Larkspur, California Weather Forecast Discussion

827
FXUS66 KMTR 060915
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
215 AM PDT Sat Sep 6 2025
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1250 AM PDT Sat Sep 6 2025
- Cooler weather continues into next week.
- Chance for light rain early next week across the North Bay.
&&
.SHORT TERM...
Issued at 1250 AM PDT Sat Sep 6 2025
(Today and tonight)
Conditions at the surface are fairly similar to 24 hours ago,
however the satellite picture shows a much more patchy stratus
layer over the ocean. This indicates some dry air intrusion, which
will likely limit drizzle this morning. As a result we`ve decided
to remove drizzle from the forecast this morning, but some coastal
areas could still see a few small drops through the early morning
hours. Otherwise the skies will mostly clear in the late morning
with gentle to moderate onshore winds. Temperatures will remain
cooler than normal, similar to yesterday.
&&
.LONG TERM...
Issued at 1250 AM PDT Sat Sep 6 2025
(Sunday through Friday)
The 500 mb trough offshore will gradually deepen and approach the
coast through the weekend. This system is supported in the upper
levels by a dip in the PFJ brought on by a low pressure system
dropping down from the Gulf of Alaska. At the surface, a cold
front will push through on Monday, accompanied by a moisture plume
with PW around 1.0". This front has a decent chance to bring
light pre-frontal rain to the North Bay with lower chances further
south. After the front passes, cold air aloft will decrease the
stability and bring a slight chance for showers and thunderstorms
front Monday night through Wednesday. The ECMWF lightning flash
density product suggests the best chance is across the North and
East Bay on Wednesday afternoon. The ECMWF point sounding for
Santa Rosa shows surface based CAPE jumps to 580 J/kg, which is
very skinny and highly dependent on surface temperature. An LREF
analysis shows the mean CAPE closer to 150 J/kg, suggesting ECMWF
is on the high end of the guidance envelope. We`ll have to wait
for more high resolution CAMs to resolve this instability, but
either way this pattern will continue to bring cool humid
conditions with periods of gusty winds. 850 temps and 500 mb
height will gradually rebound late week, likely bringing
temperatures back to normal by the following weekend, but there is
an alternate scenario where a reinforcing trough moves in and
brings another round of disturbed weather.
&&
.AVIATION...
(06Z TAFS)
Issued at 928 PM PDT Fri Sep 5 2025
Currently a mixed bag of IFR-VFR at the terminals. The marine layer
is currently being observed at 2,500 feet with patchy and rather
unhealthy looking stratus across the region. The reason for this is
a surface low pressure system that is encroaching the Northern
California Coast is advecting some dry air. As such, confidence
has lowered since last TAF issuance to moderate that all terminals
will develop sub-VFR ceilings - likely on the cusp of IFR/MVFR and
later than originally forecast.
Vicinity of SFO...Currently VFR with westerly flow. Moderate
confidence on an MVFR ceiling redeveloping tonight. Westerly winds
will prevail through the TAF period.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Currently IFR with westerly flow at MRY and
MVFR with westerly flow at SNS. Moderate confidence on SNS further
deteriorating to IFR. VFR will prevail by tomorrow afternoon with
low stratus sticking close to the coast.
&&
.MARINE...
(Tonight through next Thursday)
Issued at 928 PM PDT Fri Sep 5 2025
Gentle to moderate northwesterly breezes and moderate seas will
prevail through Tuesday. Locally strong gusts can be expected with
the afternoon sea breeze.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Sarment
MARINE...Sarment
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NWS MTR Office Area Forecast Discussion