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Western Storm Spreads East

A western storm will slowly spread accumulating snow into the Intermountain West and Rockies, while heavy snow persists across the southern Sierra-Nevada mountains. Locally heavy rain will be possible from parts of southeastern Arizona into western new Mexico. A strong Bering Sea storm will bring an accumulating wintry mix, coastal flooding and ice shoves to western Alaska. Read More >


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FXUS66 KMTR 040534

Area Forecast Discussion
National Weather Service San Francisco Bay Area
934 PM PST Sat Dec 3 2022

.SYNOPSIS...Steady rain over the Central Coast will diminish this
evening with another round of rain expected tonight into Sunday.
Dry and cold weather early next week with potential for lingering
rain showers.

&& of 08:53 PM PST Saturday...Widespread rain has
impacted the region through this evening with the heaviest
concentrated over the Santa Lucia Range above the Big Sur Coast
and into the Santa Cruz Mountains. 24-hour totals have exceeded 6
inches at Anderson Peak and Three Peaks while totals greater than
2 inches have been reported in the higher terrain of the Santa
Cruz Mountains. Elsewhere, totals range from 0.25" to 1.50" with
less than 0.25" across Sonoma County. This is all in response to a
weak atmospheric river that has impacted the Central Coast
through much of the day while the deeper moisture at times shifted
northward into the San Francisco Bay Area.

Precipitation continues to diminish in coverage and intensity late
this evening as the deeper moisture advection shifts inland and to
the south. Meanwhile, another cold front producing widespread
precipitation along northern Calfiornia`s coastline is approaching
the from the northwest. There will be a bit of a dry slot in between
these two systems. As such, rain will begin over the North Bay
around or after midnight before shifting southward into the San
Francisco Bay Area overnight and Central Coast early Sunday morning.
In wake of this frontal passage, isolated to scattered post frontal
showers are expected. Early in the evening, lightning was detected
well out over the Pacific near the core of the mid/upper level low.
Thus, cannot rule out an isolated thunderstorm or two early Sunday
morning. The greatest potential will be over the North Bay where the
greatest mid/upper level instability will exist.

This said, the ongoing forecast remains on track for the remainder
of the evening. Please see the discussion below for additional
details with a complete update out early Sunday morning.


.PREV of 02:28 PM PST Saturday...As expected, the Big
Sur coast has been seeing persistent rainfall through the morning
with more to come this afternoon. So far, the highest observed
total rainfall from this plume of moisture is 3.58 inches on the
very southern edge of the Big Sur Coast.

This southern plume will continue to offer steady rain chances for
Monterey Co will into the night with more scattered chances entering
the Bay Area through the evening. The highest rain rate will remain
focused on the Big Sur Coast, but again forecasted rates look to
stay below debris flow thresholds for the Monterey Co burn scars.

As the southern plume of moisture cuts off its feed and moves
inland, the next trough from the North begins to affect the North
Bay counties late tonight. Recent model updates have been slowing
the initial boundary`s strength and speed. This reduces rainfall
rates, but increases the duration of this passage, meaning rainfall
amounts only reduced slightly.

The parent low pressure of this next boundary will also move into
the area, offering scattered rain chances lasting into Tuesday
morning. Again, rates look mild, but it will be over a fair amount
of time. Rain fall totals between the time of writing and Tuesday
are mostly between 0.5" to 1" around the Bay Area. While the
southern counties of the CWA will see much less rainfall after

Temperatures are not expected to see much movement until the middle
of next week. Daily highs will stay mostly in the 40s and 50s with
lows staying in the 30s and 40s. After the mid week, expect lows to
fall into the lower 30s for most of the more interior areas, with
highs remaining cool.


.AVIATION...As of 9:30 PM Saturday... For the 6Z TAFs. Rain is
getting less intense for the moment across the region, and is
exiting from the North Bay and the Bay Area, but IFR-LIFR ceilings
continue, with visibilities still decreased, most terminals
reporting values around 2-3 miles. This break should end as a cold
front moves in. A brief period of moderate rain comes into the North
Bay at around 9-10z, and the Bay Area around 11-13z, but by the time
it reaches Monterey Bay around 14-15z it will break up into a band
of showers. The Bay Area and points south should get a break around
18-20z as showers continue impacting the North Bay, before a new
band of showers impacts the Bay Area around 4-5z. Winds will pick up
slightly as the front passes, and should increase and turn to the
southwest behind the front, but will otherwise remain light.

Vicinity of SFO... MVFR ceilings and southerly winds approaching 10
knots setting up overnight as the moisture plume moves out and the
cold front moves in around 10z. Clearing is expected by around 15z,
with southwest winds gusting to 20 knots for Sunday afternoon.
Scattered showers expected to begin around 2z, before a band of
showers develops closer to 5-6z.

SFO Bridge Approach... Similar to SFO.

Monterey Bay... MVFR ceilings at MRY, with the present IFR at SNS
clearing to MVFR overnight. Ceilings will decrease again as what
remains of the front moves through around 14z, clearing back to MVFR
or VFR as the front passes. Winds will remain light, never exceeding
10 knots in the forecast.

&& of 09:33 PM PST Saturday...Moderate to fresh
southerly winds across the waters as a stationary front sits
across the Central Coast. A cold front will pass through late
tonight through Sunday bringing increasing southwesterly winds. A
slight chance of thunderstorms north of Point Reyes exists
tonight through Sunday behind the front. A new Northwest swell
will spread through the waters tonight into Sunday creating
hazardous seas in the outer waters for smaller vessels.


.Tday...SCA...SF Bay until 9 AM
SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm from 8 AM until 3 PM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 9 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 PM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 PM



MARINE: Dial/Murdock

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