Clayton, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

354
FXUS66 KMTR 200435
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
935 PM PDT Thu Jun 19 2025

...New AVIATION...

.SYNOPSIS...
Issued at 202 PM PDT Thu Jun 19 2025

Temperatures below seasonal averages persist through the weekend.
Gusty winds and low daytime humidities lead to elevated fire weather
conditions in the interior. Seasonal conditions resume early next
week.

&&

.UPDATE...
Issued at 906 PM PDT Thu Jun 19 2025

We recorded much cooler high temperatures across the more inland
areas today. It was around 5-10 degrees cooler for the North Bay
Valleys, San Jose, and interior Monterey Co. The biggest departures
included Concord, Redwood City, and Livermore all of which were
around 20 degrees cooler as the onshore flow increased today.

In spite of these cooler conditions, humidities away from the coast
only saw small improvements. That, mixed with our stronger winds
still keeps the interior (specifically the higher elevations) in
fire weather danger. Luckily, the humidities continue to improve into
the weekend, and the winds back off in the second half of the
weekend. Until then, sure to stay fire weather aware!

-Murdock

&&

.SHORT TERM...
(This evening through Friday)
Issued at 202 PM PDT Thu Jun 19 2025

Satellite imagery reveals stratus clouds lingering across the
western San Mateo Peninsula and patches of the Monterey Peninsula.
These patches of cloud may be slow to mix out this afternoon, and
some inland stratus development is possible tonight through Friday
morning. A developing upper level low off the coast of British
Columbia is approaching the Pacific Northwest, with an associated
cold front cooling temperatures across the region by as much as 10
degrees compared to this time yesterday. Highs will reach the middle
70s to lower 80s in the inland valleys, the lower to middle 90s in
the southern reaches of Monterey and San Benito counties, the 60s
along the Bayshore, and the middle 50s to lower 60s along the
Pacific coast. Coastal drizzle is possible tonight into Friday
morning, with low temperatures generally in the middle 40s to the
middle 50s. Friday`s high temperatures will generally be similar to
today`s with further cooling in the inland valleys of the North Bay
and Central Coast, with high in the upper 60s to the middle 70s
across the inland valleys and the lower to middle 80s in the
southern reaches of Monterey and San Benito Counties.

The deepening upper level low to the north is causing a tightening
of the pressure gradient across the region, leading to strong and
gusty northwest winds developing through the day and lasting into
Friday. Gusts for this afternoon and evening will reach 25 to 40 mph
across the region, with the highest gusts along the coast, across
the ridgelines, through the gaps and passes, and within the Salinas
Valley. Particularly favored locations such as the Altamont Pass and
favored locations in the Salinas Valley may get gusts up to 50 mph
this afternoon and evening.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 202 PM PDT Thu Jun 19 2025

The strong gusts will continue into Saturday with the winds expected
to peak Friday evening. Through the weekend, the low pressure system
will begin to split, thus slackening the pressure gradient, with
some of its energy moving off into the Canadian prairie provinces,
leaving behind a more open trough across California. This open
trough will stick around for a few days with a strong upper level
ridge over the eastern United State blocking its path to the due
east. As a result, there will be a gradual warming trend into the
early part of next week, but nothing resembling a heat wave is
expected, with the high temperatures generally around seasonal
averages of the lower to middle 80s inland and the upper 60s to the
middle 70s along the Bayshore, while cooler conditions continue
along the Pacific coast with highs temperatures in the upper 50s to
middle 60s.

&&

.AVIATION...
(06Z TAFS)
Issued at 935 PM PDT Thu Jun 19 2025

Cold air advection, a deepening marine layer, upsloping winds and
radiative cooling favor coastal stratus /MVFR/ redevelopment with
local inland intrusions tonight and Friday morning. Drier air
arrives from the north and northwest Friday with clearing /VFR/
from north to south. Areas of strong and gusty west to northwest
winds continue through the evening, with some relaxation in winds
overnight then strengthening west to northwest winds redeveloping
Friday during the day. Based on recent HREF output, expect mainly
VFR except areas MVFR ceilings along the immediate coastline
Friday night and early Saturday morning.

Vicinity of SFO...Gusty onshore winds gradually easing overnight
then west wind strengthening again Friday with gusts to 35 knots.
BKN-OVC ceiling prevailing tonight to 15z-16z Friday. Radiative
cooling tonight will help restore a stratus feed to SFO for the
overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Onshore winds, cold air advection,
nocturnal cooling and a deepening marine layer support MVFR
stratus ceilings tonight and Friday morning. Stratus mixing
out to VFR by late Friday morning and SCT-BKN low clouds
return Friday evening and night. Onshore winds 10 to 15 knots
with occasional gusts to 20 knots.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 906 PM PDT Thu Jun 19 2025

Gale force winds will bring fresh swell, steep winds waves, and
hazardous conditions to the coastal waters through Friday. Onshore
flow will bring windy conditions to the bays as well. Winds will
be strongest across the outer waters and for the inner coastal
waters north of Point Reyes and south of Point Sur, where coastal
jets are expected to develop. Significant wave heights build to 10
to 12 feet across the coastal waters Thursday into the weekend
before abating early next week.

&&

.FIRE WEATHER...
Issued at 202 PM PDT Thu Jun 19 2025

Elevated fire weather conditions are setting up today across the
interior, with widespread RH values below 30% observed across the
interior of the East Bay south through the Gabilan Range, along with
the Santa Lucia mountains, combined with gusts of 20 to 25 mph.
Gusts are expected to increase to 25 to 40 mph across the interior
later this afternoon and evening, with strong gusts resuming Friday
and Saturday afternoon. Brief periods of critical fire weather
conditions are possible with daytime relative humidities of 15 to
25% in the interior. However, continuing marine layer influence,
especially during the night, and the fact that winds remain onshore,
mean that widespread critical fire conditions do not develop across
the district. Gusty winds begin to subside on Saturday, but the
upper level pattern will lead to more northerly winds developing
across the region. As with today`s fire weather threat, widespread
critical fire weather conditions are not expected within the
district, although the fire weather threat will increase for areas
closer to the Central Valley. The fire weather threat will continue
to diminish Sunday into the early part of next week with the gusty
winds further relaxing, although humidity values in the interior
will be slow to rise.

DialH

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for Mry Bay-SF Bay N
     of Bay Bridge.

     Small Craft Advisory from 1 PM to 9 PM PDT Friday for Mry Bay-SF
     Bay N of Bay Bridge.

     Gale Warning until 9 PM PDT Friday for Pigeon Pt to Pt Pinos 0-
     10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-
     60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to
     Pigeon Pt 0-10 nm.

     Gale Warning until 3 PM PDT Friday for Pigeon Pt to Pt Pinos 10-
     60 NM.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Canepa
MARINE...Canepa

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