Clayton, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

627
FXUS66 KMTR 092031
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
131 PM PDT Wed Jul 9 2025

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 130 PM PDT Wed Jul 9 2025

 - Minor to moderate HeatRisk for the Interior Bay Area and
Central Coast.

 - Localized elevated fire weather conditions for the Interior
Bay Area and Central Coast.

&&

.SHORT TERM...
Issued at 130 PM PDT Wed Jul 9 2025
(This evening through Thursday)

The warming trend kicks off today as as an area of broad high
pressure extending from the Desert Southwest to the Eastern Pacific
Ocean builds into place. Effects of this are already being observed
with locations outside of the marine layer influence observing
warmer conditions than what were observed 24 hours ago as well as
the marine layer compressing about 600 feet in 24 hours which is
indicative of subsidence aloft. Yet, temperatures will still remain
near to below normal for all but the highest terrain today. Fog will
return to coastal and valley locations tonight.

&&

.LONG TERM...
Issued at 130 PM PDT Wed Jul 9 2025
(Thursday night through next Tuesday)

Tomorrow will be the warmest day of the week with temperatures
peaking near 10 degrees above normal. Friday will be cooler for all
but the farthest interior portions of the area as the axis of the
longwave upper-level ridge moves inland. Global ensemble clusters
are in agreement of longwave ridging developing again Saturday over
the Eastern Pacific Ocean. This feature will likely build through
the weekend and move inland early next week. A stable pattern means
more or less the same daily forecast for the long term: interior
areas will get warm to hot with temperatures of 5-10 degrees above
normal, elevated fire weather conditions will persist for areas
above the marine layer with minimum daytime relative humidity of 20-
30% with little-to-no overnight recovery, onshore flow will be
realized with the diurnally driven afternoon sea breeze, and stratus
will come in every night for coastal and valley locations.

&&

.AVIATION...
(18Z TAFS)
Issued at 1108 AM PDT Wed Jul 9 2025

The ceilings are clearing out with mostly clear skies expected
through the afternoon. The exception is along the immediate coast,
where IFR-MVFR conditions are possible through the day. There is
a pattern shift ongoing today as high pressure becomes the
dominant feature and compresses the marine layer. This will cause
less expansive stratus coverage Thursday morning. On the other
hand ceilings and visibility will be lower for the terminals that
are close enough to the coast to remain in the marine layer.

Vicinity of SFO...The ceiling scattered out just before 18Z, and
VFR conditions are virtually guaranteed for the next several
hours. The uncertainty starts to increase around 03Z. The
persistence forecast would bring MVFR ceilings back at this time,
lowering to IFR later in the night. However, as the marine layer
compresses, the stratus won`t push inland as fast. With NW winds
in the boundary layer, it`s likely that the Peninsula hills will
help protect the terminal from an early ceiling return. By 12Z
Thursday morning, there is a 50-60% chance that SFO will develop a
ceiling. If so, the height will be close to the MVRF/IFR
threshold. In summary, the ceiling timing and height confidence
is low beyond the first 9 hours of the TAF.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals...With a compressing marine layer, MRY will
spend much longer under a ceiling than SNS over the next couple
days. With NW winds there is also a good chance for LIFR ceilings
and possibly fog development in the early morning.

&&

.MARINE...
(Today through Monday)
Issued at 1108 AM PDT Wed Jul 9 2025

As the gradient between high pressure in the East Pacific and
lower pressure over the Intermountain West increases, fresh to
strong NW winds will develop through the afternoon and evening.
These winds will maintain strength through Thursday, building
rough seas in the exposed waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Thursday for Pt Arena
     to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Flynn
MARINE...Flynn

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