639
FXUS66 KMTR 070448
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
948 PM PDT Sun Jul 6 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 129 PM PDT Sun Jul 6 2025

 - Moderate HeatRisk returns to portions of the Interior Bay Area
   and Central Coast Wednesday through next weekend.

 - Localized elevated fire weather conditions for the Bay Area and
   Central Coast Wednesday through next weekend.

 - Slight risk (20%-40%) of extreme heat for far interior portions
   of the Bay Area and Central Coast July 12th-14th.

&&

.UPDATE...
Issued at 715 PM PDT Sun Jul 6 2025

The marine layer stratus is beginning its nocturnal push inland
as the sun begins to set. By morning, the coverage should be
slightly more expansive than today as low pressure offshore
allows the marine layer to deepen. Cool and moist will be the
theme through Tuesday before a ridge builds and brings inland
temperatures above normal Wed-Fri. Thursday looks like the warmest
day, but with temperatures about 5 degrees above normal, we are
only expecting moderate HeatRisk in inland and higher elevation
areas within the North Bay, East Bay, South Bay and Monterey and
San Benito Counties. A cooling trend should bring temps back to
normal this weekend.

&&

.SHORT TERM...
Issued at 129 PM PDT Sun Jul 6 2025
(This evening through Tuesday)

An upper-level cutoff low off the Northern California Coast will be
the defining feature of the short term forecast. Sensible weather
will feature seasonably cool conditions and onshore winds with gusts
up to 35 mph through gaps and passes, across ridgelines, and down
the Salinas Valley. The marine layer is currently being observed at
1,800 feet on the Fort Ord profiler and will continue to deepen to
3,000 feet by Tuesday. This, in addition to the stratus presentation
currently, means that it will have no problem penetrating farther
inland tonight and continuing that trend tomorrow night. There is
also a slight (15%) chance for drizzle along the coast and over the
waters due to the lifting mechanism in place. Southerly transport
winds may (you guessed it) transport smoke in from the Madre Fire
that is burning in San Luis Obispo through Tuesday.

&&

.LONG TERM...
Issued at 129 PM PDT Sun Jul 6 2025
(Wednesday through next Saturday)

The pattern begins to change Wednesday as the upper-level cutoff low
becomes an open wave and gets nudged eastward by building broad high
pressure. This will kickoff the warming and drying trend with the
return of moderate HeatRisk and localized elevated fire weather
conditions. Fortunately, several rounds of upper-level shortwave
trough energy will help keep the ridge in check, not allowing the
axis or peak to enter our area. Global ensemble clusters are in
agreement with heights rising through Thursday with the ridge
showing signs of weakening, albeit slightly, Friday. This will
translate to Thursday being the warmest day of the week with
temperatures topping out at 10 degrees above normal with Friday
being slightly cooler. Global ensemble clusters diverge Saturday
with 51% in favor of heights rebuilding and 49% in favor of heights
falling, suggesting uncertainty in the forecast. The propagation
of what happens will be integral in the extended forecast as the
Climate Prediction Center (CPC) has highlighted the far interior
portions of the Bay Area and Central Coast with a slight (20%-40%)
chance of extreme heat July 12th-14th, thus it is intuitive to
believe that if the ridge has more time to build that we could be
dealing with hotter conditions and subsequently greater impacts
than what are currently being forecast. In terms of elevated fire
weather conditions, high pressure and the accompanying subsidence
aloft will compress the marine layer to 1,000 feet Wednesday
resulting in little inland intrusion and poor to moderate relative
humidity recovery above it. Additionally, light offshore flow is
expected in the higher terrain during the morning hours of
Wednesday and Thursday. Please exercise fire and heat safety,
especially coming off of a cool June.

&&

.AVIATION...
(06Z TAFS)
Issued at 937 PM PDT Sun Jul 6 2025

Marine layer holding steady around 1 kft going into the overnight
hours, and will persist into the morning hours. Most terminals
that get cigs overnight will likely see LIFR/IFR, and more likely
to be teetering IFR/MVFR around the SF Bay. Reasonably good
confidence in timing forecasts as clouds build in tonight, and
high confidence that stratus will hold on to much of the immediate
coastline through the day Monday. Breezy onshore flow during the
afternoons, nothing out of the ordinary in terms of wind.

Vicinity of SFO...Decent confidence in the timing of stratus
affecting the vicinity of the terminal, but less confidence if
persistent stratus will actually settle in over the airfield.
Slightly shallower marine layer allowing for some drying as air
descends the San Bruno Gap, so there is some uncertainty with how
much the northern part of the Bay will fill in. Otherwise, high
confidence in clearing time Monday morning, should cigs fill in
over the terminal.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...LIFR/IFR overnight tonight with
reasonable confidence in mid-morning clearing to VFR and mostly
SKC throughout the rest of Monday. Marine stratus expected to
return just after sunset. Earlier along the immediate coast.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 937 PM PDT Sun Jul 6 2025

Winds continue to diminish over the outer waters tonight. Gentle
to moderate breezes persist across the coastal and outer waters
through the middle of the week. Winds increase by the latter half
of the week with moderate to fresh breezes expected. Building seas
across the outer waters late in the week as a modest northwesterly
swell enters the picture around 9 to 10 feet at 9 seconds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Behringer
MARINE...Behringer

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