Guerneville, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

809
FXUS66 KMTR 240020
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
420 PM PST Tue Dec 23 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 219 PM PST Tue Dec 23 2025

 - Make final preparations for strong winds this afternoon.
   Conditions deteriorate rapidly this evening.

 - Hazardous, damaging winds arrive this evening and continue
   into Wednesday morning. A High Wind Warning is in effect along
   the coast with a Wind Advisory across the interior.

 - Flood watch in effect across the area through Friday evening.
   The main hazard is flash flooding from high rain rates.

 - A slight chance of severe thunderstorms with strong wind gusts
   late Tuesday through Thursday with the potential to continue
   into Friday. Severe threats include damaging wind gusts and
   possible tornados.

 - Dangerous beach and marine conditions anticipated late Tuesday
   through Friday for all Pacific Coast Beaches

&&

.SHORT TERM...
Issued at 219 PM PST Tue Dec 23 2025
(This evening through Wednesday)

The short term threats are wind, severe thunderstorms, and
flooding, in that order. Southerly winds are picking up as a
rapidly intensifying low pressure system over the Eastern Pacific
barrels towards Northern California. The 18Z OPC analysis pegged
the central pressure at 1001 mb with an expected drop into the
980s over the next 24 hours as the system moves towards the CA/OR
border. This pressure fall will create a tight gradient with
higher pressure over the desert SW, generating sustained gale
force winds over the far Eastern Pacific and along the coast
tonight. The wind direction will gradually shift from SSE to SSW
as the low continues north. This will line up with the coastal
terrain, enhancing a southerly coastal jet. The 925mb winds look
to peak at a remarkable 70 kts right along the coast around
midnight before a front moves through and the wind speed decreases
steadily through the morning. This should translate to widespread
gusts of 60 mph along the coast, with 50 mph inland. Winds will
also be enhanced in any valleys that line up with the wind
direction. For example, the Salinas airport is already gusting to
40 kts, well ahead of the peak of the event. All indications are
that the winds will quickly subside through the morning hours
before we catch a brief break through the day Wednesday.

As the associated cold front moves through there is also a slight
chance for thunderstorms on either side of the boundary. With the
intense low level jet enhancement, any storms that form could
become severe. The main threat is damaging winds and tornados.
This is a high shear, CAPE set-up with low topped rotating storms
possible. The CAPE doesn`t break 200 J/kg, but the 0-6km shear
gets above 80 kts after the surface front moves through. A good
portion, perhaps 50% of that is in the lowest 0-1km, helping to
support tornadogenesis if any of the convection can become
surface based. SPC has expanded the marginal risk of severe
thunderstorms overnight to include the entire coast down to Pt.
Conception.

Finally this system will also bring heavy, but relatively short
duration, rainfall. The flood watch remains in effect, but it`s
less of a multi-day, widespread river flooding concern, and more
of a high rain rate flash flood concern. Fortunately the cells
will be moving very fast, so there will have to be a few in a row
to cause any real concern. By the time the sun comes up we should
just be dealing with scattered showers and limited flooding
concerns.

&&

.LONG TERM...
Issued at 210 AM PST Tue Dec 23 2025
(Wednesday through Monday)

Impacts from the initial Tuesday night to Wednesday morning system
will decrease by late morning, but, a second potentially more
impactful system will arrive late Wednesday and continue through
Friday. This second system will follow a similar path as the first
with rapid deepening expected as it moves northwards, parallel to
the California coastline. This will bring another round of strong,
impactful winds with it but wind gusts will be slightly weaker than
they were compared to the first system. Multiple rounds of moderate
to heavy rain will move through the Bay Area and the Central Coast
with this system. The WPC has issued a slight risk of excessive
rainfall for much of our area Wednesday and a marginal risk of
excessive rainfall for the Big Sur coastline on Thursday. Given the
more widespread moderate to heavy rain for this system, flooding
will be more likely across urban areas with rises in smaller
streams/creeks and mainstream rivers likely (especially the Russian
River and Napa River). With the return of moderate to heavy rain and
strong winds, additional power outages and downing of trees is
expected Wednesday night into Thursday.

