FXUS66 KMTR 011712
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1012 AM PDT Tue Sep 1 2026
...New AVIATION...
.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 915 AM PDT Tue Sep 1 2026
The deepening trough off of the Pacific Northwest and northern
California coasts is resulting in a mixing out of the marine layer
and temperatures as much as 20 degrees cooler than seasonal
averages. As such, ceilings have been around 3000 ft or greater much
of the night and into early this morning. Expecting these low clouds
to mix out and bring mostly sunny skies this afternoon. The
exception will be over the North Bay where high level clouds will
persist through much of the day. So updates are anticipated at this
time as the ongoing forecast remains on track.
RGass
&&
.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...
(18Z TAFS)
Issued at 1006 AM PDT Tue Sep 1 2026
VFR conditions are expected to prevail through the forecast period
for all terminals. A deepening trough will continue to mix out
lingering low level clouds by early afternoon.
Vicinity of SFO...VFR with occasionally breezy onshore flow this
afternoon and early evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR is expected to prevail through the
forecast period with a slight chance of MVFR ceilings developing
after midnight.
&&
.MARINE...
(Today through Sunday)
Issued at 915 AM PDT Tue Sep 1 2026
Light northwesterly breezes will persist through the week with
occasional moderate breezes. Slight to moderate wind driven seas
will continue through the week with tropical cyclone activity
producing long period southerly swell by the end of the week into
the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...JM
MARINE...JM
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea
Prepared by Boulder-Creek.com Weather at: Tue Sep 1 12:30:03 PDT 2026
From the National Weather Service
|