FXUS66 KMTR 150508
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1008 PM PDT Mon Sep 14 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1206 PM PDT Mon Sep 14 2026
- Cooling trend and below normal temperatures through mid-week;
return to seasonal temperatures late week into weekend
&&
.UPDATE...
Issued at 838 PM PDT Mon Sep 14 2026
Pleasant September day around the region under sunny skies and
closer to seasonal averages for temps. There was a warming of 3
to 8 degrees when comparing high temps from Sunday to Monday. 60s
and 70s near the coast with more widespread 80s across the
interior. The offshore gradient noted below eased and winds are
beginning to weaken too.
No update needed this evening, but will be watching the stratus
development closely. Patchy stratus is hugging the coast near
Monterey and Half Moon Bay. Forecast has more stratus developing
overnight as the offshore gradient relaxes further and flow
along with the coast over the waters.
&&
.SHORT TERM...
Issued at 1206 PM PDT Mon Sep 14 2026
(This evening through Tuesday night)
Today will be the warmest day of the upcoming week with a slight
cooling trend kicking off tomorrow. The upper level trough that
brought us cooler weather last week has progressed eastward towards
the Intermountain West. In its place, zonal flow has developed over
Central California with slight troughing to redevelop Tuesday. The
transition from more zonal flow to slight troughing will see
temperatures cool 2-5 degrees across the region. This will bring
interior temperatures down from the mid to upper 80s today to the
low to mid 80s tomorrow. Coastal areas stay cooler with highs in the
60s to 70s.
Moderate offshore winds were observed along the ridgeline of the
Vaca Range early this morning but have since been trending
downwards. Mt. St. Helena (elevation of 4340 ft) reported a NNE gust
of 40 mph at 2:40 AM which was the strongest wind gust observed from
this event. The SFO-WMC gradient peaked at -6.10 around 7AM this
morning and has since dropped to -4.90 as of 10AM. It is forecast to
shift positive (onshore) by late this afternoon with light onshore
winds returning everywhere. The return of onshore winds should help
marine stratus to redevelop/move inland tonight. The only caveat to
this is we currently have a dry airmass over us which could keep
stratus development limited for one more night. Breezy onshore winds
redevelop Tuesday afternoon and evening with gusts to around 20-30
mph most likely in the East Bay Valleys, Salinas Valley, higher
elevations, and directly along the coast.
&&
.LONG TERM...
Issued at 1206 PM PDT Mon Sep 14 2026
(Wednesday through next Sunday)
Troughing becomes more dominant by Wednesday as another upper level
low pushes into the Oregon/California border. We are not
anticipating any rain or thunderstorms for this system across our
region but it will bring an unusually cold airmass across our
region. High temperatures Wednesday and Thursday will be running 5-6
degrees below normal across the lower elevations and closer to 10-15
degrees below normal in the higher elevations and along the coast.
This will keep interior temperatures securely in the 70s and coastal
temperatures in the low to mid 60s. Favored hotspots across the
interior Bay Area and Central Coast will reach the low 80s. The
upper level low deepens and tries to become cut-off from the jet
stream Thursday into Friday. Fortunately, it is a quick moving
system and maintains a neutral tilt. If it took a more positive tilt
and dug in more over NE California/Nevada then it would be more
reminiscent of an inside slider which would raise offshore wind
concerns. As it stands right now, this system will just bring a
round of gusty onshore winds Wednesday into Thursday with gusts
peaking between 20 to 30 mph. Locally higher gusts are possible at
favored windy locations (Altamont Pass, higher elevations, etc.).
The passage of the upper level trough will allow the marine layer to
deepen and see a return of our nightly/early morning stratus along
the coast and portions of the interior.
Troughing influence wanes Friday into the weekend as weak ridging
builds in over California. This will see a gradual return to more
seasonal temperatures in the low to mid 80s across the interior, 60s
to 70s along the coast, and upper 80s to low 90s across favored hot
spots in the Bay Area and interior Central Coast. Even though the
ridge is weak, it will still compress the marine layer and most
likely result in less stratus cover across the interior.
&&
.AVIATION...
(06Z TAFS)
Issued at 1007 PM PDT Mon Sep 14 2026
Gentle to moderate onshore breezes continue this evening, becoming
light overnight. Above the surface, a weak offshore flow continues
to keep stratus out of most terminals this TAF period but will
gradually diminish by Tuesday morning. Wednesday night looks more
promising for widespread stratus due to the absence of an offshore
flow and the passage of an upper-level trough, which will allow the
marine layer to deepen. That being said, VFR prevails this evening
except at HAF where MVFR ceilings have already formed. Medium
confidence for APC to develop borderline MVFR-IFR ceilings early
Tuesday morning and scatter out by mid Tuesday morning. Diurnal
onshore breezes increase Tuesday afternoon into the evening.
Vicinity of SFO...VFR with gentle onshore breezes through the night.
Low confidence on the development of MVFR ceilings tonight,
therefore the TAF advertises SCT decks. If ceilings become robust
overnight, they will likely be short-lived and scatter out by late
Tuesday morning. Wednesday has a higher chance of developing MVFR
ceilings, likely after the current TAF cycle. Diurnal onshore
breezes prevail through the TAF period.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Gentle onshore winds continue through the
night and increase by Tuesday morning. High confidence for IFR
ceilings to develop around midnight, filling in over MRY first
followed by SNS. Stratus is expected to scatter out by late Tuesday
morning resulting in a short period of VFR conditions. An earlier
onset of MVFR stratus is expected tomorrow evening around sunset.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 1007 PM PDT Mon Sep 14 2026
Northwesterly breezes will begin to diminish tonight with
hazardous conditions for small craft lingering across the northern
waters at least into Wednesday morning. Moderate to rough seas
will prevail through Tuesday before subsiding to become slight to
moderate Wednesday through Friday.
&&
.FIRE WEATHER...
Issued at 436 AM PDT Mon Sep 14 2026
A few patches of coastal stratus have developed overnight. North
to northeast breezes have developed in the higher terrain. Offshore
winds will diminish by late morning or early afternoon and return
to diurnally breezy onshore winds in the afternoon and evening. A
surface to lower level trough of low pressure will develop along
the north Central Coast Tuesday through Tuesday night. Surface to
lower level troughing will expand to include the Bay Area Wednesday
through Thursday. This will bring higher humidity with good recoveries
from sea level to lower elevations to around 2500 feet, however above
this elevation especially along the higher ridgetops thermal ridging
and much lower humidity will persist during mid-week.
As such, areas above the marine layer often experience nocturnal
drying that will likely continue through early this upcoming week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt
Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory until 3 AM PDT Tuesday for Pt Pinos to Pt
Piedras Blancas 0-10 nm.
Small Craft Advisory until 9 AM PDT Tuesday for Pigeon Pt to Pt
Pinos 10-60 NM.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Navarrete
MARINE...Sarment
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Prepared by Boulder-Creek.com Weather at: Mon Sep 14 22:30:03 PDT 2026
From the National Weather Service
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