The biggest threat late Wednesday through Friday will be the
potential for severe weather, including the risk of weak tornadoes
and waterspouts. The SPC has issued a marginal risk of severe
thunderstorms and a 2% chance of tornadoes/waterspouts along our
entire coastline. The highest risk for a weak tornado/waterspouts
will be from embedded thunderstorms within the main rain band as the
cold front passes through our CWA. That being said, guidance shows
the potential for isolated cells to develop in the wake of cold
frontal passage which also display potential for severe thunderstorm
development and rotation. This system looks even more favorable than
the first system with much more instability (higher MUCAPE values
over a much larger area) and continued strong low level shear
between 30 to 45 knots. A marginal risk of severe thunderstorms
continues for the Big Sur coastline into Friday while the rest of
our region has general thunderstorms. The highest potential for
thunderstorms would be along the coastline in the late morning to
afternoon timeframe with the potential for a weak tornado or
waterspout continuing. Make sure you have multiple ways to receive
any warnings that may be issued during both the Tuesday-Wednesday
and late Wednesday-Friday systems in the event that severe
thunderstorms are able to develop. This is the most favorable
environment for severe weather that we have seen in quite a while.

Rain showers continue into Friday before diminishing heading into
the weekend. This does not mean the storm door is closing with long
range guidance showing the potential for additional systems late
December into early January.

&&

.AVIATION...
(00Z TAFS)
Issued at 416 PM PST Tue Dec 23 2025

A few light showers are scattered across the Bay Area with
generally VFR ceilings regionally. Winds undergo a dramatic
increase late this evening as a strong low pressure system moves
up the coast. Most terminals will have gusts at the surface above
30 kts with strong speed shear likely as the low level jet moves
through in the pre-dawn hours Wednesday morning. This storm will
also bring a period of moderate rain with heavy downbursts
possible at times. Winds will start to ease mid-morning Wednesday
before another push of wind, rain, and a better chance for
thunderstorms move through starting Wednesday evening and
continuing through Thursday. Some of these thunderstorms could be
strong to severe with damaging wind gusts and isolated tornadoes
as the primary hazards.

Vicinity of SFO...Strong winds aloft will likely cause impacts
from low level wind shear before the main event this evening.
Strong southerly surface winds will peak around 12Z. The main band
of precipitation looks confined to 09Z-12Z, with showers possible
on either side. This upcoming storm will quickly clear out
Wednesday morning as the rain stops and winds ease. The break
won`t last long as another push of impactful weather moves
through starting Wednesday evening. Thursday morning looks like a
better chance for thunderstorms at the moment.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Southerly winds will increase through the
afternoon, particularly at SNS where the wind direction lines up
with the Salinas Valley. Very strong winds are expected early
Wednesday morning, when SNS may gust to a rare 50 kts. The band
steady rain and possible thunderstorms will move through from
around 08Z to 14Z.

&&

.MARINE...
(Tonight through next Monday)
Issued at 416 PM PST Tue Dec 23 2025

EXTREMELY HAZARDOUS MARINE CONDITIONS EXPECTED TUESDAY NIGHT.
Conditions will quickly deteriorate over the next 6 hours as a
significant, storm-force low pressure system traverses the waters.
Widespread sustained gale force southerly winds will arrive
tonight with frequents gusts near 60 kts in exposed waters. These
winds will build very rough, steep waves with a significant wave
height near 20 feet. A brief reprieve will arrive Wednesday before
conditions deteriorate again Wednesday night. If your vessel is
not able to handle these conditions return to port or seek
protected waters as soon as possible.

&&

.BEACHES...
Issued at 429 AM PST Tue Dec 23 2025

The strong winds along the coast will result in hazardous beach
conditions. A Beach Hazards Statement has been issued for the
coast from 4PM Tuesday through 4AM Wednesday. The main concerns
include:blowing and drifting sand and wind waves up to 20 ft. The
drifting sand and increased sea spray will also result in poor
visibilities, affecting water rescues. Increased coastal erosion
will be possible as well.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch through Friday evening for CAZ006-502>506-508>510-
     512>518-528>530.

     Beach Hazards Statement until 4 AM PST Wednesday for CAZ006-505-
     509-529-530.

     High Wind Warning until 4 AM PST Wednesday for CAZ006-502-503-
     505-509-516-517-528>530.

     Wind Advisory until 4 AM PST Wednesday for CAZ504-506-508-510-
     512>515-518.

PZ...Gale Warning until 3 AM PST Wednesday for SF Bay N of Bay Bridge.

     Gale Warning from 3 PM Wednesday to 3 AM PST Thursday for SF Bay
     N of Bay Bridge.

     Gale Warning until 9 PM PST this evening for Mry Bay.

     Storm Warning from 9 PM this evening to 3 AM PST Wednesday for
     Mry Bay.

     Storm Warning until 3 AM PST Wednesday 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.

     Storm Warning until 3 AM PST Thursday for Pigeon Pt to Pt Pinos
     0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Flynn
LONG TERM....Kennedy
AVIATION...Behringer
MARINE...Behringer

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