Cold in California, December 2, 2022

Area Forecast Discussion
National Weather Service San Francisco Bay Area
956 PM PST Thu Dec 1 2022

.SYNOPSIS...Breezy to gusty winds and widespread rain will
impact the Bay Area and Central Coast on Thursday with drying
conditions by tonight. Mainly dry and cold on Friday before rain
returns for the upcoming weekend. Cold and dry weather returns early
next week.

&&

.DISCUSSION...as of 07:17 PM PST Thursday...The frontal passage is
now further south and completely out of our region as we start to
see some clear skies in the North Bay. Rainfall totals aligned
with our forecast where most of our area reported 0.5-1.5 inches
with the Coastal Range receiving about 1-2.2 inches of rain, which
was the highest reported rainfall for this event. Marin county
was the second highest area reporting 1-1.8 inches. The forecast
is still on track for the next weather concern, which will be the
frost/freezing temperatures for tonight into Friday morning. A
Freeze warning is in effect for North Bay, Monterey and San Benito
county, and east of Santa Clara county. With the recent rainfall
and freezing temperatures, chances for black ice is possible, so
be cautious on the roads as we head into tomorrow. The ensembles
are still showing the next rain event to occur this weekend. Still
ambiguous on timing and total rainfall expected, but we will
continue to monitor for any changes.

&&

.PREV DISCUSSION...as of 02:44 PM PST Thursday...The Bay Area and
Central Coast are currently split regarding rain this afternoon.
North of SFO is drying out, but areas to the south are very wet. A
cold front, which had a nice NCFR signature earlier today,
continues to march southward. Yesterday it looked like the front
would just blast right through the forecast area, but today it is
trending slower. As of this discussion the cold front is moving
through Monterey Bay. The intensity of the fropa may have eased on
radar a tad, but still moderate to locally heavy rain is
occurring. The front will continue to move S and E through this
afternoon and early evening. The drying trend up north will also
spread S and E through this evening. There is still a chance for a
few isolated showers behind the front early this evening, but not
widespread activity. In addition to the rain the passing front is
still producing some breezy to gusty winds with gusts 25-40 mph.
These totals will change because it's still rain, but so far
rainfall amounts are generally 0.25-1.00" with higher amounts
1.5-2" North Bay Mts, Santa Cruz Mts.

Once the precip finally ends the next weather impact will be
temperatures tonight and early Friday morning. First and
foremost, a Freeze Warning remains in effect for interior N Bay
and Southern Monterey/San Benito. Given the potentially wet/damp
conditions it will "feel" even colder. Simply put, the vulnerable
population or those without shelter will be impacted the most.
Kind of ironic that today is the first day of meteorological
winter and tonight could end up being the coldest night of the
season so far. In fact, there's a 70% chance that San Francisco DT
could actually set a record (fcst is 38 deg record is 40 deg).
Interior valleys will see more widespread 20s to lower 30s and
coast/bays will see more widespread 30s. Frost will be possible
and even some black ice given the recent rain.

Dry and cool weather is expected on Friday and early Friday
night.

After a brief break in the precip the next round of rain begins to
arrive Friday night. A moisture plume lurking off the SoCal
(remnants of current system) will move north over the Central
Coast Friday night as Saturday. Model guidance, ensembles and
deterministic, have been trending wetter for the Saturday system.
Atmospheric Guidance now puts the Santa Lucia Range in the
thresholds for a weak AR. Somewhat unusual to have a moisture AR
plume move in from the south. The real question is, how far north
does it go? Does it mainly cause heavier precip just over the
Santa Lucia Range or drift north to the Santa Cruz Mts too?
Highest confidence for Santa Lucia, but some probabilistic
guidance does show heavier rain reaching the Santa Cruz Mts. The
bigger determining factor will be an approaching upper level
trough from the north Saturday into Sunday. The timing of this
feature will help or hurt the north progression. This is all for
the heaviest rain, but everywhere in the forecast area should see
some rain Saturday. By the time the next upper level trough
arrives some more instability will be present to allow for a few
isolated thunderstorms on Sunday. Showers will linger into Monday.
Rainfall totals for the weekend: Santa Lucia 2-5" with most other
areas 0.75-1.5". WPC has much of the Central Coast in an excessive
rainfall outlook for the weekend too.

Dry and cooler weather return for next week.

&&

.AVIATION...as of 9:45 PM PST Thursday...For the 06Z TAFs.

High clouds will gradually depart from the Central Coast this
evening as a cold front exits to the south. The most likely
forecast outcome is for clear/VFR for most areas tonight with
light winds. It's worth noting that a few of the the high
resolution models develop some visibility reductions in BR
towards morning in a few areas such as the North Bay. However this
is not the consensus view and confidence isn't high enough to
include this in the TAFs. Otherwise expect VFR with light winds
during the day tomorrow. Increasing mid to high level clouds
anticipated beyond the next 24 hours as another weather system
approaches the region.

Vicinity of KSFO...VFR with light winds into Friday. FEW-SCT lower
clouds possible this evening.

KSFO Bridge Approach...Similar to KSFO.

Monterey Bay...Generally VFR with light winds. Low confidence (20
percent) in patchy stratus/BR developing near the terminals late
tonight into early Friday morning. Otherwise VFR and quiet weather
on Friday.

&&

.CLIMATE...

Daily Record Low Temperatures for December 2nd.

              12/02 Record Low          Record Year

Santa Rosa coop        25                1906
Kentfield              28                1906
Napa State Hospital    28                1932, 1928
Richmond               38                2006, 1973, 1967
Livermore coop         26                1906
San Francisco downtown 40                2009, 1906
SFO Airport            37                1967
Redwood City           30                1936
Half Moon Bay          32                2004
Oakland Museum         38                1973
San Jose               26                1906
Gilroy                 26                1990
Salinas Airport        30                2004, 1990, 1936, 1934
King City              24                1957, 1933

&&

.MARINE...as of 09:33 PM PST Thursday...The cold front is
departing to our south this evening bringing an end to any
rainfall over the southern waters. Northwest swell will continue
into early Friday bringing hazardous seas for smaller vessels. A
low pressure system over the eastern Pacific will bring another
round of rain and increasing winds to the region this weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Freeze Warning...CAZ504-506-514-516>518
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

PUBLIC FORECAST: MM/SO
AVIATION: SPM
MARINE: SPM

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