767
FXUS66 KMTR 120038
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
438 PM PST Wed Dec 11 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 300 PM PST Wed Dec 11 2024

Key Messages:
- Multiple rounds of rainfall tonight through the weekend
- Light rain may start as soon as 7-8pm tonight across the North Bay
- Periods of moderate rain after midnight through sunrise tomorrow
over the North Bay
- Rainfall shifts south and east across the Bay Area, East Bay and
rest of the Central Coast through the remainder of tomorrow morning
- First wave of rainfall exits east by early Thursday afternoon
- More impactful, longer duration rainfall expected Friday evening
through Saturday with gusty south winds during that time as well
- Another round of primarily light rain arrives late Sunday into
Monday with minor impacts expected
- Coastal flooding impacts will be further enhanced by the timing of
a King Tide tomorrow through the weekend, which will also result in
beach hazard concerns

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 300 PM PST Wed Dec 11 2024

Not much change in thinking wrt rainfall set to arrive across the
North Bay later this evening. The North Bay coastal ranges will
begin to see pre-frontal rain develop as early as 7-8pm tonight as a
strengthening closed low approaches NorCal later during the
overnight. Steadier, light to moderate rainfall will gradually
expand in coverage after midnight from the North Bay south and east
across the Bay Area and the remainder of the Central Coast,
eventually shifting east of our area by early tomorrow afternoon.

Overall, portions of the North Bay, especially the coastal ranges
can expect 1.5 to 2.5" of rainfall by late tomorrow morning. The
highest rainfall rates should peak at around 0.5"/hr in the 1am-4am
time frame along the coastal ranges, and otherwise hover around
0.25"/hr as the system moves inland Thursday morning.

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 300 PM PST Wed Dec 11 2024

Light rain will linger Thursday afternoon through early Friday as
weak mid-level shortwaves transect our area out ahead of the next
system as it strengths over open water. The leading edge of more
intense rainfall rates arrive along the coastal ranges of the North
Bay by Friday evening. A +100kt H30 SSW-NNE oriented jet develops
over our area Friday night with more widespread moderate rainfall
expected during the overnight Friday, beginning over the North
Bay once again, gradually spreading south and east through the
remainder of the day Saturday across the rest of our area. Coastal
ranges farther south from the Bay Area to the Santa Lucias may
see 1-2" Friday night through early Sunday with the remainder of
our interior locations looking at wetting rains between 0.25" to
0.75". Sunday is mostly dry before another disturbance arrives for
the beginning of next week. Attm, it appears to be a fairly
progressive trough, with 0.5" to 1.0" possible from the Bay Area
north, with lesser amounts across the East Bay and the remainder
of the Central Coast.

&&

.AVIATION...
(00Z TAFS)
Issued at 438 PM PST Wed Dec 11 2024

A cold front is located 400 miles northwest of San Francisco and
is moving quickly southeastward at approx 40 mph. As advertised
the front will bring rain to the Bay Area and north Central Coast
tonight and Thursday morning. Dry air precedes the front therefore
some initial loss of precipitation is likely along with evaporational
cooling taking place well before the predawn arrival of the cold
frontal rain. Air mass stability prevailing tonight will minimize
surface winds, while winds aloft may become locally breezy to gusty,
and at this time not expecting low level wind shear tonight and
Thursday morning at the terminals. Post cold frontal winds becoming
gusty Thursday, with a few passing showers lingering during the
day.

Vicinity of SFO...VFR prevailing through mid evening, ceiling and
visibility are forecast to lower to MVFR overnight with rain
developing. Cold frontal passage is forecast 11z Thursday with
west wind gusty to 25 to near 30 knots. A few lingering showers
and breezy to gusty Thursday otherwise VFR.

SFO Bridge Approach...Slant range visibilities reduced due to
haze. Gusty wind developing early Thursday morning with the cold
front will quite likely mix out the haze.

Monterey Bay Terminals...Low to moderate confidence VFR prevails
through the evening; HREF output has recently showed low clouds
/IFR/ nearing the coastline well before the cold front early
Thursday morning. 00z TAFs continue with gradually increasing low
clouds /MVFR/ and rain developing late tonight and Thursday morning,
cold frontal passage forecast 12z-13z Thursday with westerly breezes
increasing a little more later Thursday morning.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 412 PM PST Wed Dec 11 2024

A low pressure system will bring rain and gusty winds tonight and
Thursday. Wet weather continues late this week and early weekend
with another low pressure system from the Pacific. Dry weather
returns for Sunday then another low brings rain to the coastal
waters and bays Monday. Wave heights will remain rough to very
rough mid to late week.

&&

.BEACHES...
Issued at 201 PM PST Wed Dec 11 2024

There will be multiple hazards across the Bays, Pacific Ocean, and
their associated beaches as three storm systems take aim at the West
Coast and King Tides return. A Coastal Flood Advisory has been
issued from 6 AM Thursday through 1 PM Monday along the bayshore of
the San Francisco Bay and San Pablo Bay with the highest tides: 6.74
ft at 8:12 am Thursday, 6.98 ft at 8:54 am Friday, 7.07 ft at 9:37
am Saturday, 7.02 ft at 10:22 am Sunday, and 6.82 ft at 11:08 am
Monday. These very high tides in tandem with long period
northwesterly swell will allow for large sets of waves to run a lot
farther up the beaches. A High Surf Advisory has been issued for 1
PM Thursday through 4 AM Friday for all west and northwest facing
beaches for breaking waves of 18-22 feet. Other impacts will be rip
current risk, longshore current risk, gale-force gusts, slight
thunderstorm chances, and widespread rainfall. There are going to be
poor conditions everywhere, especially on the water or at the
beach.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 6 AM Thursday to 1 PM PST Monday for
     CAZ006-506-508.

     High Surf Advisory from 1 PM Thursday to 4 AM PST Friday for
     CAZ006-505-509-530.

PZ...Small Craft Advisory from 9 PM this evening to 3 PM PST Thursday
     for SF Bay N of Bay Bridge.

     Small Craft Advisory from 3 AM Thursday to 3 AM PST Friday for
     Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos
     10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

     Small Craft Advisory until 3 AM PST Friday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Canepa
MARINE...Sarment

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