591
FXUS66 KMTR 012327
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
427 PM PDT Mon Sep 1 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1234 AM PDT Mon Sep 1 2025

 - Moderate risk for heat-related illnesses continues today,
   gradual cooling Tuesday through the remainder of the week

 - Elevated fire weather concerns today across the interior
   mountains with low RH and moderate onshore winds

 - Hazardous coastal conditions through tonight due to long period
   southerly swell

&&

.SHORT TERM...
Issued at 1256 PM PDT Mon Sep 1 2025
(This evening through Tuesday)

Today is forecast to be the last day with widespread Moderate
HeatRisk across the interior. The marine layer is at around 500 feet
in depth which has allowed for low level clouds to return to coastal
areas earlier this morning with these largely remaining intact. This
will keep conditions cooler than yesterday near the coast while the
interior heats up, generally in the 90s up to 102 degrees F in the
warmest interior spots. Meanwhile, a mid/upper level cut-off low
pressure just of of the Central Coast is forecast to shift to the
northeast.

As the upper level low approaches the North Bay tonight through
Tuesday evening, we will have a less than 10% chance of high based
convection across much of the Central Coast and Bay Area. This is as
MUCAPE values reach between 250-1000 J/kg. An increase in mid/upper
level monsoon is also forecast during this timeframe. However, the
limiting factor will be the available moisture between 500-700 MB.

Overnight temperatures drop into the 50s in most urban locations,
lower 60s in the interior valleys, and upper 60s to lower 80s in the
higher terrain. Temperatures cool on Tuesday, but remain 5-10
degrees above seasonal averages across the interior and in the
higher terrain.

&&

.LONG TERM...
Issued at 1256 PM PDT Mon Sep 1 2025
(Tuesday night through next Sunday)

A cooling trend is the forecast for the remainder of the week as
troughing develops off of the West Coast and the ridge of high
pressure shifts east. Thus, expecting the marine layer to deepen
result in more widespread stratus developing each evening and
spreading inland into the morning hours. Later in the forecast
period, the pattern aloft appears to become more active and
unsettled. Thus, the CPC has near to cooler than normal temperatures
and above average precipitation. Note: Above average precipitation
this time of year does not amount to much and may be in the form of
coastal drizzle and/or light rain. Thus, widespread rainfall is
not expected.

&&

.AVIATION...
(00Z TAFS)
Issued at 422 PM PDT Mon Sep 1 2025

Currently VFR at all terminals with stratus eroding off the coast. The
culprit of this seems to be a northerly (drying) gradient across
the state of California which supports dry air entraining into the
marine layer. Because of this, I have optimistically opted for
VFR at all terminals with the exception of the coastal terminals
of HAF, MRY, and SNS, and even then, confidence on the return of
LIFR ceilings is only moderate at best. There`s also a non-zero
chance for elevated convection beginning tonight. While I don`t
expect the ingredients to align and directly impact a terminal,
some rain showers may be seen in the air.

Vicinity of SFO...Currently VFR with westerly flow. High
confidence in VFR and westerly flow prevailing through the TAF
period. If a ceiling were to develop, it would likely be low, thin,
and brief.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with northwesterly flow at
both terminals. Moderate confidence on LIFR ceilings developing at
both terminals tonight with higher confidence in MRY than SNS. The
biggest question mark is if dry air will erode the marine layer this
far south or if moist northwesterly flow will win out. Westerly
winds will prevail through the TAF period.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 422 PM PDT Mon Sep 1 2025

Hazardous conditions for small crafts continue through early
Tuesday morning across the outer waters as a fresh to strong
northwesterly breeze prevails. Winds gradually diminish through
the rest of the day on Tuesday, becoming moderate to fresh, with
localized strong gusts possible across the northern outer waters
through midweek. Moderate seas continue through late week before
seas abate over the weekend.

&&

.FIRE WEATHER...
Issued at 1234 AM PDT Mon Sep 1 2025

Warm to hot and dry conditions will continue today, 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 later this afternoon into Tuesday.
Chances are low, 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, with cloud to ground
lightning and gusty winds the primary concern. Given the elevated
nature of the storms, if they develop, wetting rainfall is not
expected.

&&

.BEACHES...
Issued at 1234 AM PDT Mon Sep 1 2025

Hazardous beach conditions will continue through tonight 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 until 11 PM PDT this evening for CAZ505-
     509-529.

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

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

     Small Craft Advisory until 9 PM PDT Tuesday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

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

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