308
FXUS66 KMTR 221303
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
503 AM PST Fri Nov 22 2024

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

.SYNOPSIS...
Issued at 453 AM PST Fri Nov 22 2024

An atmospheric river continues to inundate northern California this
morning, with the North Bay region currently seeing the bulk of the
rain. Rain chances will increase throughout the day for the service
area as a cold front works its way across the Bay Area and north
Central Coast. Prolonged rainfall will result in an increased risk
of flooding, an increased risk of landslides, and downed trees and
powerlines across the North Bay.

&&

.SHORT TERM...
(Today and tonight)
Issued at 453 AM PST Fri Nov 22 2024

Key Messages:

-Widespread moderate to heavy rain will spread southeast across
 the rest of the Bay Area and north Central Coast today.
-Large waves and strong winds will lead to dangerous marine and
 beach conditions today.
-Heavy rain may lead to the flooding of low lying areas and
 roadways, which may cause them to not be passable.
-Gusty winds, especially where soils are saturated, may lead to
 downed trees and power lines.
-Saturated grounds may lead to an increase risk of land slides.

An atmospheric river will continue to impact northern and central
California today. As of this morning, the majority of the rain has
been up in northern California reaching as far south as the North
Bay. The area of low associated with this AR spins west of the PacNW
via satellite. The Ocean Prediction Center placed the cold front
around 846UTC between 130W and 120W. This cold front is expected to
gradually work its way through the region, bringing widespread to
moderate heavy rain for the Bay Area and the north Central Coast.
Areas south of there, chances for rain decrease. Given the prolonged
rain for our northern most areas, the Weather Prediction Center has
placed the North Bay in a Moderate Risk (level 3 of 4) for
Excessive Rainfall and the rest of the Bay Area and the north
Central Coast in a Slight Risk (level 2 of 4) which matches well
with the listed flooding hazards listed above in the key points.
Elsewhere in the Central Coast, particularly for the rest of Santa
Clara, northwest San Benito, and areas along and west of the
Salinas Mountains in Monterey County, a Marginal Risk (level 1 of
4) of Excessive Rain is forecast. In addition to the rain threat,
southerly winds will increase today ahead of the cold front. The
Wind Advisory covers much of the region, where sustained wind
speeds will range from 15 to 30 mph. Gusts up to 40 to 50 mph are
expected for coastal communities and for elevations up to 2500
feet. There is a decent shot at some of the ridges above 2500 feet
seeing winds exceed 50 mph, perhaps getting close to 65 mph.
Areas that are excluded from the winds are the valley zones where
they should be sheltered from the stronger gusts. Given the
saturated grounds and increasing winds in the North Bay, there
will be an increased risk of landslides, flood roads, especially
in low lying and poor drainage areas, downed trees, and downed
powerlines. There may be a couple of rumbles of thunder,
particularly in the North Bay; however, confidence is fairly low.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 453 AM PST Fri Nov 22 2024

Wet weather continues through the weekend and into early next week.
Showers will linger across the region in wake of the cold front on
Saturday. Several additional rounds of rain will then work their way
through the region beginning on Sunday and continuing through
Tuesday as low pressure sits off the coast. The upper level trough
will slowly work through the PacNW and then enter intermountain west
by midweek. Conditions begin to dry out by then and may hold for a
day or two. There`s some split guidance in the cluster analysis as
to where ridging sets up and if an upper low forms west-southwest to
southwest of southern CA.

&&

.AVIATION...
(12Z TAFS)
Issued at 453 AM PST Fri Nov 22 2024

Impactful day at all terminals as a potent cold front sweeps through
the region.  Starting to see the next round of precip develop over
the N Bay with MVFR conditions.  This trend will continue southward
and through the morning rush.  There will likely be a period of MVFR
to IFR conditions this afternoon with the fropa. +RA will be
possible during fropa as well. Didn`t put +RA in TAF due to lower
confidence on timing and extent of +RA.  Winds will be gusty through
at least this evening.  Do expect rapid improvement overnight as the
front moves SE.  Lingering cigs and VCSH will then persist through
end of TAF.

Vicinity of SFO...MVFR with a periods of IFR (FROPA.  Wet runways
with SE winds will also be problematic for SFO.  No AWW at this
time as probs show 30-40% exceeding 35kts.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR to VFR this morning.  Will have to
wait until later this afternoon before steadier precip arrives. MVFR
most of the time, but a 30% chc for IFR with steadier rain/fropa 06-
09Z tonight.

&&

.MARINE...
Issued at 453 AM PST Fri Nov 22 2024

A potent cold front will move through the region today bringing
hazardous conditions to the coastal waters and bays. Gale force
winds with gusts up to 45 kt will be possible Friday, especially
north of Point Reyes. The strong winds will produce very steep
wind waves. The passing front will bring widespread rain and a
slight chance for thunderstorms. Mariner venturing to open waters
are urged to use caution and check conditions before leaving
shore. Boating conditions will improve this weekend, but still
remain quite hazardous, particularly to smaller vessels and
crafts.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 6 AM PST early this morning for CAZ006-
     505-509-530.

     Wind Advisory until 10 PM PST this evening for CAZ006-502>505-
     509-512-514-515-517-518-530.

     Flood Watch through late tonight for CAZ502>506.

     Beach Hazards Statement until 6 AM PST early this morning for
     CAZ529.

PZ...Small Craft Advisory until 3 AM PST Saturday for Mry Bay-SF Bay
     N of Bay Bridge.

     Gale Warning until 9 AM PST this morning for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

     Gale Warning until 9 PM PST this evening for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning until 3 AM PST Saturday for Pigeon Pt to Pt Pinos 0-
     10 nm.

     Small Craft Advisory until 9 AM PST this morning for Pt Pinos to
     Pt Piedras Blancas 0-10 nm.

     Gale Warning from 9 AM this morning to 3 AM PST Saturday for Pt
     Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...MM
MARINE...MM

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