670
FXUS66 KMTR 150552
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
952 PM PST Thu Nov 14 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1252 PM PST Thu Nov 14 2024

Isolated showers and thunderstorms move through the region today,
with chilly temperatures continuing into the early part of next
week. Warming trend begins in the middle of the week.

&&

.UPDATE...
Issued at 842 PM PST Thu Nov 14 2024

Key changes for the evening update:
-Shower/isolated storm potential persist across the Central Coast
-Snow flurries and/or light snow across higher terrain of the
 interior Central Coast (no significant accumulation anticipated)
-Conditional dense fog potential across the North and East Bay

Overall, the short term forecast is in good shape, with only some
changes to PoPs this evening to account for ongoing trends.

A large upper trough continues to ease eastward across the Bay
Area and Central Coast this afternoon. The loss of daytime heating
has resulted in a dramatic reduction of some of the deeper
convective elements---mostly showers. However, with the main upper
trough still to the west of the area, we`ll continue to be in a
regime that favors large scale ascent. As a result, precipitation
chances don`t completely go away and in fact, they ramp up,
largely across the Central Coast late tonight into Friday
morning. Short-term forecast soundings near Monterey, actually
reveal around 200-300 J/kg of CAPE will be in place as the
strongest forcing for ascent arrives (and we`re seeing a
manifestation of that on KMUX currently). What`s more noteworthy
is that the depth of the instability extends a little deeper in
the atmosphere. This could favor the generation of more favorable
hydrometeors to support charging and thus lightning. The conveyor
of greatest instability is expected to stretch from the offshore
waters southeastward toward Monterey Bay and even into western
portions of the Central Coast Interior. As such the forecast
continues to mention a 15 to 20 percent chance for isolated
storms, in addition to a 30-70 percent chance for rain showers
during late tonight into Friday morning. Bottom line is, I
wouldn`t be surprised if folks hear a rumble of thunder or two
tonight across the Central Coast.

As the cooler air aloft associated with the upper low spills
across the area, snow levels will fall down to around 3800 ft AGL.
This in tandem with the convective nature to the precipitation
may produce brief burst of snow flurries and/or light snow, across
the higher terrain of the Santa Lucia Range. In fact, probabilities
of a dusting on some of the peaks (e.g., Chews Ridge) is around
50% per blended guidance.

The last noteworthy item is fog across the North and East Bay.
While confidence is medium that model guidance has a good handle
on the low level wind field (which will be the limiting factor),
recent rainfall averaging between 1/4 to 1/2 an inch across the
North and East Bay means we`ll have to be mindful that if winds
diminish, the potential for radiational fog will increase quickly.
For now, I`ll advertise some patchy to areas of fog across
interior Napa County prior to sunrise Friday, but trends will be
monitored.

&&

.SHORT TERM...
(This evening through Friday)
Issued at 1252 PM PST Thu Nov 14 2024

Radar imagery shows scattered showers moving through the North Bay,
and heading south into the San Francisco and Oakland areas. These
showers should continue through the day with the possibility for
isolated thunderstorms setting up through the afternoon. Quick recap
of convective meteorology: the three ingredients for a thunderstorm
are instability, moisture, and lift. Instability will come courtesy
of the interaction of a strong upper level trough cooling the mid to
upper levels, with daytime solar heating warming the lower layers,
resulting in an increase in CAPE across the region. The latest high
resolution model runs show up to 600-700 J/kg of CAPE across the Bay
Area, a pretty significant value for our part of the world. As for
lift, the two potential sources for lift are a weak cold front that
will approach the region through the day, and surface-level winds
being forced to rise over our numerous mountain ranges (in the
business we call this "orographic forcing"). The limiting factor
will be moisture. The 12Z sounding over Oakland measured a
relatively mid 0.66 inches of precipitable water (PWAT). For
context, the seasonal average PWAT value is 0.59 inches, and a PWAT
value of 0.93 inches would lie above 90% of all OAK soundings
reported at this time of year. Thus, any convection that does form
will be isolated and rainfall totals will be quite light. The SPC
continues to show a risk of non-severe thunderstorms for the Bay
Area through the day today, and although the showers will move into
the Central Coast this evening, the lack of solar heating should
drastically limit the threat of convective activity.

