320
FXUS66 KMTR 092005
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
105 PM PDT Fri May 9 2025

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 1207 PM PDT Fri May 9 2025

Clear skies and warm temperatures will continue through Saturday
before a cold front brings much cooler temperatures, strong winds
and a chance for rain starting Sunday.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 1207 PM PDT Fri May 9 2025

Temperatures are running about 10 degrees warmer than this time
yesterday as a substantial 500 mb ridge of high pressure builds
over southern California. This ridge is compressing the marine
layer to about 500 feet, which is keeping the skies clear for most
of the region, though some on the immediate coast could see the
marine layer fog monster ruin their picnic in the early afternoon.
Otherwise temperatures are on track to reach the forecasted highs
(generally upper 80s for the inland valleys and upper 60s to low
70s along the coast). Winds are generally light to moderate and
onshore. Saturday will essentially be a repeat of Friday with
temperatures remaining well above normal, although there will
likely be some high clouds and increasing winds in the evening.
These changes are signaling a major shift in the weather pattern
going into Sunday.

&&

.LONG TERM...
(Saturday night through next Thursday)
Issued at 1207 PM PDT Fri May 9 2025

A deep trough will approach the west coast by Sunday. This system
will bring several days of disturbed weather, highlighted by much
cooler temperatures and strong onshore winds. The temperature
swing from Saturday to Sunday is notable for the Bay Area. For
example, the high forecast for Santa Rosa drops from 85 to 68
across the 2 weekend days. I checked to see when the last time
we`ve had a big drop like that, and it turns out it wasn`t that
long ago. From March 25-26 the high actually dropped further from
85 to 57. The trough will continue to dig south through Tuesday
morning, further decreasing temperatures. This system will also
bring strong onshore wind. The 500 mb winds should peak around 90
kts Monday afternoon, and will spend most of the day above 50 kts.
With cold air aloft decreasing the vertical stability, 40-50% of
this wind speed can mix down to the surface, equating to
occasional wind gusts reaching as high as 50 mph. Our official
forecast is more conservative with gusts in the 20-30 mph range.
The windiest times will be when the atmosphere is well mixed
Sunday and Monday afternoon/evening, especially in higher
elevations. We are also expecting some rain from this system,
mainly confined to Monday as the front moves through. Most of the
cwa has a chance of some rain, with up to 1/4" expected in the
North Bay. The NBM continues to lag behind other guidance in both
POP and QPF, and I`ve adjusted the forecast to find a good middle
ground in these variables. Finally, the cold air mass aloft and
lingering low-level moisture will create some instability late
Monday-Tuesday in the post frontal environment. The upper level
trough will still be over the west coast and could easily spin off
short wave triggers for strong convection. There is a slight
chance for thunderstorms both Monday and Tuesday, but all we can
say for now is that the ingredients are there. We don`t know if
they will all line up at the right time yet. Otherwise the weather
will begin to stabilize mid week as a ridge starts to rebuild,
inland temperatures recover back to seasonal norms, and the
typical marine layer pattern returns.

&&

.AVIATION...
(18Z TAFS)
Issued at 1034 AM PDT Fri May 9 2025

VFR conditions expected through the TAF period. The exception will
be KHAF with low ceilings and reduced visibilities likely to return
early Saturday morning. Otherwise, high clouds are forecast to build
in this afternoon and become more widespread through tomorrow,
especially across the Bay Area terminals.

Vicinity of SFO...High confidence for VFR conditions through the TAF
period. West to northwest winds increase this afternoon with gusts
up to 25kt. By late evening, winds diminish slightly but will remain
out of a west to northwest direction. Around 16Z Saturday, winds
will potentially become offshore for a brief period before turning
onshore by around 22Z.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Moderate to high confidence for VFR
conditions through the TAF period. Onshore winds increase this
afternoon and diminish by this evening. Light winds are expected
overnight and early Saturday morning.

&&

.MARINE...
(Today through Wednesday)
Issued at 1034 AM PDT Fri May 9 2025

A fresh to strong northwesterly breeze will persist across much of
the coastal waters through the weekend, with up to near gale force
gusts. Light rain will be possible on Monday as a frontal passage
moves across the region. Moderate seas continue through the end of
the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT Saturday for CAZ516.

PZ...Small Craft Advisory until 3 AM PDT Sunday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt
     Reyes 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 9 AM Saturday to 3 AM PDT Sunday for
     Pt Reyes to Pigeon Pt 0-10 nm.

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

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

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...RGass
MARINE...RGass

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