317
FXUS66 KMTR 121641
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
841 AM PST Wed Feb 12 2025

...New UPDATE, MARINE...

.SYNOPSIS...
Issued at 111 AM PST Wed Feb 12 2025

The precursor rain event continues through the morning south of the
Golden Gate. A more intense system brings the risk for flooding and
damaging winds through Thursday. A Flood Watch for the coastal
counties and a High Wind Watch for the entire region come into
effect at 10 PM tonight. The storm system clears out late Thursday
and Friday with drier conditions going into the weekend.

&&

.UPDATE...
Issued at 819 AM PST Wed Feb 12 2025

Current radar showing some elevated showers moving in over the
waters associated with a warm front extended along the CA coast.
The surface low is currently about 1,000 mi to our NW at a
central surface pressure of 992 mb, and is expected to rapidly
deepen over the next several hours to about 981 mb as it moves to
the SE. Still looking at a time of arrival of about 7 PM this
evening for the heavier rain for the North Bay and SF areas, a few
hours later for the rest of the Bay Area and Central Coast.
Heaviest rain rates after midnight pretty much across the board.
Flood and High Wind Watches will be evaluated later this morning
for potential areas added (flood) and upgrade to warning (wind).

Behringer

&&

.SHORT TERM...
(Today and Thursday)
Issued at 111 AM PST Wed Feb 12 2025

KEY POINTS

* Precursor rainfall event continues early this morning, more
  impactful event Wed PM/Thu AM
* Flood Watch in effect 10 PM Wed to 10 PM Sat (coastal counties)
* High Wind Watch in effect 10 PM Wed to 10 AM Fri (entire CWA)
* Soils saturated after initial rain Wednesday, widespread shallow
  landslides, downed trees
* Highest impact Santa Cruz Mtns, Big Sur Coast
* High Surf Warning in effect 3 PM Thu to 3 AM Sat (Pacific Coast)

Radar returns and satellite imagery reveal widespread light
rainfall, with some regions of heavier rain rates, impacting the
region south of Marin County and the Carquinez Strait down through
the Central Coast. Rainfall totals have remained relatively modest,
with accumulations of a tenth to a quarter of an inch across the
coastal regions and a few hundredths of an inch inland. Up to half
an inch of additional rainfall is expected across the Santa Lucias,
with generally around a tenth to a quarter inch of additional
rainfall expected in the Monterey Bay and Salinas Valley regions.
This additional rainfall is expected to fall before sunrise across
most of the region, with the southern half of Monterey County
remaining rather showery into the late morning hours. As the first
hit of rain moves out, today should be rather dry but cloudy, with
high temperatures reaching the middle to upper 50s for most of the
lowlands (except the North Bay coast where highs reach the low 50s).

The next storm system begins to impact the region Wednesday night,
as a deep upper level low rapidly develops off the Pacific Northwest
while a surface low strengthens to around 984 mb off Northern
California. (Peak intensification is currently forecast for around
16 mb in 24 hours, around 2-3 mb short of the bomb cyclone criteria
for a cyclone at 42N latitude, which is where the cyclone is
expected to develop.) An intense rain band is expected to develop in
the North Bay late tonight into early Thursday morning, and spread
into the Central Coast by sunrise. Given ample upper level support
from the left exit region of a 150 kt jet streak, which favors
strong rising motion in the atmosphere, rainfall rates in this
intense band will rise to 0.8 to 1.2 inches per hour. The greatest
impacts from these intense rain rates are currently expected in the
Santa Cruz and Santa Lucia ranges, but we can`t rule out brief
intense rain along the North Bay coastal ranges and San Francisco.

A Flood Watch has been issued for the coastal counties of
Sonoma, Marin, San Francisco, San Mateo, Santa Cruz, and Monterey,
in effect from 10 PM Wednesday to 10 PM Saturday. When all is said
and done, most inland locations can expect 1.5 to 2.5 inches, less
in rainshadowed valleys, and 3 to 6 inches in the Santa Cruz Mtns
and Big Sur coastal range. In addition, soils around the Bay Area
will be sufficiently saturated after tonight`s rainfall to support
widespread shallow landslides Thursday morning in areas that see the
higher end rain rates. Use caution on roadways and near steep
slopes.  Current areas of most concerns for river flooding are the
Russian River near Guerneville and Mark West Creek, as well as the
San Lorenzo River in Santa Cruz county. Otherwise, urban and small
stream flooding will almost certainly be an issue elsewhere
throughout the Flood Watch area.

