761
FXUS66 KMTR 032050
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
150 PM PDT Thu Jul 3 2025

...New KEY MESSAGES, SHORT TERM, LONG TERM, FIRE WEATHER...

.KEY MESSAGES...
Updated at 135 PM PDT Thu Jul 3 2025

 - Elevated fire weather concerns persist through Friday for the
   East Bay and Santa Cruz Mountains.

 - Northwest winds of 30 to 55 mph through Friday across gaps,
   passes, and some valleys.

 - Near normal temperatures with slightly below normal through the
   weekend with a gradual warming trend next week.

&&

.SHORT TERM...
Issued at 135 PM PDT Thu Jul 3 2025
(This evening through Friday)

The forecast is on track early this afternoon with onshore flow
continuing this afternoon. The SFO-SAC MSLP "gradient" continues
to increase as diabatic heating induces surface pressure falls
across the Central Valley. In addition, larger scale synoptic
scale forcing in the form of an upper trough continues to
encourage onshore flow. In response, areas across the East Bay,
the San Bruno Gap and Salinas Valley are experiencing wind gusts
averaging between 25 mph and 45 mph. Short term hi-res guidance
such as the 2km PG&E WRF along with our in house WRF indicate that
gusts as great as 55 mph are still within the realm possibility
this afternoon. We`ll continue to advertise an elevated to near-
critical fire weather threat across the area this afternoon as a
few sites have seen RH fall down to near or below 15%. The
isolated nature of these "dry" sites precludes a Red Flag Warning,
however, we`ll continue to advertise/promote fire safety via
partner discussions as well as via our web page and social media.


Winds will continue through the evening hours and the airmass
across some of the elevated regions of the East Bay will likely
not decouple. This will translate to winds remaining elevated.
The 12Z OAK RAOB showed the moist layer beneath the inversion (the
marine layer) was around 1200 ft AGL. Forecast cross-sections
show the marine layer compressing further to around 1000 ft AGL in
the wake of the aforementioned upper trough (slight shortwave
ridging). This will translate to overnight RH recovery below 50%
for the higher terrain across parts of the Santa Cruz Mountains,
the Diablo and Santa Lucia Ranges.

With the loss of the upper trough, onshore flow and an
approaching diffuse frontal boundary (albeit weakening) may loosen
up the surface gradient some on Friday. In fact the PG&E WRF, the
MTRWRF and higher-end NBM probabilities indicate reduced flow as
a whole during the afternoon hours. While the lack of upper
support may take the edge off of the wind, the Central Valley
will still warm up quickly. This should continue to drive an MSLP
difference and thus diurnal onshore breezes. There will remain an
enhancement of the wind field across gaps, passes, and valleys
with gusts still as great as 45 to 50 mph. Afternoon RH will
still dip down between 15 and 25 percent, and that`ll necessitate
another round of an elevated to near critical fire weather threat.
This will be particularly true, given the potential for
additional ignitions given the holiday weekend. Please be mindful
of your outdoor activities and obey any local burn/fire
restrictions.


&&

.LONG TERM...
Issued at 135 PM PDT Thu Jul 3 2025
(Friday night through next Wednesday)

Not to sound like a broken record, but please be mindful of your
outdoor activities and obey any local burn/fire restrictions on
Friday evening given the dry grasses and brush.

With winds offshore abating some, we`ll likely see upwelling of
colder Pacific Ocean waters setting the stage for the development
of a thick deck of marine layer stratus. The diurnal pressure
gradient should support advection of the marine stratus into the
coastal regions this weekend. The marine layer is forecast to
thicken some up to around 1500 ft this weekend which fits our
climatological pattern ("No Sky July"), particularly along the
coast. The Extreme Forecast Index (from the EFI) suggests that the
EPS mean forecast is cooler than the model climate along the
coast and this increases confidence in a marine layer intrusion.
NBM temperatures seem reasonable, but we may need to make some
alterations to MaxTs on Saturday and Sunday.

