Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 271553
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
853 AM PDT Wed Mar 27 2024

...New UPDATE, MARINE...

.SYNOPSIS...
Issued at 319 AM PDT Wed Mar 27 2024

Cloud cover increases into Wednesday morning ahead of the next
rain-maker. Light rain develops in the North Bay in the mid morning
then slowly spreads across the Bay Area before a steady band of
rain arrives in the late afternoon. Showers last behind the front
into mid Thursday. Breezy to gusty winds arrive with another
round of rain at the end of the work week. Moderate rainfall and
chances for storms are expected. Drier weather returns Sunday
through early next week as high pressure builds.

&&

.UPDATE...
Issued at 852 AM PDT Wed Mar 27 2024

Light rain has started to fall across the northern portions of the
North Bay this morning as warm air advection continues. However,
widespread rain isn`t expected until later this morning/afternoon
across that region and will spread southward through the overnight
hours. Again, most of this rainfall will be light and mostly
beneficial.

&&

.SHORT TERM...
(Today and tonight)
Issued at 319 AM PDT Wed Mar 27 2024

A fairly calm night so far, but cloud cover is building as the
next system nears, brining the area back into a wet pattern.

The overnight model updates and observations have shown some slowing
of todays` cold front, which isn`t uncommon for this time of year.
The initial, warm sector showers build into the North Bay in the mid
morning with some light rain/drizzle making it into the rest of the
Bay Area into the afternoon, but the main rain band and cold front
will arrive in the late afternoon and spread across the CWA into the
evening. Winds along the front will be breezy, with some gustier
winds along the higher peaks, but not hazardously strong.

With this being a cold front followed by parent low set-up, expect
shower activity to last through Wednesday night and into Thursday as
the low pressure affects the region after the main rain band passes.

Rain rates look light to at times moderate from this first system,
causing modest rainfall totals starting this morning through
Thursday. The most interior valleys will see a few hundredths, while
most areas see a few tenths, and then the higher peaks in the North
Bay look to see over an inch.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 319 AM PDT Wed Mar 27 2024

After a brief pause in rain into Thursday evening, another
quicker-moving cold front and low pressure move into the upper
level trough pattern. The momentum of this next system will pull
the trough farther south and placing the trough axis into the Bay
Area. What does this mean? Increased moisture arriving into the
Bay Area and Central Coast compared to today`s system, and a cool-
looking momentum transfer on the forecast maps.

The overnight forecast update took some time looking at this second
system, and there still is a fair amount of variability possible.
The current trend pushes the focus of this system`s main rain band
farther south, increasing rain amounts along Big Sur, and reducing
them for the North Bay. Thunderstorm and shower chances behind the
rain band still look fairly evenly spread across the Bay Area and
Central Coast Friday night through Saturday evening, peaking around
25% during that time frame.

Rainfall totals from Thursday night through early Sunday morning
look to range from:

-0.5" to 1" for most areas
-1" to 1.25" for coastal low lands and interior North Bay
-1.25" to 2" for higher elevations along the coast
- and above 2" for the highest peaks along the coast with some
isolated areas on the Big Sur Coast reaching above 3"

Winds will be stronger with this next system, but the variability
makes it difficult to pin down which spots will be most affected,
but breezy to gusty conditions should be expected Friday afternoon
and into that night.

This will be something worth checking back in on within the next few
forecast updates.

Beyond these back-to-back systems, dry weather returns as an upper
level ridge snaps into place over the California Coast into the next
work week. This will push any oncoming rain systems North and into
the Washington and Oregon coasts.

&&

.AVIATION...
(12Z TAFS)
Issued at 441 AM PDT Wed Mar 27 2024

A low pressure system and its associated warm sector will begin
bringing rain to the terminals by mid-morning. The cold front from
this low pressure system will begin moving across the region
tomorrow afternoon from northwest to southeast, bringing more
organized, steady rain and breezy to gusty S/SW winds to the
terminals through its passage. Winds return to westerly flow behind
the cold front. Rain chances diminish towards the end of the TAF
period.

Vicinity of SFO...Currently MVFR with breezy southerly flow.
Southerly winds will be on the increase into the afternoon ahead and
through the cold frontal passage. Initial rain in the afternoon will
be light via the warm sector with an organized, more steady round of
rain set to move through in the evening as the cold front passes.
Winds return to westerly flow behind the cold front. Chances for
rain taper off towards the end of the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with southerly flow at MRY
and VFR and calm at SNS. Ahead and through the cold frontal passage,
rain and winds that will become breezy to gusty out of the W/SW will
impact the terminal.

&&

.MARINE...
(Today through Monday)
Issued at 852 AM PDT Wed Mar 27 2024

Moderate winds gradually turning S to SW through Wednesday as a
weak cold front, producing scattered light to moderate showers,
moves through the coastal zones. A second, stronger low pressure
system will reach the coastal waters Friday, bringing moderate
precipitation, gusty southerly winds, and allow for wave heights
to build. This second system will create widespread conditions
that are hazardous to small crafts. Long period northwesterly
swell will continue to abate through the waters through the end of
the month.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Pt Arena to Pt Reyes 0-10 nm-SF Bay N of Bay
     Bridge.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT
     Thursday for Mry Bay.

     Small Craft Advisory from 3 AM Thursday to 3 AM PDT Friday for
     Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 3 PM Thursday to 3 AM PDT Friday for
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
     Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory until 9 PM PDT this evening for Pt Arena to
     Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 AM Thursday to 3 AM PDT Friday for
     Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

UPDATE...RGass
SHORT TERM...Murdock
LONG TERM....Murdock
AVIATION...Sarment
MARINE...Kennedy

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