Moss Beach California Weather Forecast Discussion

208
FXUS66 KMTR 101735
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1035 AM PDT Fri Oct 10 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 328 AM PDT Fri Oct 10 2025
- Isolated rain showers linger today in the North Bay
- Thunderstorm chances Monday into Tuesday
- Widespread rainfall Monday through Wednesday
&&
.UPDATE...
Issued at 903 AM PDT Fri Oct 10 2025
Radar returns are showing isolated showers in the northern outer
waters off Sonoma County, with most of the activity at present to
the north across and off the North Coast. The latest high
resolution models are pushing the time that the showers reach
Sonoma County to the afternoon hours. We will continue to monitor
the evolution of the shower activity over the rest of the day.
DialH
&&
.SHORT TERM...
Issued at 328 AM PDT Fri Oct 10 2025
(Today through Sunday)
A surface low pressure system in the Eastern Pacific Ocean will
continue to allow for isolated rain showers with the chance of an
embedded thunderstorm today - particularly in the North Bay and over
the waters. The upper-level low will weaken through the day today,
becoming an upper-level longwave trough tomorrow. The positively
tilted axis will swing through the region tomorrow, bringing
stronger onshore winds than the usual sea breeze circulation. The
region will remain under the influence of the upper-level longwave
trough through the weekend. Well below seasonal normal temperatures
and an increase in northwesterly winds will have the sensible
weather feeling cold, at least relatively speaking. This is
supported by the 00Z October 10th KOAK sounding which observed an
850 millibar temperature of 8.55 degrees Celsius which is near the
tenth percentile of 7.5 degrees Celsius for this date and time. If
you are looking for weekend plans, Sunday would be a great day to
clean out your gutters and properly secure outdoor items that could
be blown away so that your Halloween decorations don`t become your
neighbors!
&&
.LONG TERM...
Issued at 328 AM PDT Fri Oct 10 2025
(Monday through Thursday)
Global ensemble clusters are in agreement that a reinforcing upper-
level low will dig from the Washington/Canada border down off our
coast beginning Monday. The uncertainty with this system comes in
strength and location, and thus, timing. A stronger solution closer
to the coast will be wetter and result in more impacts than a weaker
solution farther inland which will be drier and result in less
impacts. As of now, it does look like everywhere will get over an
inch of rainfall between Monday and Wednesday with locally higher
totals of two to three inches in the higher terrain. As this is the
first widespread wetting rainfall (0.10 inch or greater) of the wet
season, there will likely be an increase in car accidents due to oil
separation on the roads. Please allow extra patience, space, and
time when driving. There is also a marginal risk (at least 5%
chance) of rainfall exceeding flash flood guidance meaning that
isolated flash floods will be possible, but localized and primarily
affecting places that can experience rapid runoff with heavy
rainfall. This system is also going to be cold. The 850 millibar
temperature that was discussed in the short term is forecast to drop
through Tuesday with the deterministic ECMWF and GFS forecasting it
to be somewhere in the 3-4 degrees Celsius range which would be near
the daily minimum. The cold air aloft will also allow for further
destabilization of the atmosphere, so with the critical thunderstorm
ingredients of lift, instability, and moisture all in place, there
is a slight chance for thunderstorms Monday into Tuesday before cold
air funnels in at the surface behind the cold front.
It is important to note that this system is not unprecedented, it is
not an atmospheric river, and it is not from typhoon remnants. These
distinctions are important so that decision fatigue and recency bias
are kept in check through our wet season so that when there is a
system that calls for stronger wording, it has not lost all meaning.
It`s all about context. Are we forecasting a month`s worth of rain
over the course of three days? Yes. It is important to keep in mind
though that October is the start of the wet season and water year;
thus, it is not too difficult to achieve the feat that we are
forecasting. For example: SFO`s average precipitation during the
month of October between 1945 and 2024 is 0.97 inches - their
rainfall total forecast between Monday and Wednesday is 1.36 inches.
Their maximum precipitation for the month of October is 7.30 inches
dating back to 1962 where 7.29 inches fell over the course of four
days during the Columbus Day Storm. All in all, this system should
generally be beneficial from a water storage and fire weather
standpoint.
&&
.AVIATION...
(18Z TAFS)
Issued at 1035 AM PDT Fri Oct 10 2025
Satellite imagery is showing stratus mixing out over the interior
valleys, mid-level cloud cover impinging into Sonoma County, some
cumulus developing from SJC down to the Monterey Bay region, and
generally VFR conditions everywhere else. VFR conditions are
generally expected to persist through the day, with some MVFR
ceilings possible as isolated showers move into the North Bay this
afternoon. Breezy onshore winds with a southeast component will
develop this afternoon across the region, extending into the
evening. Overnight, some MVFR-IFR ceilings are possible along the
coast, within the higher elevations, and within the North Bay
valleys. Some models are showing a band of showers moving across the
region overnight but outside of the North Bay confidence is low. Fog
is possible in the North Bay valleys tonight, but opted to keep it
out of the TAFs as confidence is low. Winds will start to increase
again on Saturday, towards the end of the 24-hour TAF period.
Vicinity of SFO... Moderate to high confidence of VFR through the
TAF period. Breezy west-southwest winds develop at the terminal this
afternoon into the evening with gusts up to 15 kt. Low confidence
(10-20% probability) of showers at the terminal this evening. Winds
diminish overnight, before turning to the northwest Saturday
afternoon with gusts to 25 kt.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... VFR through the day with breezy west-
northwest winds developing in the afternoon. IFR-MVFR ceilings
develop overnight over the nearby mountains, with moderate
confidence that they will impact the terminals. Any ceilings that
develop should clear out through Saturday morning with breezy and
gusty northwest winds developing in the afternoon beyond the TAF
period.
&&
.MARINE...
(Today through Wednesday)
Issued at 903 AM PDT Fri Oct 10 2025
Light showers with scattered thunderstorms are moving across the
northern outer waters this morning and will persist through much
of the day before shifting inland tonight. Light winds will
continue today and tonight, then begin to steadily increase across
our southern waters first on Saturday morning, and spread north
during the day. Increasing northwest winds across our area
Saturday will result in rough seas by Sunday. An unsettled pattern
for the first half of next week will bring more wind and rain to
the forecast.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Gale Watch from Saturday afternoon through late Saturday night
     for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt
     Piedras Blancas 0-10 nm.
Small Craft Advisory from 3 AM to 3 PM PDT Saturday for Pt Pinos
     to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH
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NWS MTR Office Area Forecast Discussion