National Weather Service - Area Forecast Discussion

FXUS66 KMTR 050523

Area Forecast Discussion
National Weather Service San Francisco Bay Area
923 PM PST Sun Dec 4 2022

.SYNOPSIS...Intermittent rain showers and potential for isolated
thunderstorms will persist through Monday. Dry and colder weather
returns by midweek followed by another chance of rain late in the

&& of 09:00 PM PST Sunday...The core of a mid/upper
level low can be seen on satellite imagery this evening off of
the northern California coast. This feature produced isolated to
at times scattered rain showers over the San Francisco Bay Area
this evening. Earlier in the day, more widespread showers and even
a few thunderstorms impacted the North Bay. Rainfall amounts
range from a few hundredths of an inch to around 0.10" where
showers have moved overhead with isolated amounts greater than
0.25 within heavier downpours.

The core of the aforementioned system will nudge closer to the
northern California coast overnight and allow for additional rain
showers and even isolated thunderstorms to rotate through the
region. By early morning, rain showers will also shift southward and
impact more of the San Francisco Bay Area and Central Coast. Again,
rainfall amounts will be spotty and depend on the exact track of
more organized bands of rain showers. There remains enough instability
aloft to produce isolated thunderstorms which have been detected at
times throughout the evening offshore and near the northern
California coast. All this said, the ongoing forecast for tonight
remains on track with no updates anticipated at this time. For more,
please see the forecast discussion below.


.PREV of 01:27 PM PST Sunday...Shower and storm activity
continue in the North Bay as the boundary stalls. So far, the
day`s rainfall has added up well in the North Bay. Some of the
coastal mountains have reached around 0.75" but the scattering of
the bands of rain have prevented more uniform rainfall totals,
meaning areas like the Sonoma Co airport seeing less than a
quarter of an inch while the east side of Santa Rosa seeing around
half an inch.

Lightning activity overall has reduced since the mid morning, but a
few strokes have been detected in the North Bay to start the
afternoon. A few more cells will form this afternoon, but it does
look the the overall energy from this batch of rain is reducing.

More rain follows into the late night as the parent low for this
system makes its way south and into the Bay Area. Expect increased,
and more organized rain chances to begin in the late night as the
next band of rain moves in from the northwest. This will expand
southeast through much of Monday and will be followed by scattered
showers that will last well into Tuesday. Rainfall rates from this
next rain band and scattered showers look to be mild overall, but
there still may be a few cells that could turn to storms and offer
more moderate rainfall. The current forecast adds another 0.25" to
0.50" to the rainfall totals across much of the area through Tuesday
afternoon, more interior portions of Monterey and San Benito
counties, however, will have much more modest rain totals.

A cold morning followed by a dry day is expect for Wednesday, but
rain chances look to return Thursday and carry into the weekend.
This will be a similar setup, where an initial boundary moves
through and will be quickly followed by the parent low. This will
result in another steady going rain event for next weekend.


.AVIATION...As of 9:20 PM Sunday... For the 6Z TAFs. VFR
prevails throughout the region. Some scattered showers across the
area tonight, mostly offshore heading into the North Bay. Updates in
model data have alowed further refinement in the impact of the band
of showers tonight, with the band expected in the North Bay 10-11z,
the SF Bay Area 14-15z, and the Monterey Bay region 15-16z. Expect
several hours of moderate rainfall, MVFR ceilings, and isolated
thunderstorms while under the band. The showers should clear out by
18z, with scattered showers throughout the rest of the TAF period.
Winds remain light and mainly from the south tonight. For Monday
morning, expect winds to pick up and veer to a more southwesterly

Vicinity of SFO... Generally VFR, with MVFR ceilings as the bands of
showers move through around 14-17z. Then scattered showers for the
rest of the TAF period. Winds remain light tonight, then pick up
with the frontal passage and turn towards the west-southwest on
Monday. Models still suggesting a new patch of rainfall towds the
end of the TAF period, although confidence in timing is low.

SFO Bridge Approach... Similar to SFO.

Monterey Bay... VFR continues for the next few hours with light
winds. Band of showers expected to impact between 13-18z, with a
slight increase in winds and a decrease to MVFR ceilings associated
with the band. Scattered showers expected for the rest of Monday.
Winds pick up on Monday morning. MRY turns to the west early with
SNS remaining more southeasterly until the afternoon, when it too
turns to the west.

&& of 09:23 PM PST Sunday...Moderate southwest winds
increasing slightly tonight with some  locally stronger gusts
along a weak frontal boundary. Scattered  showers and some
isolated thunderstorms in the northern waters are possible through
Monday. Winds veer to the west and then the  northwest Monday, as
low pressure approaches the coast. Northwest  swell will diminish
tonight and lighter winds arrive by midweek.


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 PM



MARINE: Lorber/Dial

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NWS MTR Office Area Forecast Discussion