609
FXUS66 KMTR 020421
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
921 PM PDT Tue Jul 1 2025

...New UPDATE, MARINE...

.KEY MESSAGES...
Updated at 229 PM PDT Tue Jul 1 2025

 - 10 percent chance for dry thunderstorms in the North Bay this
afternoon and evening.

 - Typical marine layer stratus pattern this week.

 - Near normal temperatures with a slightly below normal
   temperatures Thu & Fri.

 - Breezy northwest winds Thursday afternoon and evening.

&&

.UPDATE...
Issued at 920 PM PDT Tue Jul 1 2025

It has been a very active evening to our north with plenty of storms
popping off as the trough moves inland, but all of that convective
energy has failed to approach the Bay Area. The evening operations
team watched a thin and quick-moving boundary make its way down the
coast, plowing low clouds into San Francisco, and disrupting the
prevailing clouds at Half Moon Bay. But that was about it in the way
of excitement.

Very slight chances for convection linger in the North Bay into the
night, but these chances will erode into the morning.

Afterwards, the pattern settles back into the what we have been
seeing for almost the last week now, cloudy overnights, clearing
afternoons, and cloudy again into the evening.

&&

.SHORT TERM...
Issued at 229 PM PDT Tue Jul 1 2025
(This evening through Wednesday)

Satellite and radar analysis shows shower and thunderstorm activity
well to our north and east this afternoon. Looking at the SPC
mesoanalysis page, we appear to be well capped over the North Bay
which is helping keep convection suppressed. Though a batch of
cumulus clouds are streaming over the northern parts of Sonoma and
Napa counties. Webcams across this region show these as rather flat
and unimpressive looking. Should we be able to overcome the cap and
get enough forcing, either from the trough or the terrain, the
convective parameters appear to be healthy enough to support
fluffier clouds or some isolated thunderstorms.  PWATs, MUCAPE,
total-totals, steep-lapse rates, LIs, and DCAPE continue to be
picked up on. A few hi-res models support isolated thunderstorms
either developing or drifting into northern Sonoma or Napa counties
this evening; however, confidence is too low to add any mentionable
PoP or weather into the forecast for that.

Tomorrow, the upper low slips farther to the south and moves more
inland. Guidance  shifts convective activity more to the east, which
should put a kibosh on precip chances. This puts us back into our
stratus quo type of a forecast with nighttime and morning stratus,
which then clear for majority of the area except for those along the
coast.&&

.LONG TERM...
Issued at 229 PM PDT Tue Jul 1 2025
(Wednesday night through next Monday)

The forecast will be on semi-repeat for the long term, as weak upper
level ridging late Wednesday into Thursday, with an upper level
trough swinging through the PacNW and northern CA Thursday afternoon
and into Friday. This will bring cooler and breezier weather to the
region, and deepen the marine layer. More zonal like flow is
expected behind this quick moving trough, which will allow
temperatures to rebound a few degrees.

&&

.LONG TERM...
Issued at 229 PM PDT Tue Jul 1 2025
(Wednesday night through next Monday)

The forecast will be on semi-repeat for the long term, as weak upper
level ridging late Wednesday into Thursday, with an upper level
trough swinging through the PacNW and northern CA Thursday afternoon
and into Friday. This will bring cooler and breezier weather to the
region, and deepen the marine layer. More zonal like flow is
expected behind this quick moving trough, which will allow
temperatures to rebound a few degrees.

&&

.AVIATION...
(00Z TAFS)
Issued at 449 PM PDT Tue Jul 1 2025

VFR conditions prevail at the moment, but a robust stratus layer
offshore has begun to encroach inland. There is high confidence
that most terminals will develop IFR or LIFR ceilings this
evening, with a smaller chance for visibility reductions. These
conditions will persist through around 17-18Z Wednesday before
some brief clearing in the middle of the day.

Vicinity of SFO...A NW facing terminal camera is showing the fog
monster approaching over the peninsula. Despite the proximity,
most model guidance suggests these clouds will hold off for
several hours as the Bay fills in first and the ceilings
surround the terminal. The signs for this are already being
observed on satellite, with a line of clouds passing through the
Golden Gate towards the East Bay as the coastal clouds stay hung
up in the hills. Ceilings will eventually form overnight, and the
current cloud base looks to be near LIFR on the cameras, with HAF
currently reporting 300 feet.

SFO Bridge Approach...Ceilings should develop an hour or two
sooner over the approach than at the terminal.

Monterey Bay Terminals...Marine layer stratus has started to
return from the coast and will soon envelop both MRY and SNS with
LIFR ceilings that will last through the night. There is a
possibility for fog to develop at each site, but the TAFs are
conservative with mist for now. If the winds die, fog becomes more
likely.

&&

.MARINE...
(Tonight through next Monday)
Issued at 920 PM PDT Tue Jul 1 2025

A strong NW breeze and rough seas will continue through Thursday
before improving briefly improving late week. A low-amplitude long
period southerly swell will arrive Thursday and persist through
Friday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM to 9 PM PDT Wednesday for SF Bay
     N of Bay Bridge.

     Small Craft Advisory from 9 AM to 3 PM PDT Wednesday for Pt
     Arena to Pt Reyes 0-10 nm.

     Gale Warning from 3 PM Wednesday to 3 AM PDT Thursday for Pt
     Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM Wednesday to 9 AM PDT Thursday
     for Pigeon Pt to Pt Pinos 10-60 NM-Pt Reyes to Pigeon Pt 0-
     10 nm.

     Small Craft Advisory from 9 PM Wednesday to 9 AM PDT Thursday
     for Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Gale Warning until 3 AM PDT Thursday for Pt Arena to Pt Reyes 10-
     60 NM.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Flynn
MARINE...Flynn

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