FXUS66 KMTR 141909
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1209 PM PDT Mon Sep 14 2026
...New SHORT TERM, LONG TERM...
.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
&&
.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...
(18Z TAFS)
Issued at 1004 AM PDT Mon Sep 14 2026
VFR at all terminals this morning with onshore winds forecast to
increase through the afternoon before easing after sunset.
However, the forecast wind speeds will be less than previous days.
Moderate confidence for the return of stratus over the Bay Area
terminals tonight with higher confidence for the Monterey Bay
terminals. Onshore winds increase once again by Tuesday afternoon.
Vicinity of SFO...VFR. Onshore winds are forecast to increase
throughout the afternoon with gusts up to 25 kt before gradually
easing late in the night. Moderate confidence for stratus at
around 1500 feet to arrive around 10Z Tuesday before scattering
out by 17Z. However, the HRRR does not suggest ceilings make it
over SFO. Thus, leaning more on the NBM and GFS-LAMP guidance.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR. Onshore winds increase this
afternoon and gradually diminish after sunset. Moderate to high
confidence for IFR/MVFR ceilings to return late this evening and
into Tuesday
&&
.MARINE...
(Today through Saturday)
Issued at 1004 AM PDT Mon Sep 14 2026
Hazardous conditions for small craft will continue for the coastal
waters and Monterey Bay early in the week due to a northwesterly
moderate to fresh breeze with strong gusts. Northwest winds will
ease by mid-week. Moderate to rough seas will prevail through
Tuesday before subsiding Wednesday.
&&
.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 9 PM PDT this evening for Mry Bay-
Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 3 AM PDT Tuesday for Pt Arena to Pt
Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt
Reyes 10-60 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...RGass
MARINE...RGass
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Prepared by Boulder-Creek.com Weather at: Mon Sep 14 12:30:03 PDT 2026
From the National Weather Service
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