361
FXUS66 KMTR 192012
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
112 PM PDT Sat Sep 19 2026

...New SHORT TERM, LONG TERM, FIRE WEATHER...

.KEY MESSAGES...
Updated at 1229 PM PDT Sat Sep 19 2026

 - Warmer temperatures today

 - Brief cooling Sunday through Monday

 - More substantial warming trend Tuesday through Thursday

&&

.SHORT TERM...
Issued at 1229 PM PDT Sat Sep 19 2026
(This evening through Sunday night)

The marine layer is around 1,500 feet deep and the morning clouds
have pulled back to the coast. There is a weak offshore gradient
(SFO-WMC -3mb) that caused some moderate NE winds across the North
Bay and East Bay mountains early this morning. The sea breeze is
now taking over, flipping winds back onshore as the mesoscale
gradient weakens. A 500 mb short wave ridge axis will move over
the Bay Area this afternoon. This building ridge is causing
subsidence and warmer conditions in the lower atmosphere. Surface
temperatures are around 5 degrees warmer than this time yesterday
outside of the cloudy coast. That puts us right around normal for
this time of year.

A weak cut-off low will start to move in from the west Sunday. This
will reverse the warming trend and bring temperatures around 5-10
degrees below normal again. It will also encourage the the marine
layer to expand a bit.

&&

.LONG TERM...
Issued at 1229 PM PDT Sat Sep 19 2026
(Monday through next Friday)

The cut-off low will move overhead Monday. This will keep the cooler
temperatures in place, deepen the marine layer, and may bring
some morning drizzle to the coast and windward slopes. The ECMWF
shows some decent 850 mb vorticity, which will help create the
lift necessary to form drizzle drops within the deeper cloud
layer. These are still tiny drizzle drops though, so any
accumulation will be very light.

By Tuesday we will be on the backside of the low and a more
substantial warming trend will begin. A relatively low-amplitude
500 mb ridge will build through the middle of the week, but 850
temperatures will climb to 20 to 23C by Wednesday and Thursday.
That range is approximately the 75th to 95th percentile for this
time of year. Our current forecast has near normal temperatures
across the interior Tuesday, steadily building to 10 to 15 degrees
above normal by Thursday. With no sign of strong offshore winds,
a shallow marine layer will likely survive this warm-up, at least
through Wednesday. Heat Advisories are possible, but we`re getting
to the time of year where the nights are just as long as the
days, which really helps dull the accumulating impacts.

The ridge will start to break down Friday as a 500 mb trough
moves over the Pacific Northwest. This will bring temperatures
back down. There`s still no real chance for rain until the
following week.

&&

.AVIATION...
(18Z TAFS)
Issued at 1112 AM PDT Sat Sep 19 2026

Marine layer around 1000 feet with low cigs rapidly retreating
towards the coast. Expect all terminals to be VFR by 19z except
KMRY and KHAF. Low cloud deck to surge back inland tonight as next
shortwave trough approaches with slight deepening of the marine
layer overnight into Sunday.

Vicinity of SFO...Ceilings have cleared with west winds this
afternoon/evening. Low cigs to return after 05z tonight and
lasting at least through 18z Sunday.

SFO Bridge Approach...Approach is clear and will stay that way at
least through 06z tonight.

Monterey Bay Terminals...Low cigs to pull back to the coast by
19z. Low cigs may linger near KMRY for much of the day and then
spread back inland by 02z and down the Salinas Valley.

&&

.MARINE...
(Today through Thursday)
Issued at 418 AM PDT Sat Sep 19 2026

Moderate to fresh northwest winds persist through the weekend.
Strong gusts up to 30 kt are possible across the northern coastal
waters, the Big Sur coastal jet region, and Monterey Bay through
the day. Winds briefly diminish across the southern coastal
waters this morning, but increase again to fresh by the
afternoon. Slight to moderate wind driven seas prevail this
weekend and steadily build to rough early next week.

&&

.FIRE WEATHER...
Issued at 1229 PM PDT Sat Sep 19 2026

The marine layer is around 1,500 feet deep and compressing. There
were some offshore winds this morning, but the sea breeze is
taking over as the offshore gradient relaxes. Today will be warmer
and slightly drier than recent days, although winds will be
lighter through the peak burn period. Cooler and more humid
conditions arrive Sunday-Monday before a longer warming trend
Tuesday through Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Sunday for Pt Arena to Pt
     Reyes 0-10 nm.

     Small Craft Advisory until 3 AM PDT Sunday for Pigeon Pt to Pt
     Pinos 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Sunday for Pigeon Pt
     to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PDT Monday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PDT Monday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 3 AM PDT Monday for Pigeon Pt to Pt
     Pinos 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...RW
MARINE...RW

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