In addition to the rainfall, damaging winds are expected with the
system, particularly along the coast and the ridgetops, with a High
Wind Watch issued for the entire forecast region from 10 PM
Wednesday to 10 AM Friday. Widespread gusts up to 60 mph range are
possible, with potential gusts in the 70-80 mph range across the
immediate coastline and the ridgetops on the coastal ranges. The
combination of saturated soils and high winds will result in the
increased possibility of downed trees and powerlines, leading to
further damage and/or power outages. There is also a slight chance
for thunderstorms Thursday afternoon as colder air moves in aloft
and some clearing allows for more surface heating and consequently a
more unstable atmosphere. Outside of locally heavy rainfall and
gusty winds, as well a few lightning strikes, no other severe
hazards are expected. Nearly straight hodographs with little low
level directional shear don`t support much in the way of rotating
updrafts. An exception would be along the coast near Point Reyes and
the Sonoma coast where the lower level shear profile is a bit more
favorable to support a brief waterspout or two.

&&

.LONG TERM...
(Thursday night through Tuesday)
Issued at 111 AM PST Wed Feb 12 2025

The surface low moves onshore late Thursday night, bringing an end
to the widespread rain and wind. Friday and Saturday look to be
mostly dry with a few lingering showers possible early on Friday. A
dissipating shortwave comes into the Pacific Northwest on Sunday,
bringing slight rain chances to the North Bay. CPC outlooks show a
lean towards temperatures above seasonal averages and precipitation
below seasonal averages for the second half of February.

&&

.AVIATION...
(12Z TAFS)
Issued at 353 AM PST Wed Feb 12 2025

Currently VFR at all terminals. Conditions will significantly
deteriorate through the TAF cycle as widespread MVFR conditions
are expected with further deterioration to IFR possible with the
heaviest of rain showers. Winds will be a bit squirrelly this
morning, but a stark wind shift is expected this evening to a
southerly regime. Expect cloud decks to lower throughout the day
with rain beginning this afternoon, increasing in coverage and
intensity though the night. There is also a slight risk for
thunderstorms beginning Thursday morning.

Vicinity of SFO...Currently VFR with light southwesterly winds. Once
strong enough to have a prevailing direction, winds will prevail out
of the east through the afternoon. A shift to southerly winds is
expected by 23Z with winds strengthening overnight with gusts up to
34 knots to be expected with the timeframe of biggest concern
being 08Z-12Z Thursday. Rain will impact the terminal by 03Z with
intensities increasing overnight. Low level wind shear has been
included in the TAF at 12Z Thursday as winds at the surface are
expected to quickly diminish while winds aloft are expected to
remain strong.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with easterly flow at MRY and
VFR with drainage flow at SNS. Winds will be somewhat variable this
morning ahead of southeasterly winds that are expected this evening.
Light rain will begin to impact the terminals this afternoon with
moderate to heavy rainfall on tap for tonight through tomorrow
morning.

&&

.MARINE...
(Today through Monday)
Issued at 819 AM PST Wed Feb 12 2025

Southwest winds increase through the day with widespread gale
conditions expected into the night with isolated storm force
gusts possible. Moderate period westerly swell will build through
Friday morning with very rough to high seas expected. Light rain
showers will continue through the day ahead of moderate to heavy
rainfall that is expected Wednesday night through Friday morning
with a slight chance for thunderstorms Thursday.

&&

.BEACHES...
Issued at 1101 PM PST Tue Feb 11 2025

A High Surf Warning is in effect from 3 PM Thursday through 3 AM
Saturday for all Pacific Coast beaches. Westerly swell with a period
up to 15 seconds will build through Friday. As a result, west-facing
beaches will see dangerously large breaking waves of 20 to 30 feet
and up to 45 feet peak waves, non-west facing beaches will see
dangerously large breaking waves of 15 to 20 feet and up to 30 feet
peak waves. Everyone should remain out of the water due to life-
threatening surf conditions. Stay off of jetties, piers, and other
waterside infrastructure, keep pets on a leash and away from the
water, and never turn your back on the ocean!

Sarment

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from this evening through Saturday evening for
     CAZ006-502>506-508-509-512-516>518-528>530.

     High Wind Watch from this evening through Friday morning for
     CAZ006-502>506-508>510-512>518-528>530.

     High Surf Warning from 3 PM Thursday to 3 AM PST Saturday for
     CAZ006-505-509-529-530.

PZ...Gale Warning from 9 PM this evening to 3 PM PST Thursday 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 Reyes to Pigeon Pt 0-
     10 nm-SF Bay N of Bay Bridge.

     Small Craft Advisory from 3 PM this afternoon to 9 PM PST this
     evening for 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 Reyes to
     Pigeon Pt 0-10 nm.

     Gale Warning from 3 PM this afternoon to 3 PM PST Thursday for
     Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory until 3 PM PST this afternoon for Pt Arena
     to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Behringer/DialH
LONG TERM....DialH
AVIATION...Sarment
MARINE...Murdock

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