FXUS66 KMTR 011120
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
420 AM PDT Tue Sep 1 2026
...New UPDATE, AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1039 PM PDT Mon Aug 31 2026
- Cooler weather continues through the week
- Beneficial wetting rain expected in the North Bay
&&
.UPDATE...
Issued at 416 AM PDT Tue Sep 1 2026
What was once Invest 95E off the coast of Mexico is now Tropical
Storm Marie, with the forecast track generally moving off to the
northwest. Ensemble model members are continuing to favor
solutions where the storm drifts off out to the open ocean away
from the state, and the confidence in any impacts to southern
California, let along the Bay Area and Central Coast, is
decreasing.
DialH
&&
.SHORT TERM...
Issued at 1039 PM PDT Mon Aug 31 2026
(Tonight through Wednesday)
Cool and wet. A deep 500 mb trough will slowly move towards the
coast over the next 24 hours. The marine layer is currently 3,200
ft deep as measured by the 00Z OAK sounding. This deep marine
layer, combined with the approaching trough, will very likely
bring some coastal drizzle Tuesday morning. Afternoon
temperatures will be 5-15 degrees below normal as the 850 mb
temperature drops below 10C/50F for the first time since May. By
Tuesday night a very weak cold front will bring a good chance for
light rain to the North Bay. This front will move southward
through the night and into Wednesday morning, bringing lower rain
chances to the rest of the Bay Area and Central Coast. Wednesday
will be similar to Tuesday with cool temperatures and another
chance for rain in the North Bay overnight as a second disturbance
moves through.
&&
.LONG TERM...
Issued at 1039 PM PDT Mon Aug 31 2026
(Wednesday night through next Monday)
Rain chances peak Thursday morning with an 90% chance of
precipitation in the North Bay, and a 70% chance of at least
1/10" at Santa Rosa. Again the rain chances fall off quickly as
the system moves south, but there's a decent chance (20-50%) for
lighter rain across the cwa. The cooler weather will continue
through Friday as the trough produces a cut-off low near the
Pacific Northwest. By the weekend, high pressure will build over
the desert SW. The interaction between the low pressure to the NW
and high pressure to the SE brings more uncertainty to the
forecast. If the trough is dominant the cooler weather will stick
around, if not then we can expect a warming trend this weekend.
The National Hurricane Center continues to track Invest 95E in the
Eastern Pacific. While there is now a 100% chance of tropical
cyclone formation over the next 48 hours, the circulation center
was displaced from the thunderstorm activity and it struggled to
get organized today. The eventual track of this system is still
uncertain, with the ensembles showing a bi-modal solution. One of
these outcomes would bring wind and rain to Southern California
around Sunday or Monday. Either the PNW cut-off low will move far
enough south to pull the decaying tropical cyclone towards
Southern California, or high pressure will build south of the low,
forcing the storm harmlessly to the NW. While there is a lot of
hype around different deterministic solutions, it's much more
appropriate to look at ensembles in this time range. Both the GEFS
and ECMWF ensemble show a 20-30% chance of tropical depression
level impacts in Southern California, and a 10-20% chance of
tropical storm type impacts. Even in the worst case scenario, our
cwa wouldn't get nearly as much rain or wind as Southern
California. The current high end scenario (90th percentile) would
bring 1/4" of rain to the Central Coast. The most likely outcome
is no significant impacts, and the ensembles have trended more in
that direction over the last 24 hours. There is virtually no
chance for hurricane impacts in California. It's worth watching if
another system forms behind 95E, as persistent troughing could
keep the door open through next week.
&&
.AVIATION...
(12Z TAFS)
Issued at 416 AM PDT Tue Sep 1 2026
Extensive MVFR to low-end VFR stratus should continue through the
sunrise hours, clearing back to the immediate coast through the
course of the post-sunrise hours into the early afternoon, with a
gentle to moderate onshore pattern wind developing in the afternoon
and evening hours. Tonight, lower confidence in stratus impacts as
the fringes of a decaying front begin to impact the region, with a
shift to a more southwest wind flow expected as the front or its
remnants approach. Greatest confidence in sub-VFR stratus
development will be in the North Bay, where light rain is possible
as the front passes late tonight into Wednesday morning.
Vicinity of SFO... MVFR stratus with gentle southwest winds through
the morning hours. A moderate westerly breeze develops in the
afternoon and evening hours, with winds turning to the southwest and
the south through the evening and overnight. Low confidence of MVFR
ceilings early Wednesday morning, with greater confidence in low-end
VFR clouds over the terminal, with a low confidence on the clearing
time on Wednesday morning.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... MVFR to low-end VFR ceilings persist
through the latter part of the morning. A gentle onshore wind perks
up through the afternoon and evening, with the winds turning from
the southwest over MRY this morning to the west for the afternoon
and evening. Low confidence in a return of stratus to SNS tonight,
and MRY early Wednesday morning, as winds diminish.
&&
.MARINE...
(Today through Sunday)
Issued at 416 AM PDT Tue Sep 1 2026
Gentle westerly to northwesterly breezes continue through the
week with intermittent periods of moderate breezes. Wind driven
seas remain slight to moderate through the week with a continuing
long period southerly swell driven by tropical cyclone activity.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Tue Sep 1 08:30:03 PDT 2026
From the National Weather Service
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