Highs today range from the upper 50s to the mid 60s in the lower
elevations, down to around 50 in the higher elevations. On Friday,
the weak cold front should cause morning temperatures to dip to the
mid 30s to lower 40s inland and the mid to upper 40s along the
coast, while afternoon highs reach 50s and lower 60s in the lower
elevations, and the lower to mid 40s in the higher elevations.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 1252 PM PST Thu Nov 14 2024

Even colder low temperatures are expected to develop Friday night
into Saturday morning. Temperatures near or at the freezing level
are forecast along the Salinas Valley south of Greenfield, the
higher elevations of the Central Coast, and the Sonoma County
valleys; lows will fall down into the upper 30s across the inland
valleys while the coast and Bayshore see lows in the low to mid 40s.
A Freeze Warning, issued partially due to high confidence in
freezing temperatures and partially due to partner support, will go
into effect from midnight Friday night through 8 AM Saturday morning
in the interior North Bay, southern Salinas Valley, and the interior
mountains of Monterey and San Benito Counties, with a Frost Advisory
in effect for the same time period for the northern Salinas Valley
and the Santa Lucia ranges.

Another trough arrives Sunday into Monday, maintaining temperatures
from near the seasonal average to 10 degrees below seasonal
averages, and although most of the rainfall with this system is
aimed at the Pacific Northwest, a few meager showers could make
their way to the Bay Area. Once the trough clears out, ridging
should build into the western United States and contribute to a
warming trend that sees the inland valleys return to highs in the
low to mid 70s, around 5 to 10 degrees above seasonal averages. The
end of the next week sees the potential for a troughing pattern to
return to the region, and CPC products suggest a lean to
temperatures and precipitation totals above seasonal averages
heading into Thanksgiving.

&&

.AVIATION...
(06Z TAFS)
Issued at 951 PM PST Thu Nov 14 2024

Mostly VFR ceilings but some coastal terminals are experiencing
occasional MVFR/IFR/LIFR conditions. Therefore, TEMPO groups were
included for possible low ceilings for KHAF and KSNS. The
possibility of light vicinity showers will continue overnight into
Friday morning. There is a chance for some low ceilings to develop
in the North Bay if winds become very light, but confidence is low
to include in TAFs at this moment. Winds are predominately light to
moderate but the post-frontal environment will help winds build to
moderate to breezy winds overnight. By Friday afternoon, winds will
become gusty with speeds up to 26 knots.

Vicinity of SFO...VFR through the TAF period. Light vicinity showers
is still possible overnight, but conditions will remain VFR. Onshore
winds have become breezy and gusty. There is some uncertainty on how
long the gust will last, but overall winds will be pretty
breezy/strong through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Predominately VFR but MVFR ceilings have
lingered near KSNS. There is some uncertainty on when stratus will
lift, but expect near 08-09Z. By morning VFR should prevail through
the TAF period for both terminals. WInds will become gusty and
breezy by Friday afternoon.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 951 PM PST Thu Nov 14 2024

Isolated light showers continue to move through the waters tonight
into the morning with a slight thunderstorm potential. Expect
rough to very rough seas to continue through Saturday as moderate
to large northwest swell builds. Significant wave height of 13-16
feet will continue through the weekend creating hazardous
conditions over the waters. Northwesterly breezes increase to
become strong by Friday with gale force gusts possible. Winds
diminish and seas abate into next week.

&&

.BEACHES...
Issued at 1252 PM PST Thu Nov 14 2024

Moderate to large swell continues through today into Saturday,
with the latest buoy observations showing swell waves 12-13 feet
high at 12-14 seconds. A High Surf Advisory is in effect through
11 AM Saturday due to waves up to 12-15 feet, up to 18 feet along
northwest facing beaches.

King tide season is here and will bring high tides up to 1-1.5 ft
above normal today - Monday. The late morning tide cycle will be
the one to watch, especially for exposed ocean beaches when high
surf combines with the king tide. Areas that typically flood during
king tides will very likely flood within a couple hours before to
a couple hours after the daily highest tides. The next high tide
at San Francisco is expected on Friday at 10:04 AM, with a height
of 6.95 feet.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 4 PM PST Monday for CAZ006-506-508.

     High Surf Advisory until 11 AM PST Saturday for CAZ006-505-509-
     529-530.

     Freeze Warning from midnight Friday night to 8 AM PST Saturday
     for CAZ504-506-516-518.

     Frost Advisory from midnight Friday night to 8 AM PST Saturday
     for CAZ517-528.

PZ...Small Craft Advisory until 9 PM PST Friday for Mry Bay-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 Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from midnight Friday night to 3 AM PST
     Saturday for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory until 3 PM PST Friday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Gale Warning from 3 PM to 9 PM PST Friday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from midnight Friday night to 8 AM PST
     Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...SO
MARINE...SO

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea