St Helena, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

762
FXUS66 KMTR 230536
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
936 PM PST Fri Nov 22 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 200 PM PST Fri Nov 22 2024

Widespread moderate to at times heavy rainfall continues over the
SF Bay Region as the main rain band continues to stall through
this afternoon/evening. Prolonged rainfall will result in an
increased risk of flooding, an increased risk of landslides, and
downed trees and powerlines. Stay weather aware and have a way to
receive warnings.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 200 PM PST Fri Nov 22 2024

Key Messages:

- A moderate risk of excessive rainfall continues for North Bay,
while a slight to marginal marginal risk continues for the rest of
the Bay Area.
- Moderate to heavy rain has spread into the SF Bay region with
widespread flooding reported across the North Bay, city of San
Francisco, San Francisco Peninsula, and East Bay.
- Flooding impacts will increase throughout the SF Bay region as the
main rain band looks to stall over it for much of the day. The band
will gradually progress southwards late this afternoon/evening but
forward progress will be slow.
- Saturated grounds in the North Bay are leading to an increased
risk of landslides.
- River and creek flooding continues across the North Bay with
many rivers and creeks either above or set to rise above flood stage.
- Strong, gusty southerly winds continue through late tonight and
will be most intense ahead of and along the front. Widespread gusts
up to 50 mph are expected with 60+ mph gusts possible above 2,500
feet.

Intense, moderate to heavy rainfall has progressed into the San
Francisco Bay region and is expected to slowly spread southwards
this afternoon and evening. Widespread flooding is expected as the
AR looks to stall over the SF Bay region through the
afternoon/evening. This stall is well agreed upon by the GFS, HRRR,
and local WRF guidance which all keep moderate to heavy showers over
the SF region through 7 PM to 8 PM tonight. Guidance shows the main
band of rain tightening and becoming more progressive by late this
evening (7 PM to 9 PM timeframe). The main rain band will reach the
Central Coast at the earliest 8 PM but will more likely arrive
between 9 PM to 10 PM. The rain band will remain fairly progressive
once it reaches the Central Coast and current guidance suggests it
will be fully out of Monterey/San Benito Counties by 3 AM to 4 AM.
In the wake of frontal passage, scattered light to at times moderate
rain showers will continue with a low (less than 10% chance) of
thunderstorms developing. Precipitation totals were increased across
the SF Bay Area to account for this system stalling over the region.
As such, the San Francisco Peninsula and the East Bay are now
expected to receive 2-3" of rain Friday into Saturday with up to 4"
possible within the Santa Cruz Mountains and East Bay Hills. The
Santa Clara Valley and Central Coast will see between half an inch
to a little over an inch. As scattered showers continue through the
day on Saturday, additional accumulations up to a few tenths of an
inch are possible.

In addition to flooding concerns, a Wind Advisory remains in effect
through 10 PM tonight for widespread gusts up to 50 mph and elevated
potential for 60+ mph gusts above 2,500 feet. The combination of
intense rain and strong winds will lead to an increased risk of
downed trees and power lines across the Bay Area and Central Coast.
Winds are expected to drop off rapidly after frontal passage occurs.
There will be consideration for extending the Wind Advisory for the
southern counties depending on how fast the front moves southward.
As soils become more saturated, landslide risk will increase. This
is particularly evident in the North Bay where multiple landslides
have been reported since Wednesday.

Numerous reports of flooding have already come in across the North
Bay, San Francisco Peninsula, and East Bay which has triggered
additional Flood Warnings (North Bay), Flood Advisories (San
Francisco Peninsula and East Bay), and a Flash Flood Warning (City
of San Francisco - in effect through 3:15 PM). Flooding impacts are
expected to spread into the South Bay and Santa Cruz regions during
the early afternoon as the main rain band spreads southward.
Residents of the Bay Area are recommended to avoid any unnecessary
travel this afternoon/evening. While the potential for flooding is
slightly lower over the Central Coast, residents are still advised
to exercise caution and avoid any unnecessary travel as the front
moves through this evening/overnight. For those who are unable to
avoid traveling, remember to slow down while driving, allow extra
time to reach your destination, and never drive through flood

&&

.LONG TERM...
(Saturday night through next Thursday)
Issued at 200 PM PST Fri Nov 22 2024

Rainy weather will continue through mid next week with scattered,
showers to bring an addition 0.5" to 2" across the Bay Area through
early next Wednesday. Monday into Tuesday, a weak low pressure
system looks to move inland into the Central Coast and bring with it
our next chances for rain. That being said, both Euro and GFS
precipitable water guidance keep higher PWAT values concentrated
across the Central Coast and southern California. If this trend
continues, this may be more of a Central Coast/southern California
system. All together, precipitation totals across the Central Coast
will be between 1" to 2" while the Santa Lucias will see between 2"
to 3" Sunday through early Wednesday. Widespread drier conditions
look to return late Wednesday into Thursday but some uncertainty
remains due to model differences in where ridging/troughing will set
up. CPC continues below normal to near normal temperatures through
the beginning of December.

&&

.AVIATION...
(06Z TAFS)
Issued at 935 PM PST Fri Nov 22 2024

Showers continue across our region but heavier rain bands have moved
southward over Monterey Bay creating a mix of VFR, MVFR, IFR, and
LIFR conditions. Conditions are starting to improve a bit over North
Bay, but there is some uncertainty if conditions will deteriorate
overnight. Models show some disagreement when VFR will predominately
return but some models suggest as early as 09Z-12Z for SF Bay, East
Bay, and South Bay terminals. There is moderate confidence that VFR
will return for the remaining terminals near 12-14Z, with higher
chances after 20Z for terminals further south. Southerly winds are
starting diminish over the North Bay, as the remaining terminals are
still experiencing breezy conditions. Some terminals near the
gaps and passes are seeing some gusty winds but should shortly
decrease. Overnight winds will diminish to a light to moderate
speed.

Vicinity of SFO...MVFR with occasional IFR conditions. Conditions
are expected to improve to VFR by 09Z but some model solutions show
as late as 12-14Z. There is uncertainty concerning wind direction
and speed. Currently winds are W, but most models show the southerly
winds will continue until 09-10Z. With higher confidence that winds
will remain westerly, relatively breezy westerly winds were placed
in the TAFs. Overall light to moderate speeds overnight through the
rest of the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR with some light rain. Ceilings may
lower to MVFR throughout the night, but confidence is moderate as
some models suggest VFR through the TAF period. If MFVR ceilings
develop overnight expect VFR to return after 18-19Z. Southerly winds
have build to strong and gusty over KSNS but KMRY is currently
calm.

&&

.MARINE...
(Tonight through next Thursday)
Issued at 935 PM PST Fri Nov 22 2024

Hazardous marine conditions continue into Saturday with strong
wind gusts continuing for Pacific waters south of the Farallons.
Significant wave height of 7 to 10 feet continue into the night
before easing down to 5 to 8 feet on Saturday. Seas will rebuild
briefly late Sunday and into early Monday. Boating conditions will
improve this weekend, but still remain quite hazardous,
particularly to smaller vessels and crafts.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 10 AM PST Saturday for CAZ006-509-512-514-
     515-517-518-530.

     Flood Watch through Saturday morning for CAZ502>506.

PZ...Small Craft Advisory until 3 AM PST Saturday for Mry Bay-Pigeon
     Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10
     nm-SF Bay N of Bay Bridge.

     Small Craft Advisory until 9 AM PST Saturday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...SO
MARINE...SO

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