Freeze Warning 2, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1019 AM PST Thu Jan 19 2023

.SYNOPSIS...Light rain ending later this morning as a cold front
departs the area. Thereafter high pressure will bring dry weather
and cooler temperatures. Frost and freezing conditions will
return for colder inland areas into this weekend.

&&

.DISCUSSION...as of 12:40 AM PST Thursday...

Today and Tonight:

A shortwave trough now over NorCal and the Pacific Northwest will
shift east and evolve to a closed upper low over the Desert
Southwest. This will allow high amplitude ridging over the eastern
Pacific to shift into the region by this evening. A surface cold
front now bisecting the Bay Area will shift to our south later this
morning bringing an end to any lingering showers. Thereafter our
focus turns to colder air spilling into the area behind the front.
High temperatures this afternoon should only top out in the lower to
mid 50s for the lower elevations with 40s in the mountains. By
tonight, good radiational cooling should ensue with readings
dropping into the 30s nearly region-wide. The exception will be
right along the coast and bays where lows should be near 40. Frost
and freezing temperatures are expected for the North Bay Valleys,
inland East Bay, Santa Clara Valley, and inland Monterey and San
Benito Counties where a Freeze Warning is in effect. These
temperatures are a direct threat to unsheltered populations and
those without adequate access to heating. Make sure to protect
people, pets, plants, and pipes from the cold.

Friday through Thursday:

Stout upper ridging over the eastern Pacific will provide a
protective influence over our area as weather disturbances shift
inland to our east while keeping us dry. Surface high pressure will
center over the Pacific waters and subsequently strengthen through
the central Great Basin into the weekend. This pattern will promote
mostly sunny days and chilly nights. The coldest period will be on
Friday morning and from Friday night into Saturday morning. In each
case low temperatures will be mostly in the 30s with readings around
40 on the SF Peninsula. The coldest inland valleys may even dip into
the 20s. Another Freeze Warning will likely be needed in the Friday
night-Saturday morning timeframe to account for these conditions
across inland areas. Once again overnight and morning temperatures
will be hazardous to unsheltered or marginally sheltered
populations. Otherwise low temperatures will gradually moderate
after the weekend with readings mainly in the upper 30s and 40s.
Daytime highs will remain seasonally cool and mostly in the 50s to
around 60.

&&

.AVIATION...as of 10:15 AM PST Thursday...For the 18Z TAFs. VFR
conditions prevail through the day today as skies clear out in the
post-frontal environment. NNW winds of 8 to 15 knots expected
this afternoon and evening. More inland TAF sites such as KAPC and
KLVK could see winds shift NNE this evening as the upper level
trough exits California and moves eastward. Low end LLWS concerns
for KAPC as well. VFR through the TAF period with the exception of
KSTS where patchy valley fog will likely develop again into the
early morning. Lower confidence for KSNS seeing patchy fog, but
MVFR visbys included at the end of the period to account for this
possibility. Light offshore drainage winds expected tonight for
valleys.

Vicinity of SFO...VFR. NW winds will increase through the
afternoon with gusts up to 20 knots possible. Winds shift NNW
this evening and eventually NNE overnight into the early morning
Friday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay...VFR with clearing skies. NW winds will increase
this afternoon to around 8 to 12 knots. Low confidence that KSNS
will see patchy fog again this morning, but MVFR visbys included
at the end of the period. Light drainage winds tonight.

&&

.BEACHES...As of 03:28 PM Wednesday...As storms exit the
California forecast, trending into more drier conditions, the
anomalously high water levels are also diminishing down toward the
astronomical tidal predictions. However, the King Tides, which
result in the highest high tides and the lowest low tides, return
this weekend. Higher water levels will continue through early next
week resulting in minor coastal flooding in traditional low lying
areas. Those visiting the coast should be familiar with the times
and heights of local tidal levels to avoid hazards that may arise
from rapidly shifting water levels.

&&

.MARINE...as of 08:33 AM PST Thursday...Breezy northwest winds and
elevated seas persist in the post- frontal environment through
early Friday, making conditions hazardous for small craft. Long
period northwesterly swell arrives Friday evening and will
diminish through early next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Coastal Flood Advisory...CAZ006-505-506-508-509-529-530
             SCA...Mry Bay until 3 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

PUBLIC FORECAST: SPM
AVIATION: McCorkle
MARINE: McCorkle

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