Saint Helena, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

658
FXUS66 KMTR 142337
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
337 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.

&&

.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...
(00Z TAFS)
Issued at 337 PM PST Thu Nov 14 2024

Satellite shows mostly VFR ceilings, but MVFR/IFR ceilings have
developed along Monterey Bay. Light showers will continue into the
night, but ceilings should remain VFR after low ceilings dissipate
near the Monterey Bay terminals. Post-frontal environment will
produce some moderate to breezy winds overnight. Onshore winds
continue to build by Friday afternoon and will become gusty with
speeds up to 26 knots. Some models hint at low ceilings developing
over North Bay late overnight/early Friday morning, but very low
confidence to include in TAFs at this moment.

Vicinity of SFO...VFR with a FEW/SCT low stratus over the terminal.
Ceilings will build into the night and is anticipated to remain VFR
heights through the TAF period. Expect some light vicinity showers
overnight. Moderate onshore winds will build to breezy/strong and
gusty overnight, with moderate confidence when winds will ease back
to moderate or light.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR/IFR conditions have developed but
overall VFR ceilings should return after 02Z. Low to moderate
confidence that ceilings will lower again through the night, but
model show agreement of VFR prevailing after 02-03Z. Winds will
start to build towards Friday afternoon, with moderate chance for
gusty winds up to 24 knots.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 337 PM PST Thu Nov 14 2024

Isolated light showers continue to move through the waters but
are gradually diminishing. 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. 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 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.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...SO
MARINE...SO

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