Next week will be characterize by a gradual warming trend. The
global guidance indicates that the progression of the ridge will
be impeded by a developing cutoff upper trough that spawning from
the zonal flow across the Pacific Northwest. Both the 12Z
GFS/ECMWF advertise this feature in addition to the 00Z Cluster
Analysis through at least the middle of next week. This translates
to predominantly onshore flow until the SW US ridge attempts to
build. When/how that happens yields a high degree of forecast
uncertainty. EFI also seemed a bit underwhelming (and quite
negative) for MaxT/MinT through next week, though this is likely
biased by the cooler conditions along the coast. Examining the
850mb temperatures with respect to the SPC Sounding Climatology at
Oakland and Vandenberg and forecast mean values would place them
roughly around the 75th percentile for both areas. The 850mb
temperature forecast exhibited a high degree of spread (especially
in the GFS ensemble), so there`s still an opportunity for things
to be warmer or colder than forecast. What does appear most
certain is that the warmest locations (perhaps with isolated
pockets of `Moderate` HeatRisk) across the Bay Area and Central
Coast Wednesday onward will be across the southern Salinas Valley,
as well as across interior sections of the North Bay, East Bay,
and South Bay. Stay tuned for details.

&&

.AVIATION...
(18Z TAFS)
Issued at 1012 AM PDT Thu Jul 3 2025

IFR to MVFR conditions currently at the Monterey Bay terminals and
coastal spots such as HAF. Low ceilings are forecast to gradually
scatter out and lift through the morning and early afternoon.
However, coastal locations such as MRY and HAF have a greater
probability of IFR/MVFR ceilings to persist throughout much of the
day. Onshore winds increase this afternoon, stronger than previous
days!

Vicinity of SFO...VFR. High confidence for a windy day with gusts
expected to reach or exceed 35 kt at the terminal. Winds ease
slightly after sunset yet remain out of the west to northwest into
Friday. Low confidence for MVFR ceilings to return early Friday
morning, OAK would be mostly likely if any do develop. Any low
clouds that do develop will scatter out and/or lift by around 16Z
Friday with increasing onshore winds.

SFO Bridge Approach...Moderate to high confidence for VFR
conditions over the approach through the forecast period.

Monterey Bay Terminals...Currently IFR to MVFR forecast to lift to
MVFR to VFR by late morning or early afternoon. West to northwest
winds increase this afternoon with gusts up to 25 kt at SNS, before
easing after sunset. High confidence for IFR to MVFR to return late
this evening and potentially lowering to LIFR early Friday
morning.

&&

.MARINE...
(Today through Tuesday)
Issued at 424 AM PDT Thu Jul 3 2025

Gusty northwesterly winds and rough seas will continue through
late today. Gale force gusts will be likely across northern waters
through today. Winds easing by early next week. A low-amplitude
long period southerly swell will arrive today and persist through
Friday.

&&

.FIRE WEATHER...
Issued at 135 PM PDT Thu Jul 3 2025

An elevated to near critical fire weather threat will persist
this afternoon and again on Friday. Grasses and finer fuels remain
cured and available, and given the potential for new ignitions
due to the holiday weekend, an increase in initial attack type
activity should be expected by local fire personnel. Less
favorable burn conditions are anticipated this weekend as the
marine layer deepens and invades parts of the area. However, far
interior portions of the Bay Area and Central Coast, as well as
regions above 1500-2000 feet may still remain within an airmass
characterized by near-critical humidity and winds where there may
remain some potential for fire spread/growth.


&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT this evening for Mry Bay-SF
     Bay N of Bay Bridge.

     Small Craft Advisory from 3 PM to 9 PM PDT Friday for Mry Bay-SF
     Bay N of Bay Bridge.

     Gale Warning until 9 PM PDT this evening for Pt Arena to Pt
     Reyes 0-10 nm.

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

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

     Small Craft Advisory from 9 AM Friday to 3 AM PDT Saturday for
     Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 PM PDT this afternoon for Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

     Gale Warning until 3 AM PDT Saturday for Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Gale Warning until 3 PM PDT this afternoon for Pt Arena to Pt
     Reyes 10-60 NM.

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

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...RGass
MARINE...RGass
FIRE WEATHER...Bain

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