Knightsen, California Weather Forecast Discussion

402
FXUS66 KMTR 290450
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
950 PM PDT Sun Sep 28 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 235 PM PDT Sun Sep 28 2025
- Rain and a chance for thunderstorms returns tomorrow
- Rain lingers through Wednesday
- Warming and drying trend kicks off Friday
&&
.UPDATE...
Issued at 821 PM PDT Sun Sep 28 2025
Forecast for an unsettled pattern to bring increasing rain chances
the next few days remains on track. The forecast trend has been
drier the past couple of days leading up to the first cold front
arriving on the shores of the North Bay around sunrise Monday
morning. There is a slight chance for non-severe thunderstorms
Monday afternoon across the North Bay, otherwise expect periods of
scattered light rain most of the day and evening over the North
Bay and farther south into the Bay Area and Central Coast Monday
afternoon and evening. After a lull in widespread rain chances
Tuesday afternoon and Tuesday night will precede the second front
that will move slowly over much of our area on Wednesday with
another increase in rain chances for most of our area. We start
to dry out by Thursday afternoon with gradual warming into next
weekend.
&&
.SHORT TERM...
Issued at 235 PM PDT Sun Sep 28 2025
(Today)
The marine layer is currently being observed at 3,600 feet on the
Fort Ord Profiler with cloud ceilings lifting and drizzle being
observed in coastal and upslope areas. Temperatures are cooler
nearly everywhere away from the coast as compared to 24 hours ago.
High clouds from an approaching low pressure system off the Pacific
Northwest Coast are beginning to filter into the region - expect
these to lower through the day as the system nears. The smoke that
filtered into the region overnight is being sent back north thanks
to southerly winds ahead of the aforementioned system.
&&
.LONG TERM...
Issued at 235 PM PDT Sun Sep 28 2025
(Monday through next Saturday)
A low pressure system off the Pacific Northwest Coast and its
accompanying cold front will trek into the region tomorrow. The
moisture source is from the subtropics with the GEFS and ECMWF
Ensemble IVT Forecast ensemble mean near 350 kg/ms. Tomorrow morning
the region will be within the warm sector; thus, sensible weather
will be light rain with increasing southerly winds. As the cold
front pushes inland tomorrow afternoon, rainfall rates will increase
as the rainfall becomes relatively intense. Tomorrow will hold the
best thunderstorm chances for the week as the essential ingredients
of lift, instability, and moisture are there. With plenty of lift
and moisture, instability seems to be the limiting factor with low
CAPE and lapse rates on the cusp of stable/conditionally unstable.
The best environment will be over the Pacific Ocean with ingredients
becoming less favorable on land. This system has a moisture
trajectory from the southwest - this means two things. Firstly,
southwest facing terrain will likely be the rainfall total winners
with northwest-southeast oriented valleys getting rainshadowed.
Secondly, as the upper-level shortwave trough and surface cold front
are coming from the northwest with a southwest to northeast
direction, it means that it will be parallel to the moisture. This
will likely result in slow motion of the cold front with it
potentially becoming stationary which would provide an area for
continued rainfall. Fortunately, rainfall totals have lowered as the
system has trended farther north. We will still watch for any
potential of training rain showers/thunderstorms which would pose
the risk of flooding. System two on Wednesday will be very similar
sensible weather wise to system one with warm sector light rain and
increasing southerly winds followed by relatively intense rainfall
as the cold front moves through. Some differences are: the moisture
source is from Typhoon Neoguri in the Northwestern Pacific Ocean,
there`s even less favorable thunderstorm ingredients, and the upper-
level longwave trough becomes more progressive - thus, it is less
likely to linger. When all is said and done the North Bay can expect
to get up to 1.00" while the Interior Central Coast may get nothing.
Warming and drying trend kicks off Friday as high pressure builds in
from the Eastern Pacific Ocean.
&&
.AVIATION...
(06Z TAFS)
Issued at 950 PM PDT Sun Sep 28 2025
Extensive mid-level to MVFR cloud cover blankets the Bay Area and
much of the Central Coast and is expected to persist through the
night. An approaching front on Monday will cause ceilings to lift
and southerly winds to increase, with scattered pre-frontal showers
possible at the immediate coast. The main rain band begins to impact
the North Bay towards Monday afternoon and evening, but starts to
break up as it heads southward towards the end of the TAF period.
The coastal regions and the East Bay Hills look to give the best
chances for precipitation late Monday through Tuesday.
Vicinity of SFO... Overcast conditions persist through the night
with MVFR to mid-level ceilings. Breezy southwest winds resume
Monday afternoon with an approaching cold front. Low confidence for
scattered pre-frontal showers at SFO tomorrow afternoon, with
greater confidence in the western side of the San Mateo Peninsula
and at OAK. The main rain band approaches the terminal Monday night
and Tuesday morning, but is expected to break up as it moves down
from the North Bay, limiting confidence in precipitation at the
terminal.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... Widespread MVFR to mid-level clouds return
this evening and persist through the day Monday as a cold front
approaches. Light winds overnight before the onshore winds turn
towards a more southerly direction on Monday afternoon. Pre-frontal
showers could impact the coast through the day Monday but beyond the
TAF period, the main rain band is not expected to survive long
enough to bring rain to the region.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 950 PM PDT Sun Sep 28 2025
Gentle to moderate southerly winds generally prevail across the
majority of the coastal waters through late this week. An upper
level trough and surface cold front brings rain showers to the
coastal waters Monday into early Tuesday with embedded
thunderstorms possible across the northern waters. A second system
will bring additional rain showers to the waters late Tuesday
into Wednesday. Each system may bring isolated to scattered fresh
to strong wind gusts for the northern waters. Seas become moderate
to rough and build to 10 to 12 feet mid to late week with winds
expected to strengthen again late week into next weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH
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NWS MTR Office Area Forecast Discussion