Clayton, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

624
FXUS66 KMTR 232155
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
155 PM PST Mon Dec 23 2024

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

.SYNOPSIS...
Issued at 155 PM PST Mon Dec 23 2024

Very hazardous beach conditions will continue through Tuesday, as
high surf impacts the coast and potentially leads to coastal
erosion and flooding. Next storm system takes aim at the region
late tonight and into Tuesday, with widespread rain and isolated
thunderstorms possible. Gusty south to southwest winds will also
develop tonight, with gusts up to 40 mph possible, before shifting
to the west on Tuesday post-frontal. Although dry weather will
prevail for Christmas, more wet and unsettled weather will return
for Thursday through early next week.

&&

.SHORT TERM...
(This afternoon through Tuesday)
Issued at 155 PM PST Mon Dec 23 2024

Key Messages:
*High Surf continues to build along the coast, leading to
 coastal erosion and coastal flooding.
*Life-threatening beach and ocean conditions linger into through
 the week.
*Series of storm systems to continue through next week.
*Most impactful storm appears to be late tonight into Tuesday.
*Rainfall totals between now and Sunday evening: North Bay
 Valleys: 1.5-3.5 | North Bay Mountains 3-8" | Bay Area:
 1-3" | Central Coast: 1-3" | Salinas Valley: Up to 1"
*Wind gusts up to 40 mph (isolated 45 mph in spots) on Monday
 night into Tuesday.

Water vapor imagery shows the weak warm front spreading over
Northern California this afternoon, with radar imagery showing
some light returns mainly north of I-80 at this time. Santa Rosa
has been reported light rain and fog on and off today, and this
trend will continue through this evening. Meanwhile, areas south
are seeing filtered sun. As a result, temperatures are warming
into the mid and upper 60s, with a few locations in the lower 70s.
This is 5 to 10 degrees above normal for this time of year.

Main concern for today continues to be with the building surf and
coastal flooding. All coastal buoys are seeing significantly
higher wave heights than the models were indicating for this event,
with the surf continuing to build at this time. Therefore, the
High Surf Warning has not only been increase in heights, but
extended as it will take time for the swell to wave. There is a
lot of water moving out there, and we are just beginning to see
the impacts. If you are headed out to the coast today, stay off
the rocks, jetties, and beaches, as these large breaking waves can
sweep across the beach without warning.

Scattered light rain will continue across North Bay through this
evening, then become more widespread late tonight and into
Tuesday, as the cold front spreads across the region. Rain will
spread north to south across the region, making for a messy
commute tomorrow morning for those that have to work or are
traveling on Christmas Eve. There is enough instability with this
system, that there is a slight chance of thunderstorms possible
as well. While this rain will mostly be beneficial for the region,
North Bay will once again see the brunt of the rainfall. Given
the wet weather and moist antecedent conditions, believe streams
and creeks will rapidly rise once again. For now, the forecast
remain below flood stage, so we will need to watch them closely.

Other lesser concerns with this system are with the winds. That
said, breezy south southwesterly winds will develop late tonight
and into Tuesday morning, as 925 mb and 850 winds increase to 25
to 35 kts, before shifting to westerly behind the front. At this
time, cannot rule out some gusts up to 45 mph, but do not see the
need for widespread wind products. That said, with the saturated
soils, even a gust to 45 mph could down a tree. Palmer

&&

.LONG TERM...
(Tuesday night through next Sunday)
Issued at 155 PM PST Mon Dec 23 2024

Drier condition will develop in the wake of this system, with
foggy conditions likely (60%) developing in the valleys for
Christmas Eve and Christmas morning. Temperatures will also fall
back into more normal ranges for Christmas Day.

That said, wet and unsettled weather returns overnight Wednesday
and into Thursday, and will continue through the weekend, as a
series of storms take aim at Northern California. For the most
part, the storm track looks like it will be primarily north of us,
such that the Bay Area and Central Coast will be on the southern
fringes of the rain. As a result, North Bay still looks like they
will see the greatest totals for the region, but even for the North
Bay, the amounts are trending less and less. In fact, storm
totals through Sunday have backed off so much that areas south of
I-80 will be lucky to see upwards of an inch total when all is
said and done. Palmer

&&

.AVIATION...
(18Z TAFS)
Issued at 1128 AM PST Mon Dec 23 2024

Areas improve to MVFR-VFR this afternoon with passing mid to high-
level clouds. Winds remain generally light through the day. Pre-
frontal showers build in the North Bay into the evening with
lowering CIGS. The main frontal rain band arrives in the North Bay
early Tuesday morning bringing moderate rains and breezy to gusty
winds, lowering visibilities. CIGS lift in the post-frontal
environment as winds turn more westerly. Showers linger behind the
front with isolated storm chances until the late afternoon.

Vicinity of SFO...IFR CIGS last into the evening before becoming
MVFR. Expect light showers to arrive into the night followed by the
main rain band into early Tuesday. Gusty west winds move into the
area along the moderate rains, leading to reductions in visibility.
Expect winds to reduce into the late morning as the rain band exits,
with lingering shower activity into the afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR lasts into the early night before MVFR
CIGS build into the area. Winds stay light to moderate through the
day and into the night. Light rains and lowers CIGs arrive in the
late night ahead of the front. CIGS rise, but visibilities fall as
the main rain band enters the area in the mid morning. Breezy to
gusty west winds will come along with the front and last into the
afternoon.

&&

.MARINE...
(Today through Saturday)
Issued at 855 AM PST Mon Dec 23 2024

A very large westerly swell is arriving and will persist into
Tuesday, with only slight reductions into Wednesday. Expect
dangerous conditions for small crafts through much of the week.
Elevated seas will continue to produce enhanced shoaling at harbor
entrances and bars.

&&

.BEACHES...
Issued at 155 PM PST Mon Dec 23 2024

A High Surf Warning is now in effect through 6 pm Tuesday for
breaking waves 30 to 40 feet, with some of the favored spots
potentially experiencing up to 60 foot breaking waves.

The Point Reyes and Point Sur buoys are showing significantly
higher wave heights than the wave models were indicating at this
time. In fact at 20z, Point Reyes reported a wave heights of
23.56 feet, and Point Sur reported a wave height of 25.89 feet.
Even Soquel Cove South Buoy is reporting at wave height of 18.57
ft at 2030z. Therefore, the High Surf Warning has been updated to
reflect current thinking of surf heights, and extended through 6
pm on Tuesday as it will take time for the swell heights to come
down.

The Coastal Flood Warning also remains in effect to address the
potential for impacts to coastal locations such as piers, wharfs,
and other structures along the coastline. Flooding/inundation of
roads, parking lots, and coastal trails can also be anticipated.
These conditions will result in dangerous and life-threatening
bay, ocean, and beach conditions through Tuesday. Beyond Tuesday,
swell heights will begin to diminish, but favorable conditions for
hazardous surf conditions remain into the next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Warning until noon PST Tuesday for CAZ006-505-509-
     529-530.

     High Surf Warning until noon PST Tuesday for CAZ006-505-509-529-
     530.

PZ...Small Craft Advisory from 9 PM this evening to 3 PM PST Tuesday
     for SF Bay N of Bay Bridge.

     Small Craft Advisory until 9 PM PST Tuesday for Mry Bay-Pigeon
     Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 PM PST Tuesday for 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 AM PST Wednesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Palmer
LONG TERM....Palmer
AVIATION...Murdock
MARINE...Murdock

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