San Ramon, California Weather Forecast Discussion

023
FXUS66 KMTR 010018
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
518 PM PDT Tue Sep 30 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 233 PM PDT Tue Sep 30 2025
- Beneficial rain today into tomorrow
- Warming and drying trend kicks off Friday with the development
   of an inside slider
&&
.SHORT TERM...
Issued at 233 PM PDT Tue Sep 30 2025
(This evening through Thursday)
Isolated rain showers continue across the area - likely with the
help of a surface trough and orographic lift. A storm force low
pressure system off the Pacific Northwest Coast will spawn our
second cold front of the week. Moisture from what was Typhoon
Neoguri has been pulled into this system and as a result, the GEFS
and ECMWF IVT Forecast ensemble mean shows values remaining in
excess of 250 kg/ms for the next 24 hours. Pre-frontal rain showers
are beginning to enter the outer waters - expect these to enter
Sonoma County late this afternoon with increasing coverage and
intensity through the night as the cold front encroaches the Pacific
Coast. The cold front is slow moving and is expected to take near 24
hours to trek across our region, falling apart as it pushes
southeast. Rainfall with this system is expected to be beneficial.
&&
.LONG TERM...
Issued at 233 PM PDT Tue Sep 30 2025
(Friday through next Monday)
Global ensemble clusters continue to suggest that an inside slider-
like pattern will begin to develop by Friday as the upper-level
longwave trough that brought us active weather the past two days
pinches off a low. While there continues to be uncertainty in the
location and strength of the upper-level low (and thus, timing),
this aforementioned feature will develop over Northern California in
a way that will initially preserve onshore flow. By Saturday a
reinforcing upper-level shortwave trough will develop and dig
through Monday - this is when we can expect to see
northerly/offshore flow that will provide further drying. The
rainfall that we have accumulated over the past two days in addition
to what is expected the next two days will be beneficial, but not
fire season ending.
&&
.AVIATION...
(00Z TAFS)
Issued at 518 PM PDT Tue Sep 30 2025
Scattered showers continue to impact STS and APC with showers
gradually moving south tonight into tomorrow. Rain showers will
progress south of the North Bay by late tonight into early tomorrow
morning but will take longer to reach the Central Coast. Shower
chances will be highest for the Central Coast late tomorrow
afternoon/early in the evening. Ceilings will lower and become MVFR
tonight into tomorrow morning. It is likely that CIG heights will
bounce up and down as showers move across TAF sites and produce
temporary reductions in visibility and ceiling heights. Winds remain
moderate and southerly but are expected to shift more southwest to
westerly after cold frontal passage early tomorrow morning.
Vicinity of SFO...Breezy southerly winds continue through this
evening before winds ease overnight. Showers reach the airport by
early tomorrow morning and continue through tomorrow evening.
Moderate confidence that MVFR conditions will develop by late
morning and continue into the evening as cold frontal passage
occurs. Winds strengthen and shift to become more westerly by
tomorrow afternoon as the cold front passes the airport.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Gusty onshore winds continue before easing
late this evening. IFR-MVFR ceilings return tonight with showers
chances increasing early to late tomorrow morning. Highest
confidence in shower activity increasing late tomorrow afternoon
into the evening as the line slowly progresses southward. Winds
shift westerly to northwesterly after cold frontal passage tomorrow
afternoon.
&&
.MARINE...
(Tonight through next Monday)
Issued at 518 PM PDT Tue Sep 30 2025
A moderate to rough Northwest swell arrives to the outer waters
Wednesday with up to 12 foot wave heights. A cold front
associated with this storm will also move through Wednesday,
bringing a wind shift from S to NW. This system will bring gusty
conditions and some rain showers as it moves through. The swell
will gradually subside Thursday before a strong NW breeze develops
Friday. This will bring another round of rough seas and small
craft conditions to the coastal waters through Saturday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM Wednesday to 9 AM PDT Thursday
     for Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory from 3 PM Wednesday to 9 AM PDT Thursday
     for Pigeon Pt to Pt Pinos 10-60 NM.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Kennedy
MARINE...Murdock
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NWS MTR Office Area Forecast Discussion