Graton, California Weather Forecast Discussion

313
FXUS66 KMTR 021934
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1234 PM PDT Thu Oct 2 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 115 PM PDT Wed Oct 1 2025
- Showers moving south through the day with slight chance for
   thunderstorms in the interior Central Coast.
- Gusty winds developing on Friday
- Gradual warming trend begins this weekend with moderate
   offshore winds
&&
.SHORT TERM...
Issued at 1254 AM PDT Thu Oct 2 2025
(Today and tonight)
The 6Z WPC surface analysis depicts a stationary front parked
just off the coast of the Bay Area with a weak low pressure center
off of Monterey Bay. The offshore low pressure center has been
relatively still since it formed off the coast of Mendocino County
yesterday morning, but it will wade its way through the state
today, dragging the front with it. Thus, the band of scattered
showers that remains over the Bay Area should start to move
southward, leaving the Bay Area behind by the afternoon hours and
clearing the Central Coast through the late evening. Rainfall
totals are expected to be light, at most around a quarter of an
inch in the favored upslope regions of the Santa Cruz and eastern
Santa Clara Mountains.
A complicating factor will be the chance for thunderstorms in the
interior Central Coast as the front moves through this afternoon
and early evening. Thinking back to the three ingredients for
convection: moisture will come from a trailing system whose
moisture is being dragged into the state. Instability will come
from a developing upper level low moving into the state, with K
Index values of 30-35 degrees C suggesting the possibility for
scattered thunderstorms. Lift could come from the local topography
as is quite common in the area, but the cold front itself will
provide another source of lift, extending the thunderstorm risk
into areas of the Central Valley. The latest forecast update shows
the probability of thunder rising to around 15-20% across most of
San Benito County, with chances for thunderstorms around 10-15%
across Monterey County and the southern and eastern sections of
Santa Clara County.
Behind the front, expect a rather chilly day with high
temperatures ranging from the lower to middle 70s in the inland
valleys, and the upper 70s to lower 80s in southern Monterey
County, to the upper 60s to lower 70s along the bays, and the
lower to middle 60s near the Pacific coast. For context, these are
around 5 to 10 degrees below seasonal averages. Lingering showers
are possible through the night, especially in the interior
portions of the forecast area.
&&
.LONG TERM...
Issued at 1254 AM PDT Thu Oct 2 2025
(Friday through Wednesday)
The strong upper level low will move through the state through
Friday, with drier conditions across the region with the moisture
having moved off to our south. A strong pressure gradient over the
Bay Area and Central Coast will enhance northwesterly winds
across the region, with wind gusts reaching 25 to 35 mph at the
immediate coast, within the Salinas Valley, and through favored
gaps and passes across the region. Wind Advisories may prove
necessary if confidence in more widespread gusty winds increases.
Temperatures will be around the same as today for the Bay Area
with a drop expected in the Central Coast, with the southern
Monterey Bay region and northern Salinas Valley seeing highs in
the lower to middle 60s, while the warmest locations in southern
Monterey County reach highs in the lower to middle 70s.
The weekend features a warmup as the upper level low moves off
into the Great Basin. High temperatures range from the middle 70s
to the lower 80s in the inland valleys, the lower to middle 70s
close to the Bays, and the middle to upper 60s along the Pacific
coast. A surface high will develop in the northern Rockies,
setting up the possibility for moderate offshore flow Saturday
through Monday. These would usually raise fire weather concerns,
but the antecedent rainfall and the limited strength of the
offshore flow will mitigate the risk. The latest update of the
PGE-WRF model shows the SFO-WMC gradient reaching -2 to -6 mb,
which will cause some offshore flow, but keep it from being strong
enough to warrant any critical fire weather threats.
Beyond Monday, upper level troughing is expected to persist over
the western United States, at least through the middle part of
next week. CPC outlooks lean towards temperatures and
precipitation totals near the seasonal average into the middle
part of October.
&&
.AVIATION...
(18Z TAFS)
Issued at 1234 PM PDT Thu Oct 2 2025
Lower clouds are scattering with lingering light showers beginning to
exit the region. Expect mid-level clouds to prevail into the
afternoon but push east and south into the late afternoon and
evening. The afternoon brings moderate to breezy west winds that
last into the mid evening and early night before becoming light
again. Lower clouds build along the coast and the Monterey Bay, with
MVFR CIGs expected. These CIGs filter into the SF Bay later into the
night and STS gains IFR CIGs. Friday afternoon sees CIGS begin to
erode for all but the immediate coast.
Vicinity of SFO...Scattered low clouds with overcast mid-level
clouds continue into the mid afternoon but push east as breezy west
winds arrive. Winds become less breezy and reduce into the early
night with MVFR CIGs filling over the terminal into early Friday.
Expect these CIGs to exit into the late morning on Friday as
moderate winds build.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Light showers are dissipating and CIGs are
starting to rise. Expect more moderate winds along with low clouds
eroding into the mid afternoon, but mid-level clouds will linger.
Expect winds to reduce into the evening as MVFR CIGs fill over the
terminals. Light winds and CIGs last into the late morning and early
afternoon on Friday.
&&
.MARINE...
(Tonight through next Tuesday)
Issued at 1234 PM PDT Thu Oct 2 2025
Lingering shower activity stays in the souther waters through the
day and into the night.Winds increase into the late night and
through Friday, causing widespread hazardous conditions for small
craft. These winds will support rough wind waves up to 10 feet
through the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM Friday to 3 AM PDT Saturday for
     Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory from 9 PM this evening to 3 AM PDT Saturday
     for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60
     NM.
Small Craft Advisory from 3 AM Friday to 3 AM PDT Saturday for
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras
     Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.
Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
     to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...RK
LONG TERM....RK
AVIATION...Murdock
MARINE...Murdock
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NWS MTR Office Area Forecast Discussion