FXUS66 KMTR 171953
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1253 PM PDT Thu Sep 17 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1211 AM PDT Thu Sep 17 2026
- Cooler temperatures continue today
- Warming trend Friday into the weekend
&&
.SHORT TERM...
Issued at 1241 PM PDT Thu Sep 17 2026
(This evening through Friday night)
A cut-off low overhead allowed the marine layer to expand to
nearly 5,000 feet this morning. This brought stratus to the vast
majority of the Bay Area, where it still remains early this
afternoon. The deep marine layer is also keeping temperatures
around 10 degrees cooler than normal for this time of year.
The cut-off low will gradually weaken and move off the
the NE over the next 24 hours. This will allow a short wave ridge
to slide in from the west, increasing temperatures and compressing
the marine layer Friday through Saturday.
&&
.LONG TERM...
Issued at 1241 PM PDT Thu Sep 17 2026
(Saturday through next Wednesday)
Saturday looks like the warmest day of the weekend as the 500 mb
short wave ridge axis moves over the Bay Area. There is also a
hint of weak offshore winds, but the SFO-WMC gradient isn't
expected to drop much below -2 mb. Another, much weaker, cut-off
low will move over Sunday, dropping the temperatures a bit.
Basically Saturday will be a couple degrees warmer than normal
and Sunday will be a couple degrees cooler than normal.
It now looks like a steady warming trend arrives next week. The
850 mb temperature (measured at about 5,000 ft) is expected to
hover around 20C (68F). That's around the 75th percentile for this
time of year. Not enough for a major heat wave, but enough to
bring surface temperatures 5-10 degrees above normal through the
middle of next week.
&&
.AVIATION...
(18Z TAFS)
Issued at 1046 AM PDT Thu Sep 17 2026
Low clouds will gradually scatter out into the early afternoon
hours, giving way to VFR conditions across area terminals. Light
winds will increase this afternoon with a moderate onshore breeze
developing. The marine layer is anticipated to return this
evening. Latest models indicate the marine layer will compress
overnight resulting in lower cigs overnight into Friday.
Confidence is moderate with respect to timing and cig heights.
Vicinity of SFO... VFR cigs will gradually scatter out by the
afternoon, with a moderate onshore breeze developing in the
afternoon. Cigs will return this evening and persist through the
overnight hours, with moderate confidence in timing and ceilings
height.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... VFR cigs will scatter out by early
afternoon with a gentle west-northwest wind developing. Winds
will ease overnight becoming light and locally variable with low
clouds anticipated to return. Confidence in timing is moderate.
&&
.MARINE...
(Today through Tuesday)
Issued at 911 AM PDT Thu Sep 17 2026
Gentle to light breezes persist through Friday morning with mild
seas across the coastal waters. A shift occurs Friday afternoon as
northwesterly winds ramp up to fresh to strong breezes. Small
Craft Advisories take effect Friday afternoon for Monterey Bay and
the southern coastal waters from Pigeon Point south down to Point
Piedras Blancas. Winds remain enhanced through the weekend,
maintaining hazardous conditions for small craft while overall
seas remain light to moderate through Sunday.
&&
.FIRE WEATHER...
Issued at 421 AM PDT Thu Sep 17 2026
The coolest conditions and deepest marine layer are expected through
the day today as the upper level low stalls over northern
California. Current observations suggest a marine layer depth of
over 3000 feet, allowing for moist conditions to reach very high
into the higher elevations. As the low moves away on Friday, the
marine layer will compress, temperatures will rise, and relative
humidities in the higher elevations will start to decrease. Some
offshore flow is possible on Saturday morning, but it is not
expected to be very strong and the bulk of the offshore influence
will be felt on the higher terrain of the North and East Bay.
DialH
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM Friday to 3 AM PDT Saturday for
Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory from 3 PM to 9 PM PDT Friday for Pt Pinos
to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...CW
MARINE...Heinlein
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Prepared by Boulder-Creek.com Weather at: Thu Sep 17 16:30:02 PDT 2026
From the National Weather Service
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