San Geronimo, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

323
FXUS66 KMTR 221039
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
239 AM PST Sun Dec 22 2024

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

.SYNOPSIS...
Issued at 229 AM PST Sun Dec 22 2024

A parade of systems will bring compounding impacts to the Bay Area
and Central Coast. Life-threatening bay, ocean, and beach conditions
linger through next week.

&&

.SHORT TERM...
(Today and tonight)
Issued at 229 AM PST Sun Dec 22 2024

Light rain can be expected today thanks to a weak frontal boundary
across Central California which will allow for precipitation up to
0.25" in orographic lift favored locations like the East Bay
Hills, Eastern Santa Clara hills, Santa Cruz Mountains, and the
Santa Lucia Mountains. A cold front will move through tonight
providing another shot of rainfall with totals on the order of
0.25"-0.75" for the North Bay, up to 0.25" for the rest of the Bay
Area, with drizzle at best in Monterey and San Benito Counties.

A High Surf Warning will replace the High Surf Advisory at 4 PM with
life-threatening beach and ocean conditions lingering into next
week.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 229 AM PST Sun Dec 22 2024

Key Messages:
*Parade of storm systems through next week
*Most impactful storm appears to be Monday into Tuesday
*Rainfall totals between today and Saturday: North Bay: 2"-6",
 locally up to 9", rest of the Bay Area: 1-4", Central Coast:
 0.25"-1.50", locally up to 5" in the Santa Cruz Mountains and
 locally up to 3" along the Big Sur Coast
*Wind gusts up to 45 mph on Tuesday
*Life-threatening beach and ocean conditions linger into next week.

A widespread impactful system will move through the region Monday
afternoon through Tuesday afternoon. Rainfall totals up to 2.50" are
forecast for the higher terrain of the North Bay with a gradual
taper in rainfall amounts from north to south with higher rainfall
totals expected in higher terrain. The greatest impacts are expected
in the North Bay as portions of Marin, Napa, and Sonoma Counties
have been highlighted by the Weather Prediction Center (WPC) for a
marginal/at least 5% risk of rainfall exceeding flash flood guidance
between 4 AM Monday and 4 AM Tuesday. This means that isolated flash
floods will be possible and that their nature will be localized and
primarily affecting places that can experience rapid runoff with
heavy rainfall. Fortunately, no mainstem river forecast points are
forecast to reach minor flood stage according to deterministic
forecasts; however, rivers and their creeks and streams will have no
problem responding quickly to rainfall. While it is too early to
issue any wind headlines, there is increasing probability of wind
gusts reaching or exceeding 45 mph during this system. Whether
southerly winds meet Wind Advisory criteria or not, soils
approaching saturation in addition to tree damage from last
weekend`s storms will allow for plentiful tree debris. Isolated
thunderstorms will also be possible with this system with the Storm
Prediction Center (SPC) highlighting all counties with the exception
of Monterey and San Benito for general or non-severe thunderstorms
between 4 AM Tuesday and 4 AM Wednesday. Remember
that lightning and flooding threats exist with all thunderstorms. An
ECMWF point sounding forecast for STS at 10 AM Tuesday shows that
the environment will be that of low CAPE and high shear, but that
the parcel will have to overcome a stable lapse rate in the
850-700 mb layer.

Wednesday will be dry, giving rivers and their creeks and streams in
addition to soils a chance to somewhat dry out ahead of more
rainfall.

Another cold front moves through the region Thursday bringing
rainfall totals of up to 1.00" in the higher terrain of the North
Bay with a stout tapering of rainfall totals from north to south
with interior Monterey and San Benito County not expecting to
receive any rainfall. Friday and beyond is unfortunately where
confidence begins to wane. Global ensemble clusters are depicting
the potential for zonal flow across much of the region which would
deflect systems to the north of the region; however, there may be
just enough troughiness over the North Bay to allow for more
impactful rainfall with the help of some shortwave troughs.

&&

.AVIATION...
(06Z TAFS)
Issued at 945 PM PST Sat Dec 21 2024

KMUX radar shows light rain arriving from the west. The terminals
are currently reporting MVFR-LIFR. Patchy fog is also likely tonight
and Sunday morning. Otherwise wet weather tonight and Sunday morning
with lingering showers Sunday, greater areal coverage of wet weather
returning Sunday night and early Monday morning.

Vicinity of SFO...IFR tonight and Sunday morning with periodic
light rain. Light rain returning Sunday night and early Monday
morning. Light northerly to easterly wind during the period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR-IFR, vicinity showers tonight and
Sunday morning. Mainly light easterly winds.

&&

.MARINE...
(Today through Friday)
Issued at 229 AM PST Sun Dec 22 2024

Large, building westerly swell continue into Sunday morning with
a temporary decrease in swell later Sunday. Then, a large to very
large westerly swell is expected Monday into Tuesday. Wave
heights will remain elevated through late next week with 15 to 20
foot waves Monday through Wednesday. Expect dangerous conditions
for small crafts through the weekend and into midweek. Elevated
seas will continue to produce enhanced shoaling at harbor
entrances and bars.

&&

.BEACHES...
Issued at 111 PM PST Sat Dec 21 2024

High surf advisory remains in effect through Sunday afternoon for
elevated surf of 20-25 feet, with breakers up to 30 feet. A long
period, westerly swell will continue to create hazardous beach
conditions along the coast into Tuesday. Global wave models are
forecasting a more intense energetic swell with 20+ feet heights and
swell periods of 20+ seconds, this will lead to much higher breakers
(possibly 30-35 feet) including localized coastal flooding impacts.
These conditions will result in dangerous and life-threatening bay,
ocean, and beach conditions lingering into next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 4 PM PST this afternoon for CAZ006-505-
     509-529-530.

     High Surf Warning from 4 PM this afternoon to noon PST Tuesday
     for CAZ006-505-509-529-530.

PZ...Small Craft Advisory until 3 AM PST Tuesday for Mry Bay-Pigeon
     Pt to Pt Pinos 0-10 nm-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-Pt Reyes to Pigeon Pt 0-
     10 nm.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...RGass

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