the Bay Area or the Salinas region. Low temperatures
range from the middle 50s to lower 60s in the lower elevations, to
the middle 60s to lower 70s in the higher elevations.

Today marks the first day of a string where Moderate HeatRisk is
expected for inland regions, as an upper level ridge builds across
the West Coast. This level of heat will bring a risk of heat-related
illnesses to vulnerable populations, including children, the
elderly, pregnant women, and people who are working or living
outdoors without adequate shelter or hydration. High temperatures
will range from the upper 80s to the triple digits in the inland
regions, or around 5 to 15 degrees above seasonal averages, while
the Bayshore sees highs in the middle 70s to lower 80s and the coast
sees highs in the middle to upper 60s. Some breezy onshore winds
will develop this afternoon and evening. In the interior mountains,
this will combine with hot and dry conditions to increase the fire
weather threat. See the FIRE WEATHER section for more information.
Finally, long period southwest swell from the remnants of Tropical
Storm Juliette will impact the coast beginning today, leading to
an elevated risk of rip currents and sneaker waves, especially
along southwest facing beaches. See the BEACHES section for more
information.

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 129 AM PDT Sat Aug 30 2025
(Sunday through Friday)

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...
(12Z TAFS)
Issued at 447 AM PDT Sat Aug 30 2025

VFR is expected to prevail through the forecast period. It has
been clear all night combined with the marine layer decreasing
from 1500ft Friday evening to about 900ft with the 12z balloon
launch. Any stratus that does develop should be limited in
coverage and confined to the coastline.

Vicinity of SFO...VFR is expected to prevail through the forecast
period. A drier airmass combined with compressed marine layer will
limit stratus development.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR is expected to prevail through the
forecast period. Similar to the Bay Area terminals, drier air and
compressed marine layer (~400ft combined to ~900ft near KOAK and
KSFO) will limit any stratus that does develop, to the coastline.

&&

.MARINE...
(Tonight through next Thursday)
Issued at 857 PM PDT Fri Aug 29 2025

Fresh to strong wind gusts are developing and look to last
through the holiday weekend along with 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 129 AM PDT Sat Aug 30 2025

A warming and drying trend continues through the weekend and the
early part of the upcoming week, with elevations above around 1000
feet seeing relative humidity values dropping into the teens during
the daytime. The marine layer has compressed rather noticeably this
evening, with profiler observations suggesting that the marine layer
inversion starts at around 500 feet or below. As a result, the
higher elevations will not see much relief overnight as poor
humidity recoveries and warm morning lows persist. Although we are
not anticipating a long duration wind event, breezy onshore winds
each afternoon will elevate the fire weather threat in the inland
mountains, particularly favored gaps and passes where gusts could
reach 20-30 mph, 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.

&&

.BEACHES...
Issued at 125 PM PDT Fri Aug 29 2025

Long-period (15-18 seconds) south-southwest swell originating from
previous Tropical Storm Juliette will impact the coast Saturday
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 inland
temperatures across the interior.

&&

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

PZ...Small Craft Advisory from 9 AM this morning to 3 AM PDT Monday
     for Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Monday
     for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-
     60 NM-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-
     10 nm.

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

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...JM
MARINE...JM

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