921
FXUS66 KMTR 170032
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
532 PM PDT Mon Sep 16 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1203 PM PDT Mon Sep 16 2024

Rain showers will taper off from north to south through this evening
with temperatures remaining below seasonal averages through late
week. Another system enters the picture Wednesday with additional
rain chances, however rainfall amounts will be light. Warming into
the weekend.

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 1203 PM PDT Mon Sep 16 2024

Isolated rain showers continue over the region early this afternoon
and are expected to diminish in coverage while shifting southward
through this evening. Tonight, coastal drizzle will be possible as
moist conditions persist and troughing lingers over the region.
Temperatures overnight will be in the upper 40`s (in the coldest
interior spots) to mid 50`s for much of the region.

Tomorrow, temperatures will remain 5-15 degrees below average.
Outside coastal drizzle in the morning, tomorrow will be dry with
partial clearing of sky conditions through the afternoon.

&&

.LONG TERM...
(Tuesday through Sunday)
Issued at 154 AM PDT Mon Sep 16 2024

The next system set to come through Wednesday looks to be
very similar, but with slightly less of a wind threat. Still
looking at breezy winds in the same areas early Wednesday morning,
but more on the order of 25-35 mph as opposed to the 45-50 mph we
saw over the last 24 hours. A bit of a better chance for thunder
with the Wednesday system as well. Still a low chance (~15%), but
with a bit more cooling aloft and more lower level moisture, there
is more widespread instability late Tuesday night going into
Wednesday morning. Rain amounts still look to be on the lower
side, if any, similar to today. Beyond Wednesday there really
isn`t much noteworthy to write about. A casual warm up is on tap
going into the weekend that will bring our temperatures to around
seasonal normals. By the end of the weekend, there is some
discrepancy in ensemble guidance regarding the strength of a
possible ridge pattern. More on that in the coming days.

&&

.AVIATION...
(00Z TAFS)
Issued at 532 PM PDT Mon Sep 16 2024

It`s VFR-MVFR at the terminals with the greatest areal low cloud
coverage over the southern half of the forecast area this afternoon.
Where it is a mainly clear to clear start this evening and tonight,
radiative cooling will likely result in patches of valley fog
/VLIFR-IFR/ for late tonight and Tuesday morning. Otherwise where
cloud cover persists with VFR-MVFR, these conditions are likely to
prevail tonight.

The forecast gets more challenging Tuesday morning because the
18z NAM is forecasting a lower level cool front arriving along the
coast from the SF Peninsula to Monterey County coastline. The
front and cooler air intrusion are bounded below by the sea surface
and land and above by a thermal ridge (capping stability). The
HREF output shows a higher probability of IFR becoming focused in
this area along the coast Tuesday. Caveat, it may take a while for
ceilings and surface visibilities to improve Tuesday, lower level
cooling resulting in patchy light coastal drizzle.

Vicinity of SFO...VFR-MVFR, however the HREF is showing an
increasing probability of IFR 08z-18z Tuesday and the RAP model
shows IFR 09z through 16z Tuesday. Part of this may be due to
nocturnal radiative cooling including the arrival of the above
described lower level cool front Tuesday morning; may need to
amend the 00z TAF for IFR. Onshore wind near 15 knots decreasing
tonight to 5 to 10 knots then increasing to 15 to 20 knots Tuesday
afternoon and early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR-MVFR, similar to vicinity SFO the
HREF is showing an increasing probability of IFR beginning
(earlier) 06z Tuesday (this evening) through approx 15z Tuesday
when conditions may begin to improve over the southern Monterey
Bay Area due to increasing lower level cool air advection. Caveat,
downward low cloud ceiling development due to cool air advection,
gentle upsloping along the terrain and lowering visibilities in
either mist or drizzle may still take place during the mid morning
hours. It may take until late morning to early afternoon for
conditions to improve to MVFR-VFR. HREF indicates post 00z TAF
early return of low clouds along the Monterey Bay shoreline and
the Salinas Valley.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 442 PM PDT Mon Sep 16 2024

Northwest winds continue to gradually decrease today in the wake
of yesterday`s cold front. All gale warnings have expired as of 3
PM. Rough seas have built in the NW waters and will gradually
abate through the next 24 hours. There is a bit of a break on
Tuesday before a second cold front brings the return of strong NW
winds and rough seas to the exposed coastal waters. Overall it
will be a challenging week for smaller craft.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Tuesday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt
     to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....Behringer
AVIATION...Canepa
MARINE...DialH

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